ISSN:
0018-019X
Keywords:
Chemistry
;
Organic Chemistry
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
Notes:
The Aminal-enamine Equilibrium in Cyclopropane-carbaminals.The following cyclopropane-carbaminals were synthesized: N,N′-(T-2,t-3-dimethyl-r-1-cyclopropyl)methylene-dipyrrolidin (15), the corresponding (c-2, c-3)-isomer 16, N,N′-(cyclopropyl)methylene-dipyrrolidin (17) and N,N′-(c-2, t-3-diphenyl-r-1-cyclopropyl)methylene-dipyrrolidin (18). Their constitutions and configurations were derived from the method of synthesis and from 1H-NMR.-spectra. The c-c-r-1-dimethyl-aminal 16 rearranged at room temperature to its t-t-r-1-dimethyl-isomer 15. This demonstrates the existance of an aminal-enamine equilibrium for cyclopropane-carbaminals although cyclopropane-carbenamines have not been isolated as yet. The kinetic data found for the rearrangement of 16 to 15 are compatible with two mechanisms: In the first one, the protonated aminal 21 decomposes into the iminium-ion 22, which, in turn, yields the enamine 19. In the second one, 21 is converted to 19 in a single step. The formation of cyclopropyl-pyrrolidino-acetonitrile (26) and dipyrrolidino-ethylene-1,1-dicarbonitrile (27) from the reaction of the aminal 17 with tetracyanoethylene may also be explained with an aminal-enamine equilibrium. - This equilibrium lies strongly on the side of the aminal. Investigations of the aminal-enamine ratio of several cycloalkanecarbaminals, namely of the 3-ring derivative 17, the 4-ring derivative 35 and the bicyclic 5-ring derivative 38, show that ring strain is a determining factor for the equilibrium bias. This strain may also explain that the aminomethanol 41 was isolable.Some of the aminals were synthesized from previously unknown aldehydes. t-2, t-3-dimethyl-r-1-cyclopropane-carbaldehyde (11) and its (c-2, c-3)-isomer 12 were obtained by stereoselective ring-contraction of the 2-chloro-cyclobutanols 46 and 48/49, respectively. The configurations of the aldehydes 11 and 12, of the starting cyclobutanones 44 and 45 and of the cyclobutanol 46 were established by 1H-NMR. measurements. From the steric course of the ring contraction it can be concluded that it is the fastest rearrangement of 2-halo-cyclobutanols with base, when the conformation having an equatorial halogen atom is not obstructed. c-2, t-3-diphenyl-r-1-cyclopropane-carbaldehyde (14) and 3-phenyl-1-cyclobutane-car-baldehyde (34) were synthesized by reduction of the corresponding ester 50 and acid 52, respectively, followed by Sarett-oxidation.
Additional Material:
2 Tab.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/hlca.19770600532
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