Physical Organic Chemistry

217 Pages·1988·2.906 MB·English

by  G. Boche, G. Kaupp, E. Masimov, M. Rabinovitz, B. Zaslavsky (auth.)

641
Topics in Current Chemistry
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With 12 Figures and 72 Tables
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Editorial Board
Prof. Dr. Michael J. S. Dewar Department of Chemistry, The University of Texas
Austin, TX ,21787 USA
Prof. Dr. Jack D. Dunitz Laboratorium ffir Organische Chemic der
Eidgen6ssischen Hochschule
eBartssti/tigrevinU ,8(cid:127)6 CH-8006 Ziirich
Prof. Dr. Klaus Hafner Institut ffir Organische Chemic der TH
e3lartsnesreteP ,51 D-6100 Darmstadt
Prof. Dr. Edgar Heilbronner Physikalisch-Chemisches Institut der ti~tisrevinU
eBartsgreblegnilK ,08 CH-4000 lesaB
Prof. Dr. Sh6 It6 Department of Chemistry, Tohoku University,
Sendai, Japan 089
Prof. Dr. Jean-Marie Lehn Institut de Chimie, Universit6 de Strasbourg, ,1 rue
esialB Pascal, .B .P Z 296/R8, 80076-F Strasbourg-Cedex
Prof. Dr. Kurt Niedenzu University of Kentucky, College of Arts and secneicS
Department of Chemistry, Lexington, KY ,60504 USA
Prof. Dr. Kenneth N. Raymond Department of Chemistry, University of California,
,yelekreB California ,02749 USA
Prof. Dr. Charles W. Rees Hofmann Professor of Organic Chemistry, Department
of Chemistry, Imperial College of ecneicS and Technology,
South Kensington, London 7WS 2AY, England
Prof. Dr. Fritz V6gtle Institut fiir Organische Chemic und eimehcoiB
der ,ti~tisrevinU Gerhard-Domagk-Str. ,1
0035-D Bonn 1
Table of Contents
stnemegnarraeR of "snoinabraC"
G. Boche . . . . . . . . . . . . . . . . . . . . . .
Complex Eliminations; Eliminations with stnemegnarraeR
G. Kaupp . . . . . . . . . . . . . . . . . . . . . . 57
Polycyclic Anions: From Doubly to Highly Charged
~-Conjugated Systems
M. Rabinovitz . . . . . . . . . . . . . . . . . . . . 99
Methods of Analysis of the Relative Hydrophobicity of
Biological Solutes
B. Y. Zaslavsky, E. A. Masimov . . . . . . . . . . . . 171
Author Index Volumes 101-146 . . . . . . . . . . . . . 203
Rearrangements of "Carbanions"
Gernot Boche
Fachbereich Chemie der Philipps-Universit~it Marburg, Hans-Meerwein-Stral3e,
D-3550 Marburg, FRG
Table of Contents
1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
2 Rearrangements Involving Three-Membered Rings . . . . . . . . . .... 3
2.1 Cyclopropyl-Allyl-"Anion" Rearrangements . . . . . . . . . . . . 3
2.2 Allyl-"Anion" Isomerizations . . . . . . . . . . . . . . . . . . 7
2.3 Electron Transfer Induced Rearrangements of Cyclopropanes
and Consecutive Reactions . . . . . . . . . . . . . . . . . . . 01
2.3.1 Cyclopropanes Substituted with Carbonyl Groups . . . . . . . 1 I
2.3.2 Cyclopropanes Substituted with Phenyl(Aryl) Groups ..... 21
2.3.3 Other Examples . . . . . . . . . . . . . . . . . . . . . . 14
2.3.4 Trimethylene Radical "Anions" as Intermediates in
Cyclopropane Isomerizations and Transformations into
Isomeric Olef'ms . . . . . . . . . . . . . . . . . . . . . 71
2.3.4.1 Electron Transfer Catalyzed Stereoisomerization .... 71
2.3.4.2 Electron Transfer Initiated Formation of Isomeric Olef'ms 12
2.3.5 Proton Transfer or Electron Transfer Initiated Rearrangements
of Cyclopropanes in the Presence of a Base . . . . . . . . . . 12
3 Rearrangements Involving Four-Membered Rings: Electron Transfer Induced
Reductive Rearrangements of the Generalized Cyclobutene/Butadiene Radical
"Anion" System . . . . . . . . . . . . . . . . . . . . . . . . . . 23
4 Cyclization of 5-Hexenyl "Anions" . . . . . . . . . . . . . . . . . . 27
5 Configurational lsomerization of a-Substituted Vinyl "Anions" . . . . . . 31
5.1 ~-Aryl-Vinyllithium Compounds . . . . . . . . . . . . . . . . . 13
5.2 ~-Trimethylsilyl- and ~-Alkoxy-Vinyllithium Compounds ...... 33
6 The Reversible Rearrangement of Acyl-Substituted [9]Annulene "Anions" into
Nonafulvenolates as a Function of the Ion Pair Character . . . . . . . . 34
Topics in Current Chemistry, Vol. 641
© Sprirtger-Verlag, Berlin Heidelberg 8891
Gernot Boche
7 Electron Transfer Valence Tautomerism . . . . . . . . . . . . . . . . 37
8 Polymorphism of Organolithium Compounds . . . . . . . . . . . . . . 38
9 Rearrangements of and within Alkyllithium Aggregates . . . . . . . . . . 40
9.1 n-Butyllithium . . . . . . . . . . . . . . . . . . . . . . . . . 42
9.2 Phenyllithium . . . . . . . . . . . . . . . . . . . . . . . . . 43
9.3 tert-Butyllithium and tert-Pentyllithium . . . . . . . . . . . . . . 44
10 "Carbanion"-Accelerated Rearrangements . . . . . . . . . . . . . . . 45
11 Conclusions and Outlook . . . . . . . . . . . . . . . . . . . . . . 49
12 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50
After a brief introduction "carbanion" and "carbanion" radical rearrangements are reviewed with
special concern to the literature of the last ten years. Radical "anion" systems are included because
of the increasing importance of electron transfer reactions.
The first topic deals with the cyclopropyl-allyl and the intimately related allyl "anion" rearrange-
ment. Next, electron transfer induced rearrangements of cyclopropanes (stereoisomerization and
formation of ring-opened derivatives via trimethylene radical "anions") are reviewed. Inr elation with
this subject the question is discussed whether the rearrangement of cyclopropanes in the presence
of a base is initiated by proton or electron transfer. Section 3 deals with electron transfer induced
rearrangements of the generalized cyclobutene-butadiene radical "anion" system, followed by the
cyclization of 5-hexenyl "anions". Because of the widespread use of 5-hexenyl radical cyclizations as
a mechanistitco ol it is important to separate the radical from the "anion" rearrangement. Section 5
deals with the isomerization of c~-substituted vinyllithium compounds. Section 6 describes how the
structure ofa "carbanion" is strongly influenced by a variation of tgheeg enion, the solvent, complexing
agents and the temperature. Electron transfer valence isomerizations are treated next. The complexity
of"carbanion" structures in solution, as shown in sections 6 and 7, is also observed in the solid state
as demonstrated by the poIymorphism of organotithium compounds. Section 9 is devoted to some
results concerning rearrangements of and within alkyllithium aggregates, and the final topic refers
to "carbanion"-accelerated rearrangements.
stnemegnarraeR of"Carbanions"
1 Introduction
The literature on rearrangements of "carbanions" published up to 1979 has already
been reviewed I-8). Sigmatropic rearrangements and other migrations of saturated
groups (hydrogen, alkyl groups, hetero-atoms), unsaturated carbon (olefins, acetylenes,
aromatic compounds) and doubly bonded oxygen species (homoenolization, Favorskii
rearrangement, Ramberg-B~icklund reaction) are treated especially in the articles of
Grovenstein )6 and Hunter, Stothers and Warnhoff .)8 Electrocyclic reactions have
been extensively reviewed by Staley ,)5 Buncel )3 and Hunter )4
Most of the literature on rearrangements of "carbanions" reviewed in this article
has been published since 1979. Since "carbanions" normally neither exist in solution
(nor in the solid state), and since the gegenion, the solvent and chelating agents
strongly influence the structure and the reactivity of a certain (alkali or alkali earth)
organometallic compound, we stress those influences whenevetrh ere is information in
the literature. Furthermore, since it has been possible in recent years to characterize
different aggregates of organolithium species, their intra- and inter-"molecutar"
rearrangements and their different reactivities we included these results into this
article, too. Thus, we would like to emphasize the importance of non-skeletal rear-
rangements of"carbanions". Similarly, we have summarized rearrangements of radical
"anions" induced by electron transfer reactions because of the increasing importance
of this type of reaction lately.
2 Rearrangements Involving Three-Membered Rings
2.1 Cyclopropyl-Allyl-"Anion" Rearrangements
It was only after Woodward and Hoffmann had predicted a conrotatory mode for
the thermal cyclopropyl-allyl anion transformation in 1965 )9 that new interest develop-
ed in this reaction lo). But it was first shown by Huisgen and coworkers )11 by means
of the iso-rc-electronic uncharged aziridine 1 which gives the azomethine ylids 2 and
3, respectively, that the stereochemistry of the thermal and the photochemical reac-
tions agrees with the prediction.
p-3HCO4H6C
p-3HCO4H6C
-3HCO~HsC p
H C...._,~N 02 3HC hv £_C203HC ~. Hz
C~c~N,~/C H302 C 3H020
C203HC H H C02CH3 ¢onrot. I I
H H
3 1
2
Li + ÷ Li ÷ Li
,o-°ooc
conrot. ..~h Ph
hP H IF H
5 6
Gernot ehcoB
Kauffmann and coworkers )21 studied another hetero-analogous but in this case
an "anionic" system, N-lithio-cis-2,3-diphenylaziridine (4). 4 transforms thermally
into endo,exo-l,3-diphenyl-2-azallyllithium (5).
The rearrangement of 5 to 6 competes successfully with the trapping of 5 with
trans-stilbene which established the stereochemistry of 5. The stereochemistry of
2 and 3 has similarly been determined by 1,3-dipolar cycloaddition reactions.
Why is it that the predicted modes of rearrangement were first confirmed by means
of these two systems and not with a "real" cyclopropyt-altyl "anion" system ? The long
history of the cyclopropyl-allyl "anion" rearrangement shows that this is because
of several problems .)u01 The first of these, which is also indicated from the results
with 1 and 4, and which is confirmed by MO calculations, is the slow thermal conrota-
tion of a cyclopropyl "anion" to give the corresponding allyl "anion", as compared
to the fast isomerization of the allyt "anion" to give the most stable isomer.
Table 1 gives the results of several MO calculations for the conrotatory ring-opening
of the cyclopropyl anion to give the allyl anion, and of the isomerization of the allyl
anion )3~
Table .1 energies Relative ,rHAA( kcal/mol) with tcepser
to eht anion cyclopropyl of eht transition state of eht
conrotatory anion cyclopropyl-allyl rearrangement ,A
the allyl anion ,B and the transition state of the allyl
anion isomerization .C
A B C
MINDO/3 2.13 --9.8 --
G3-OTS 7.66 --9.7 3.52
G13-4 0.83 --40.0 6.72
It is e4ident from Table 1 that the "activation energy" for the allyl anion isomeriza-
tion is much lower than for the conrotation of the cyclopropyl anion to give the allyl
anion. Consequently, in order to verify the'predicted conrotatory mode one has to
trap the first formed allyl "anion" before it isomerizes to give the thermodynamically
most stable isomer, e.g., in a cycloaddition reaction. Exactly this was possible with
2, 3 and 5. So far, however, a similarly fast reaction has not been found for allyl
"anions" )31
The second problem is concerned with the question of which organometallic com-
pounds behave like cyclopropyl "anions" and undergo such a ring-opening reaction.
Interestingly, no ring-opening reaction has been observed, e.g., with cyclopropylli-
thitma 7 )41 and 1-cyano-2,2-diphenylcyclopropyllithium 8 .~5~ On the other hand,
1,2,3-triphenylcyclopropane reacts with n-butyUithium/tetramethylethylene diamine
(TMEDA) to give a mixture of isomers of 1,2,3-triphenylallyllithium which indicates
that the intermediately formed 1,2,3-triphenylcyclopropyllithium 9 is able to undergo
a ring-opening reaction ~)
4
stnemegnarraeR of "Carbanions"
iL ÷
Ph/ H Ph
7 8 9
If one compares ,7 8 and 9 (and many more cyclopropyl "anions") lob) it turns out
that electron acceptor substituents at both carbon atoms, which become terminal
centers of the allyl "anion", facilitate the ring scission. In addition it is necessary that
the negative charge of the cyclopropyl "anion" is stabilized by electron withdraw-
ing (!) groups ; hydrogen or alkyl groups at C-1 render the ring-opening reaction more
difficult or impossible. This, of course, is quite the opposite to what one would expect
if a real cyclopropyl anion were the ring-opening species. Thus, ion pair effects play
an essential role in the rearrangement of cyclopropyl "anions".
In spite of these difficulties a kinetical criterium has been elaborated for the thermal
conrotation ofa cyclopropyl "anion". The result of this study has recently been con-
firmed by a special cyclopropyl-allyl "anion" rearrangement allowing trapping reac-
tions of the altyl "anion".
In their kinetic studies, Boche and coworkers )v1.31 first examined the rates of
the ring-opening reactions of the isomeric 1-cyano-2,3-diphenylallyllithium com-
pounds 10 and 14, and of the isomerization reactions of the 1,3-diphen3~l-2-cyano-
allyllithium species (11 ~- 12 ,-~ 13).
CN ki ÷
H Ph
co or.
I disrot.
I
i
Li*CN NC Li÷ NC Li÷
Ph Ph Ph 41 H H
11 21 31
,,"~ f .tornoc / .
,\'.d torsi .torsld'/
"-, H 2s H CN Li" ."
Ph Ph
It was shown that the ring-opening reaction e.g. of 10 to give 13 (and/or 11 which
is not clear from the available data) is about 1500 times slower than the isomerization
of the allyl "anion" 13 (and/or 11) to give the more stable 12. A similar situation occurs
when one startg from the cyclopropyl "anion" 14 .~81 These experimental data thus
nicely confirm the results of the theoretical calculations discussed in connection with
Table .1