Comprehensive Organic Functional Group Transformations, Volume4 (Synthesis: Carbon with Two Heteroatoms, Each Attached by a Single Bond)

1217 Pages·2003·12.12 MB·English

by  Alan R. Katritzky, Otto Meth-Cohn, and Charles W. Rees (Editors-in-Chief)

Comprehensive Organic Functional
Group Transformations, Volume 4
Elsevier, 2003

Editors-in-Chief: Alan R. Katritzky, Otho Meth-Cohn, and Charles W. Rees

Synthesis: Carbon with Two Heteroatoms, Each Attached by a
Single Bond

Part I: Tetracoordinated Carbon Functions Bearing Two Heteroatoms, R2CXX′

4.01 Dihalo Alkanes, R2C(Hal)2, Pages 1-40, Robert A. Hill

4.02 Functions Incorporating a Halogen and a Chalcogen, Pages 41-93,
Niall W. A. Geraghty
4.03 Functions Incorporating a Halogen and Another Heteroatom Group Othe
Than a Chalcogen, Pages 95-157, Alex C. Campbell and David R. Jaap
1 2
4.04 Functions Bearing Two Oxygens, R 2C(OR )2, Pages 159-214, David
T. Macpherson and Harshad K. Rami
4.05 Functions Incorporating Oxygen and Another Chalcogen, Pages 215-241,
Richard H. Wightman
4.06 Functions Incorporating Two Chalcogens Other Than Oxygen, Pages 243-291,
Yannick Vallée and Andrew Bulpin
4.07 Functions Incorporating a Chalcogen and a Group 15 Element, Pages 293-349,
Christopher D. Gabbutt and John D. Hepworth
4.08 Functions Incorporating a Chalcogen and a Silicon, Germanium, Boron or
Metal, Pages 351-402, Max J. Gough and John Steele
4.09 Functions Bearing Two Nitrogens, Pages 403-449, Derek R. Buckle and Ivan
L. Pinto
4.10 Functions Containing a Nitrogen and Another Group 15 Element, Pages
451-504, Frances Heaney by kmno4
4.11 Functions Incorporating a Nitrogen and a Silicon, Germanium, Boron or Metal,
Pages 505-541, John Steele and Max J. Gough
4.12 Functions Containing One Phosphorus and Either Another Phosphorus or As,
Sb, Bi, Si, Ge, B or a Metal, Pages 543-589, R. Alan Aitken
4.13 Functions Containing at Least One As, Sb or Bi with or without a Metalloid
(Si or Ge) or a Metal, Pages 591-600, William M. Horspool
4.14 Functions Containing at Least One Metalloid (Si, Ge or B) Together with
Another Metalloid or Metal, Pages 601-665, Christopher G. Barber
4.15 Functions Containing Two Atoms of the Same Metallic Element, Pages
667-703, William J. Kerr and Peter L. Pauson
4.16 Functions Containing Two Atoms of Different Metallic Elements, Pages
705-727, William J. Kerr and Peter L. Pauson

Part II: Tricoordinated Carbon Functions Bearing Two Heteroatoms, R2C=CXX′

4.17 Functions Incorporating Two Halogens or a Halogen and a Chalcogen, Pages
729-788, Peter D. Kennewell, Robert Westwood and Nicholas J. Westwood
4.18 Functions Incorporating a Halogen or Another Group other than a Halogen
or a Chalcogen, Pages 789-822, David I. Smith
4.19 Functions Bearing Two Chalcogens, Pages 823-877, Gary N. Sheldrake

4.20 Functions Containing a Chalcogen and Any Group Other Than a Halogen or
a Chalcogen, Pages 879-965, Peter D. Kennewell, Robert Westwood and
Nicholas J. Westwood
4.21 Functions Containing at Least One Nitrogen and No Halogen or Chalcogen,
Pages 967-1020, Graham L. Patrick
4.22 Functions Containing at Least One Phosphorus, Arsenic, Antimony
or Bismuth and No Halogen, Chalcogen or Nitrogen, Pages 1021-1042,
John M. Berge
4.23 Functions Containing at Least One Metalloid (Si, Ge or B) and No Halogen,
Chalcogen or Group 15 Element; also Functions Containing Two Metals,
Pages 1043-1070, Richard A. B. Webster

Part III: Tri- and Dicoordinated Ions, Radicals and Carbenes Bearing Two Heteroatoms
+ 1 2 − 1 2 · 1 2 1 2
(RC X X , RC X X , RC X X , :CX X )

4.24 Tri- and Dicoordinated Ions, Radicals and Carbenes Bearing Two Heteroatoms
+ 1 2 − 1 2 1 2 1 2
(RC X X , RC X X , RC · X X , :CX X ), Pages 1071-1083, William M. Horspool
4.25 References to Volume 4, Pages 1085-1229

by kmno4
4.01
Dihalo Alkanes, R2C(Hal)2
ROBERT A. HILL
University of Glasgow, UK
3[90[0 GENERAL METHODS 1
3[90[1 DIFLUORO ALKANES*R1CF1 1
3[90[1[0 Di~uoro Alkanes from Alkanes 1
3[90[1[1 Di~uoro Alkanes from Dihalo Alkanes 2
3[90[1[2 Di~uoro Alkanes from Trihalo Alkanes 4
3[90[1[3 Di~uoro Alkanes from Alkenes 4
3[90[1[4 Di~uoro Alkanes from Alkynes 5
3[90[1[5 Di~uoro Alkanes from Di~uorocarbene 6
3[90[1[6 Di~uoro Alkanes from Aldehydes and Ketones 7
3[90[1[7 Di~uoro Alkanes from Imines 09
3[90[2 DICHLORO ALKANES*R1CCl1 00
3[90[2[0 Dichloro Alkanes from Alkanes 00
3[90[2[1 Dichloro Alkanes from Dihalo Alkanes 02
3[90[2[2 Dichloro Alkanes from Trihalo Alkanes 02
3[90[2[3 Dichloro Alkanes from Alkenes 03
3[90[2[4 Dichloro Alkanes from Alkynes 04
3[90[2[5 Dichloro Alkanes from Dichlorocarbene 05
3[90[2[6 Dichloro Alkanes from Aldehydes and Ketones 07
3[90[2[7 Dichloro Alkanes from Imines 08
3[90[3 DIBROMO ALKANES*R1CBr1 08
3[90[3[0 Dibromo Alkanes from Alkanes 08
3[90[3[1 Dibromo Alkanes from Dihalo Alkanes 11
3[90[3[2 Dibromo Alkanes from Trihalo Alkanes 12
3[90[3[3 Dibromo Alkanes from Alkenes 12
3[90[3[4 Dibromo Alkanes from Alkynes 13
3[90[3[5 Dibromo Alkanes from Dibromocarbene 13
3[90[3[6 Dibromo Alkanes from Aldehydes and Ketones 14
3[90[3[7 Dibromo Alkanes from Imines 16
3[90[3[8 Dibromo Alkanes from Carboxylic Acids 16
3[90[4 DIIODO ALKANES*R1CI1 17
3[90[4[0 Diiodo Alkanes from Alkanes 17
3[90[4[1 Diiodo Alkanes from Halo Alkanes 17
3[90[4[2 Diiodo Alkanes from Alkynes 18
3[90[4[3 Diiodo Alkanes from Diiodocarbene 18
3[90[4[4 Diiodo Alkanes from Imines 18
3[90[5 FLUOROHALO ALKANES*R1CFHal 29
3[90[5[0 Chloro~uoro Alkanes*R1CClF 29
3[90[5[0[0 Chloro~uoro alkanes from halo alkanes 29
3[90[5[0[1 Chloro~uoro alkanes from halo alkenes 29
3[90[5[0[2 Chloro~uoro alkanes from chloro~uorocarbene 21
3[90[5[0[3 Chloro~uoro alkanes from imines 21
3[90[5[0[4 Chloro~uoro alkanes from carboxylic acids 22
3[90[5[1 Bromo~uoro Alkanes*R1CBrF 22
3[90[5[1[0 Bromo~uoro alkanes from halo alkanes 22
3[90[5[1[1 Bromo~uoro alkanes from halo alkenes 23
0
1 Dihalo Alkanes
3[90[5[1[2 Bromo~uoro alkanes from bromo~uorocarbene 24
3[90[5[1[3 Bromo~uoro alkanes from carboxylic acids 24
3[90[5[2 Fluoroiodo Alkanes*R1CFI 25
3[90[5[2[0 Fluoroiodo alkanes from halo alkanes 25
3[90[5[2[1 Fluoroiodo alkanes from halo alkenes 25
3[90[5[2[2 Fluoroiodo alkanes from ~uoroiodocarbene 25
3[90[5[2[3 Fluoroiodo alkanes from carboxylic acids 26
3[90[6 CHLOROHALO ALKANES*R1CCl Hal"not F# 26
3[90[6[0 Bromochloro Alkanes*R1CBrCl 26
3[90[6[0[0 Bromochloro alkanes from halo alkanes 26
3[90[6[0[1 Bromochloro alkanes from halo alkenes 27
3[90[6[0[2 Bromochloro alkanes from bromochlorocarbene 27
3[90[6[0[3 Bromochloro alkanes from ketones 27
3[90[6[0[4 Bromochloro alkanes from carboxylic acids 27
3[90[6[1 Chloroiodo alkanes*R1CClI 28
3[90[6[1[0 Chloroiodo alkanes from halo alkanes 28
3[90[6[1[1 Chloroiodo alkanes from halo alkenes 28
3[90[6[1[2 Chloroiodo alkanes from ketones 39
3[90[6[1[3 Chloroiodo alkanes from carboxylic acids 39
3[90[7 BROMOIODO ALKANES*R1CBrI 39
3[90[0 GENERAL METHODS
There are many general methods for the preparation of ‘em!di~uoro\ ‘em!dichloro and ‘em!
dibromo alkanes[ These are given in detail in the following sections[ Direct halogenation of alkanes
is of limited use as there is generally little control of the site of halogenation[ The method can be
useful\ however\ when there is some control such as halogenation of benzylic positions or a to a
carbonyl group[ Replacement of one halogen for another can be useful for diiodo and mixed ‘em!
dihalo alkanes\ but it is often very di.cult to control the degree of exchange[ One of the major
problems in the generation of ‘em!dihalo alkanes by this method is the possibility of elimination of
hydrogen halide under the reaction conditions[ This is a particular problem for dihalo alkanes where
one of the halides is bromine or iodine[
Addition of hydrogen halides or halogens to halo alkenes has been used extensively for the
production of dihalo alkanes[ Radical addition of hydrogen halides often leads to 0\1!dihalo
compounds and care must be taken to reduce the possibility of radical formation[ Other problems
of direction of addition occur when interhalogen compounds are added across halo alkenes^ mixtures
of products are often obtained[
Dihalocarbenes have been used extensively in addition reactions to double bonds to form
dihalocyclopropane derivatives[ There are many methods for the generation of carbenes or e}ecting a
carbene transfer\ particularly for di~uoro!\ dichloro! and dibromocarbene[ The other dihalocarbenes
have been studied less extensively[
The conversion of an aldehyde or ketone into a dihalo alkane works well with ~uoro and chloro
alkanes\ but bromo and iodo alkanes are easily hydrolysed back to the aldehyde and ketone[ Many
preparations of dibromo and diiodo alkanes result in carbonyl compounds as side products[
3[90[1 DIFLUORO ALKANES*R1CF1
The preparation of ‘em!di~uoro alkanes is included in a general review by Henne on the synthesis
of aliphatic ~uorine compounds �33OR"1#38�[
3[90[1[0 Di~uoro Alkanes from Alkanes
Direct ~uorination of saturated compounds has been used since 0899 to replace hydrogen by
~uorine �33OR"1#38�[ However\ the reaction is not easy to control^ most organic compounds react
violently with ~uorine[ The reaction of elemental carbon with ~uorine has been reported to give a
mixture of products from which per~uoropropane\ per~uorobutane and per~uoropentane have
been isolated �26JA0396�[ This method is clearly not of general application[ More!controlled ~uo!
rination of ethane using ~uorine diluted with nitrogen yielded partially ~uorinated ethanes from
Di~uoro Alkanes 2
which CHF1CHF1 and CHF1CH1F could be isolated �39JA0060�[ Electrochemical ~uorination of
ethane with a solution in hydrogen ~uoride is a more controllable method but again mixtures were
obtained\ however\ CH2CHF1 could be obtained in usable amounts �55BCJ108�[ Cobalt tri~uoride
is a useful reagent for the per~uorination of unsaturated compounds[ For example\ cyclopentane
can be per~uorinated "Equation "0##\ however the substitution of the last few hydrogens in a
compound requires higher temperatures �40JA3130�[ Per~uorocyclohexane has been prepared from
benzene with ~uorine and a catalyst "Equation "1## �49JCS1578�[ Gold was found to be the best
catalyst[ Per~uorocyclohexane has also been made from methyl benzoate by the action of potassium
tetra~uorocobaltate at high temperatures "Equation "2## �62JFC"2#218�[ Active methylene compounds
have been reported to be ~uorinated e.ciently with two equivalents of sodium ethoxide in ethanol
followed by perchloryl ~uoride "Equations "3#�"5## �47JA5422�^ however\ a later report suggests that
the reaction is quite complex �55JOC805�[
F F
F F
CoF3, 325 °C
(1)
F F
F F
F F
F F
F F
F2, Au F F
(2)
40% F F
F F
F F
F F
F F
CO2Me
KCoF4, 300 °C F F
(3)
25% F F
F F
F F
O
O EtONa, EtOH, FClO
3
CO2Et (4)
CO2Et
59%
F F
CO2Et
F CO2Et
EtONa, EtOH, FClO3
(5)
CO2Et 84% F CO2Et
O O
O O EtONa, EtOH, FClO
3
(6)
77%
F F
3[90[1[1 Di~uoro Alkanes from Dihalo Alkanes
The substitution of halide in dihalo alkanes using metal ~uorides is of general use for the
preparation of di~uoro alkanes as the corresponding dichloro and dibromo alkanes are generally
more accessible[ The ease of substitution is I�Br�Cl^ the substitution of chlorine frequently
requires very high temperatures[ Potassium ~uoride will displace the chlorine in the relatively
reactive a!keto alkyl chlorides "for example Equation "6## �75JA6628�\ whereas the chlorine of N\N!
diethylchloro~uoroacetamide can only be displaced at high temperatures "Equation "7##
�66CCC1426�[ Substitution of unreactive chlorines such as in dichloromethane requires harsher
conditions\ for example a melt of potassium hydrogen di~uoride\ KHF1 "Equation "8## �55AG"E#203�[
KHF1 has also been used to prepare 0\0!di~uoroacetone from 0\0!dichloroacetone "Equation "09##
�60JCS"C#168�[ Mercuric ~uoride has been extensively used for the preparation of ~uoro alkanes by
displacement �33OR"1#38�[ Bromine is substituted at low temperature with good yields "Equation
"00## whereas chlorine requires high temperatures and results in low yields "Equation "01## �25JA778�[
3 Dihalo Alkanes
O O
KF
Cl F
(7)
Ph Ph
28%
Cl F
O O
KF, 140 °C
Cl F
(8)
NEt2 NEt2
75%
F F
KHF2
Cl Cl F F
(9)
82%
O O
KHF2
Cl F
(10)
50%
Cl F
Br F
HgF2, 0 °C
(11)
Br F
Cl F
HgF2, 140 °C
(12)
Cl Cl
Cl 10% F
Dibromo alkanes are generally smoothly substituted by mercuric ~uoride "Equation "02## but
2\2!dibromobutan!1!one gives side reactions including the production of diacetyl "Equation "03##
�66JOC2416�[ Silver ~uoride has been used in these reactions^ however\ it is di.cult to prepare in
anhydrous form and it forms insoluble\ complex silver halides �33OR"1#38�[ Antimony tri~uoride
with a catalytic amount of bromine converts dichloro"diphenyl#methane into di~uoro!
"diphenyl#methane in high yield "Equation "04## �27JA753�[ Antimony penta~uoride is very e}ective
at substituting alkyl bromides "Equation "05## and alkyl chlorides "Equation "06## but it does not
exchange vinyl halides �55JA1370�[ A mixture of antimony tri~uoride\ antimony pentachloride and
hydrogen chloride has been used to convert 1\1!dichlorobutane into 1\1!di~uorobutane "Equation
"07## but many side reactions occurred �68JFC"02#214�
O O
HgF2
(13)
Ph Ph
89%
Br Br F F
O
O
HgF2
(14)
Br Br O
Cl Cl SbF
3, Br2 (cat.), 140 °C F F
(15)
Ph Ph Ph Ph
Br Br F F
SbF5, 109 °C
(16)
51%
Br Br Br Br
Cl Cl F F
SbF5, 110 °C
(17)
Cl Cl Cl Cl
Cl Cl SbF3, SbCl5, HCl F F
(18)
Di~uoro Alkanes 4
3[90[1[2 Di~uoro Alkanes from Trihalo Alkanes
Reduction of the bromodi~uoromethyl group with sodium borohydride in DMSO seems an
attractive method of preparation of compounds containing the di~uoromethyl group as long as the
starting material is readily available as "Equation "08## �80JOC3211�[
F F
F
NaBH4, DMSO
Br F (19)
51%
Br
3[90[1[3 Di~uoro Alkanes from Alkenes
Addition of an acid to a 0\0!di~uoro alkene will lead to a di~uoromethyl group[ The high
electronegativity of ~uorine ensures that hydrogen adds to the carbon bearing the ~uorines[ Thus
hydrogen bromide "Equation "19## and hydrogen iodide "Equation "10## add e.ciently to 0\0!
di~uoroethene �45JCS50�[ Methanol will add across tetra~uoroethene in the presence of a catalytic
amount of sodium methoxide "Equation "11## �40JA0218�[ The addition to the electron!de_cient
tetra~uoroethene is initially by nucleophilic attack[ Cyanide will add to chlorotri~uoroethene to
give\ after acid hydrolysis\ 2!chloro!1\1\2!tri~uoropropanoic acid "Equation "12## �59OSC"4#128�[
Tetra~uoroethene can be alkylated using aluminum trichloride as a catalyst\ for example\ dichloro!
~uoromethane can be e}ectively added across the double bond as "Equation "13## �60CCC0756�[
F F
HBr
Br
(20)
F 100% F
F F
HI
I
(21)
F 100% F
F F
MeOH, MeONa (cat.), 35 °C, 5 h F
F F
(22)
F OMe
81%
F F
F i, KCN F
+ F
ii, H
Cl Cl
(23)
F CO2H
76–79%
F F
F
F
CHFCl2, AlCl3, 10 °C, 5 h
F F
(24)
F Cl
58% F
3C
F
Cl
The �1�1� adducts of ~uoro alkenes can be prepared at high temperatures\ probably involving a
radical mechanism[ Tetra~uoroethene can be dimerised at 599>C to give per~uorobutane "Equation
"14##^ temperatures above 599>C give various side reactions including polymerisation �42JCS1972�[
Mixed cycloaddition reactions such as tetra~uoroethene with ethene as in "Equation "15##\ with
butadiene "Equation "16## and with acrylonitrile "Equation "17## are possible\ as they occur much
more readily than the dimerisation of tetra~uoroethene �38JA389�[ Tetra~uoroethene will also add
to acetylene to give 2\2\3\3!tetra~uorocyclobutene "Equation "18## �50JA271�[ A variety of other
~uorinated ethenes will cyclodimerise "Equations "29# and "20## at lower temperatures than tetra!
~uoroethene �36JA168�[ Intramolecular �1�1� cycloaddition of 0\0!di~uorobutadiene takes place
under UV irradiation "Equation "21## �76JOC0761�[
5 Dihalo Alkanes
F F
F
600 °C F F
F
(25)
F
F F
42%
F
F F
F
F
150 °C, 8 h F
F
F + H2C CH2 (26)
F
40%
F
F
F
F
125 °C, 8 h F
F
+ (27)
F
F
90%
F
F
F
F
150 °C, 8 h F
F
+ (28)
F CN
F
84%
F CN
F
F
F
225 °C, 12 h F
F
+ H H (29)
F
F
35%
F
F
F F
F
200 °C, 12 h F F
Cl
(30)
F
Cl Cl
80%
Cl
Cl Cl
F F
F
200 °C, 8 h F F
Cl
(31)
F
Cl Cl
80%
F
F F
F F
hν, 4 days
F (32)
F
3[90[1[4 Di~uoro Alkanes from Alkynes
The addition of two equivalents of hydrogen ~uoride across a triple bond is a general method of
preparing di~uoro alkanes "Equation "22## �36JA170�[ Fluorination of alkynes by ~uorine in meth!
anol leads to the formation of a ‘em!di~uoro dimethyl acetal "Equation "23## �75JA6628�[
HF F
F
Cl (33)
Cl
50%
OMe
MeO
F2, MeOH
F
Ph (34)
Ph
F
Di~uoro Alkanes 6
3[90[1[5 Di~uoro Alkanes from Di~uorocarbene
The generation of di~uorocarbene has been extensively reviewed �52OR"02#44\ B!58MI 390!90\ B!60MI
390!90\ 66FCR008\ B!74MI 390!90�[ Di~uorocarbene transfer is most commonly achieved by decompo!
sition of a tri~uoromethyl�metal complex[ Pyrolysis of trimethyltri~uoromethyl tin generates
per~uorocyclopropane "Equation "24##\ formed by di~uorocarbene dimerisation to tetra!
~uoroethene\ which undergoes a di~uorocarbene addition �59JA0777�[ Pyrolysis of potassium
tri~uoromethyl~uoroborate also gives per~uorocyclopropane together with per~uorocyclobutane
"Equation "25## �59JA4187�[ The complex of bis"tri~uoromethyl#cadmium and DIGLYME reacts
with acetyl chloride to produce acetyl ~uoride and di~uorocarbene\ which can be trapped with
1\2!dimethylbut!1!ene in high yield "Equation "26## �70JA1884�[ Metallic lead and dibromo!
di~uoromethane have been used to produce di~uorocarbene and its capture by several alkenes
studied �70ZN"B#0264�[ Tetrabutylammonium bromide was added to form a complex with the PbBr1
produced in the reaction[ Excellent yields were achieved with 1\2!dimethylbut!1!ene "Equation "27##
but the yields decrease with less substituted alkenes "Equations "28# and "39##[
F F
150 °C, 20 h
Me3SnCF3 F F (35)
F F
F F
F F
300 °C F F
KCF3BF3 F F + (36)
F F
F F
F F
F F
(CF3)2Cd, DIGLYME, AcCl, –27 °C
(37)
70%
F F
CBr2F2, Pb, Bu4NBr
(38)
80–90%
F F
Ph
CBr2F2, Pb, Bu4NBr
Ph (39)
55%
F F
Ph CBr2F2, Pb, Bu4NBr
(40)
17%
Ph
Bromodi~uoromethylphosphonium salts\ prepared in situ\ are good sources of di~uorocarbene[
Treatment with caesium ~uoride formed di~uorocarbene\ which added to 1\2!dimethylbut!1!ene
"Equation "30## �62JA7356�\ whereas potassium ~uoride was used likewise with butadiene "Equation
"31## �71JA1383�[ Di~uorotris"tri~uoromethyl#phosphorane has been used to transfer di~uoro!
carbene to a variety of halogenated alkenes "Equation "32## �69JCS"C#067�[
F F
CBr2F2, PPh3, CsF, RT, 24 h
(41)
79%
F F
CBr2F2, PPh3, KF
(42)
55%
7 Dihalo Alkanes
F F
F Cl
(CF3)3PF2, 120 °C, 24 h
F Cl (43)
Cl Cl
Cl Cl
One of the most useful reagents for generating di~uorocarbene is phenyltri~uoromethylmercury
�61ACR54�^ an example of its use is the addition of di~uorocarbene to benzobarrelene "Equation
"33## �68TL0802�[ One of the earliest methods used to generate di~uorocarbene was pyrolysis of the
sodium chlorodi~uoroacetate �59PCS70\ 53TL0350�^ it has been used to add to a double bond "Equa!
tion "34## �62TL0208�[ The hindered base\ sodium bis"trimethylsilyl#amide\ has been used to generate
di~uorocarbene from chlorodi~uoromethane[ The di~uorocarbene reacted with a malonate anion
to give an addition product "Equation "35## �74TL1334�[
PhHgCF3
(44)
F
F
O
O
O
O
F2ClCCO2Na, DIGLYME, reflux
(45)
F O
O F
F
CO2Et
CHClF2, NaN(TMS)2 (3 equiv.) F CO2Et
N CO2Et (46)
N CO2Et
Ph
Ph
3[90[1[6 Di~uoro Alkanes from Aldehydes and Ketones
Sulfur tetra~uoride was the _rst reagent used to convert aldehydes and ketones into ‘em!di~uoro
alkanes[ Two excellent reviews cover the use of sulfur tetra~uoride �63OR"10#0\ 74OR"23#208�^ a few
examples will be given here to highlight the advantages and disadvantages[ Aldehydes and ketones
with a!hydrogen atoms need to be treated at low temperatures for long periods to prevent decompo!
sition as shown in Equations "36# and "37# �60JOC707�[ Aromatic aldehydes "Equation "38## �60T834�
and higher temperatures\ generally 049�199>C\ give much higher yields[ Formaldehyde "in the form
of paraformaldehyde# at a high temperature "049>C# gave only a modest yield "Equation "49##
�59JA432�[
O
F F
SF4, CH2Cl2, 30 °C, 120 h
(47)
39%
O F F
SF4, CH2Cl2, 30 °C, 48 h
(48)
70%
F F
CHO
SF4, 150 °C, 6 h
(49)
F
F