Organic Reaction Mechanisms · 2008: An annual survey covering the literature dated January to December 2008

536 Pages·2011·4.95 MB·English

·
ORGANIC REACTION MECHANISMS 2008
Organic Reaction Mechanisms · 20 0 8 : An annual survey covering the literature dated January to December 2008 Edited by A. C. Knipe
© 2011 John Wiley & Sons, Ltd. ISBN: 978-0-470-74981-4
ORGANIC REACTION
·
MECHANISMS 2008
An annual survey covering the literature
dated January to December 2008
Editedby
A. C. Knipe
University of Ulster
Northern Ireland
®
AnInterscience Publication
A John Wiley and Sons, Ltd., Publication
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Contributors
S. K. ARMSTRONG Formerly attheDepartmentof Chemistry,Universityof
Glasgow, Glasgow G12 8QQ, UK
K. K. BANERJI Indra-Kripa, A-80 Saraswati Nagar, Jodhpur 342005,
India
C. T. BEDFORD Department of Chemistry, University College London,
20 Gordon Street, London, WC1H 0AJ, UK
M. L. BIRSA Faculty of Chemistry, “Al. I. Cuza” University of Iasi,
Bd. Carol I, 11, Iasi 700506, Romania
A. BRANDI Dipartimento di Chimica Organica “U. Schiff”, Univer-
sita’ degli Studi di Firenze-Polo Scientifico, Via della
Lastruccia 13 1-50019 Sesto Fiorentino (Fl), Italy
R. G. COOMBES Department of Chemistry, University College London,
20 Gordon Street, London, WC1H 0AJ, UK
M. R. CRAMPTON Department of Chemistry, University of Durham, South
Road, Durham, DH1 3LE, UK
N. DENNIS 3 Camphorlaurel Court, Stretton, Brisbane, Queensland
4116, Australia
M. GENSINI Menarini Ricerche S.p.A., Via Sette Santi, 3, 50131
Florence, Italy
A. C. KNIPE Faculty of Life and Health Sciences, University of
Ulster, Coleraine, Northern Ireland
P. KOCˇOVSKY´ Department of Chemistry, The Joseph Black Building,
The University of Glasgow, Glasgow G12 8QQ, UK
R. A. McCLELLAND Department of Chemistry, University of Toronto, 80
St George Street, Toronto, Ontario, M5S 1A1, Canada
M. G. MOLONEY Department of Chemistry, University of Oxford, Chem-
istryResearchLaboratory,MansfieldRoad,OxfordOX1
3TA, UK
v
Preface
Thepresentvolume,theforty-fourthintheseries,surveysresearchonorganicreaction
mechanisms described in the available literature dated 2008. In order to limit the size
of the volume, it is necessary to exclude or restrict overlap with other publications
which review specialist areas (e.g. photochemical reactions, biosynthesis, enzymol-
ogy,electrochemistry,organometallicchemistry,surfacechemistryandheterogeneous
catalysis). In order to minimize duplication, while ensuring a comprehensive cover-
age,theeditorconductsasurveyofallrelevantliteratureandallocatespublicationsto
appropriate chapters. While a particular reference may be allocated to more than one
chapter, it is assumed that readers will be aware of the alternative chapters to which
a borderline topic of interest may have been preferentially assigned.
In view of the considerable interest in application of stereoselective reactions to
organicsynthesis,wenowprovideindication,inthemargin,ofreactionswhichoccur
with significant diastereomeric or enantiomeric excess (de or ee).
Please note that the editor has written two chapters for this volume and Dr. M. G.
Moloney has kindly contributed as a guest author. These and other steps are aimed
to relieve pressure on continuing authors and thereby reduce progressively the delay
between title year and publication date. As a consequence, we expect to publish
severalORMvolumesatnine-monthintervalsuntilouroptimumproductionschedule
is regained.
I wish to thank the production staff of John Wiley and Sons and the team of
experienced contributors for their efforts to ensure that the review standards of this
series are sustained.
A. C. K.
vii
CONTENTS
1. Reactions of Aldehydes and Ketones and their Derivatives
by A. C. Knipe....................................................... 1
2. Reactions of Carboxylic, Phosphoric, and Sulfonic Acids and their
Derivatives by C. T. Bedford......................................... 45
3. Oxidation and Reduction by K. K. Banerji............................ 79
4. Carbenes and Nitrenes by M. G. Moloney............................ 129
5. Nucleophilic Aromatic Substitution by M. R. Crampton............... 153
6. Electrophilic Aromatic Substitution by R. G. Coombes................ 165
7. Carbocations by R. A. McClelland.................................... 183
8. Nucleophilic Aliphatic Substitution by A. C. Knipe................... 203
9. Carbanions and Electrophilic Aliphatic Substitution by M. L. Birsa... 225
10. Elimination Reactions by M. L. Birsa................................. 253
11. Addition Reactions: Polar Addition by P. Kocˇovsky´ .................. 267
12. Addition Reactions: Cycloaddition by N. Dennis...................... 331
13. Molecular Rearrangements: Part 1. Pericyclic Molecular
Rearrangements by S. K. Armstrong ................................. 361
14. Molecular Rearrangements: Part 2. Other Reactions by A. Brandi and
M. Gensini........................................................... 393
Author Index........................................................ 459
Subject Index....................................................... 491
ix
CHAPTER 1
Reactions of Aldehydes and Ketones
and their Derivatives
A.C.Knipe
Faculty ofLife andHealth Sciences,University of Ulster, Coleraine
Formation and Reactions of Acetals and Related Species . . . . . . . . . . . . . 2
Reactions of Glucosides and Nucleosides . . . . . . . . . . . . . . . . . . . . . . 2
Formation and Reactions of Nitrogen Derivatives . . . . . . . . . . . . . . . . . 3
Imines: Synthesis, Tautomerism, Catalysis . . . . . . . . . . . . . . . . . . 3
The Mannich and Nitro-MannichReactions . . . . . . . . . . . . . . . . . . 5
Addition of Organometallics . . . . . . . . . . . . . . . . . . . . . . . . . . 10
Oxidation and Reduction of Imines . . . . . . . . . . . . . . . . . . . . . . 11
Iminium Species . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
Imine Cycloadditions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
Other Reactions of Imines . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
Oximes, Hydrazones, and Related Species . . . . . . . . . . . . . . . . . . 14
C–C Bond Formation and Fission:Aldol and Related Reactions. . . . . . . . . 17
Regio-, Enantio-, and Diastereo-selectiveAldol Reactions . . . . . . . . . . 17
Intramolecular Aldols . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
Mukaiyama and VinylogousAldols . . . . . . . . . . . . . . . . . . . . . . 22
Nitrile/Nitro/NitrosoAldols . . . . . . . . . . . . . . . . . . . . . . . . . . 23
Other Aldol-typeReactions . . . . . . . . . . . . . . . . . . . . . . . . . . 24
Pinacol- and Benzoin-typeCoupling. . . . . . . . . . . . . . . . . . . . . . 25
The Baylis–Hillman and its Aza and MoritaVariants . . . . . . . . . . . . . 25
Allylation and Related Reactions . . . . . . . . . . . . . . . . . . . . . . . 27
Alkynations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
Michael Additions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
Other Addition Reactions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
General and Theoretical . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
Addition of Organozincs . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
Addition of Other Organometallics . . . . . . . . . . . . . . . . . . . . . . 30
Grignard-type Reactions . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
Hydrocyanation and Cyanosilylation. . . . . . . . . . . . . . . . . . . . . . 31
Hydrosilylationand Hydrophosphonylation . . . . . . . . . . . . . . . . . . 32
Miscellaneous Additions . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
Enolization and Related Reactions . . . . . . . . . . . . . . . . . . . . . . . . . 35
Oxidation and Reduction of Carbonyl Compounds . . . . . . . . . . . . . . . . 36
Regio-, Enantio-, and Diastereo-selectiveReduction Reactions . . . . . . . . 36
Oxidation Reactions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
Other Reactions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
References. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
Organic Reaction Mechanisms · 20 0 8 : An annual survey covering the literature dated January to December 2008 Edited by A. C. Knipe
© 2011 John Wiley & Sons, Ltd. ISBN: 978-0-470-74981-4
1
2 OrganicReactionMechanisms2008
Formation and Reactions of Acetals and Related Species
A water-soluble self-assembled host molecule [Ga L ]12− has been found to catalyse
4 6
the hydrolysis of orthoformates HC(OR) in basic solution with marked rate accel-
3
erations of up to 3900 (R=Pr) relative to the uncatalysed reaction.1 Enzyme-like
Michaelis–Menten kinetics apply and 13C labeling experiments have helped to estab-
lishthattheneutralsubstrateisencapsulatedinthehostintherestingstate;thisiscon-
sistentwiththemorenegativeentropyofactivationfoundforthecatalyticprocess.The
solvent isotope effects k(H O)/k(D O)=1.6 is indicative of an A-S 2 mechanism
2 2 E
withrate-limitingprotontransfer,incontrastwiththeA1mechanismforthecatalysed
reaction which involves rate-limiting decomposition of the protonated substrate.
Pyridiniumsaltderivativeshavebeenfoundtocatalyse(at0.1%loading)acetaliza-
tion reactions of both aldehydes and ketones in methanol at room temperature more
efficiently than Brønsted acids of pK =2.2.2
a
A study of the effects of the strength of the nucleophile (Nu-SiMe ) on the stereo-
3
chemicaloutcomeofsubstitutionreactionsofcyclicacetals(inCH Cl inthepresence
2 2
of Me SiOTf or BF OEt ) has revealed a continuum of mechanisms. Stereoselec-
3 3 2
tive S 1 mechanisms (via the oxocarbenium ion intermediate) occur with weak and
N
moderate nucleophiles and poor leaving groups, whereas strong nucleophiles adopt
unselective diffusion-limited S 1 and S 2 pathways.3
N N
A highly enantioselective(upto 99%ee) anddiastereoselectivealdol-type reaction
of β-keto esters with acetals has been achieved under the catalytic influence of chiral
cationicPd(II)–andPt(II)–binapcomplexeswhichcanactasacid/basecatalysts,with
simultaneous activation of both the nucleophile (as chiral metal enolate) and acetal;4
the enantioselectivity is apparently dependent on conversion of the acetal into the
oxonium ion, by protonation under the acidic conditions used.
ALewisbase-catalyseddiastereoselectiveandenantioselectiveglycolatealdolreac-
tion has been developed whereby a range of aldehydes can be converted to both syn-
and anti-1,2-diols under the same catalytic system by adjusting the size of the silyl
ketene acetal [R3OCH=C(OR2)OSiR1 ] used as the nucleophilic component; these
Mukaiyama-type aldol reactions are co3nducted in CH Cl at −78◦C in the presence
2 2
of SiCl , i-Pr NEt and a bisphosphoramide catalyst.5
4 2
The Brønsted acid catalysed aza-Ferrier reaction of N-Boc-2-(1,3-dienyloxy)
pyrrolidines has been found to proceed via heterolytic C–O cleavage to give the
iminium alkoxide, from which the corresponding α-(N-Boc-2-pyrrolidinyl)aldehyde
is formed in excellent yield and high α-regioselectivity by C–C bond formation.6
Reactions of Glucosides and Nucleosides
Nucleophilic substitution reactions of 2-phenylthio-substituted carbohydrate acetals
and related systems have been reviewed, with particular reference to episulfonium
ions vs oxocarbenium ions as reactive intermediates in stereocontrolled glycosylation
reactions.7
Mechanisticstudy(usingkineticexperiments,Hammetplots,DFTcalculationsand
11BNMR)ofregioselectiveboranereductiveopeningsofcyclicacetalshasestablished
1ReactionsofAldehydesandKetonesandtheirDerivatives 3
thattheoutcomedependsontheelectrophilewithwhichthemoreelectron-richoxygen
associates, and this can be altered by Lewis acid activation of the borane.8
Aplausiblemechanismhasbeensuggestedtoaccountforα-selectiveglucosylation
which allowed the synthesis of the tetrasaccharide [Glcα1→2Glcα1→3Glcα1→
3Man],enabledbythesynergisticeffectofcombinedetheralandhalogenicsolvents.9
Hydrolysis of toxic 7-hydroxycoumarin glucosides and other aryl and alkyl gluco-
sides catalysed by modified α- and β-cyclodextrin dicyanohydrins has been found to
follow Michaelis–Menten kinetics and to display rate increases of up to k /k =
cat uncat
7569 (for the hydroxycoumarin glucoside).10
ResultsofaDFTstudyofsuitableanalogueshaveexplainedtherelativeO(3)/O(4)
reactivities previously reported for reaction of glycosyl donors with both α- and β-
methyl glycosides of N-dimethylmaleoyl (DMM) glucosamine acceptors protected at
O(6).11 The preferential or exclusive substitution at O(3) for the α-anomers and at
O(4) for the β-anomers has been attributed to the different alignments for the DMM
ring: for the β-anomers the ring is parallel to the C(2)–H(2) bond for steric reasons,
whereas for the α-anomers it is tilted such that a strong hydrogen bond between one
of its carbonyl groups and HO(3) makes O(3) more reactive.
A study of potential neighbouring group participation by non-vicinal esters in
glycosylation reactions has found that glycopyranosylation is aided by intermedi-
ate formation of a 1,3-O-cyclic carbonate ester, with loss of a t-butyl cation from
a t-butoxycarbonyl ester group axially substituted at C(3), but that the correspond-
ing 3-O-equatorial, 4-O-axial and -equatorial, and 6-O carbonates do not undergo
intramolecular reaction under typical glycosylation conditions.12 Galactopyranosyla-
tion reactions of a 4-O-(2-carboxy)benzoate ester and a 4-O-(4-methoxybenzoate)
ester also failed to exhibit neighbouring group participation; this was particularly
clear for the latter, for which 18O quenching failed to detect bridging intermediates.
The unesterified hydroxyl groups were protected as benzyl ethers.
Formation and Reactions of Nitrogen Derivatives
Imines: Synthesis, Tautomerism, Catalysis
Isomerizationoftheiminederivedfrombenzylamineandtrifluoroacetophenonetothe
corresponding N-benzylidene-2,2,2-trifluoro-1-(phenyl)ethylamine has been found to
proceed by a concerted mechanism via a virtually unionized transition state when
catalysed by triethylamine in acetonitrile.13
Triarylmethyl chlorides have been used as efficient organic catalysts for synthesis
of N-sulfonylimines, via condensation of sulfonamides with aldehydes or ketones,
◦
under mild metal-free conditions at 40 C in neutral media; the carbonyl compounds
are believed to be activated by complexation with triarylmethyl cation.14
Individual equilibrium constants have been determined for the three steps whereby
o-phthalaldehyde [o-C H (CHO) ] reacts with ammonia to give an isoindole
6 4 2
derivative; cyclization of the initially formed carbinolamine intermediate to the
1,3-dihydroxyindole and subsequent imine formation by dehydration are both acid
catalysed; the concentrations of the intermediates are negligible at equilibrium and
the same applies for the corresponding reaction with 2-aminoethanol, for which
4 OrganicReactionMechanisms2008
initial formation of carbinolamine was too fast to measure by the combination of
spectrophotometric and polarographic techniques used.15
2-Fluoro-1,1-diphenylaziridines(1)havebeenfoundtoreactwitharylethynylborates
inthepresenceofBF ·OEt toformmonofluorinatedpropargylamines(5)in30–66%
3 2
yield, along with indoles (6) (Scheme 1).16 This modified Petasis reaction proceeds
by isomerization to α-fluorinated imines (3), which react with alkynyldifluoroborane
generated insitu from the potassium alkynyltrufluoroborates and BF ·OEt .
3 2
R
N
Ar
R R + LA R LA
N
N LA N (6)
Ph Ph Ph +
Ph F Ph F Ph F
(1) (2)
LA + R
N
Ph
H
Ph F
Ph BF2 LA
(3)
F F
H N R F2B N R B N+ R
aq. Na CO
2 3
Ph Ph Ph Ph
H
Ph F Ar Ph F Ar Ph F
(5) (4)
Scheme1
A study of the diastereoselectivity of the Pictet–Spengler condensation of trypto-
phan methyl ester (7) and α-aminoaldehydes (8) derived from l- or d-amino acids as
chiral carbonyl components has established that there is chirality transfer from C(2)
of the α-aminoaldehyde to the newly created stereogenic centre in the tetrahydro-
β-carboline derivative (9).17 The diastereomeric products (cis/trans) obtained from
various combinations of enantiomers of the chiral reactants were such that cis and
trans (65–100%) 1,3-disubstituted 1,2,3,4-tetrahydro-β-carbolines are formed (‘mis-
matched’ situation) from l,l or d,d combinations, whereas only the cis diastereomer
(‘matched situation’) is obtained from combinations of opposite configuration (l,d or