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Chemistry of enamines II The structure of the pyrrolidine enamine of 2-methylcyclohexanone

✍ Scribed by Sudarshan K. Malhotra; Francis Johnson

Publisher
Elsevier Science
Year
1965
Tongue
French
Weight
253 KB
Volume
6
Category
Article
ISSN
0040-4039

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✦ Synopsis

The position isomer (I), having a trisubstituted double bond was originally assigned by Stork and associates to the structure of the pyrrolidine enamine of a substituted cyclohexanone. The tetrasubstituted ethylenic isomer II which was excluded on the basis of N.M.R. spectrum, involves steric interference between the substituent R and the methylene adjacent to nitrogen, if an overlap between the electron pair on nitrogen and the double bond is to be maintained2. Johnson and Whitehead have recently demonstrated that even the isomer I suffers from ;a (R = C&) similar steric interaction when the substituent R is quasi-equatorial. This interaction, however, vanishes when R is quasiaxially oriented. An inspection of the models confirms this LJ R b ::a (R = CHs) conclusion. Consequently it is to be expected that the alkylation of isomer I would occur from an axial direction, in view of toe necessity r^or continuous p-orbital overlap in the transition state, and t&.s would be subject to 1,3-diaxial interactiona.

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