ISSN:
0018-019X
Keywords:
Chemistry
;
Organic Chemistry
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
Notes:
The pyrrolidino-aminal (4) of bicyclo[3.1.0]hex-2-ene-6-endo-carbaldehyde (3) underwent a facile (80°), mildly acid catalyzed isomerization to the corresponding exo-aminal (6), which was characterized by hydrolysis to bicyclo[3.1.0]hex-2-ene-6-exo-carbaldehyde (7).At higher temperatures (140°), the two aminals 4 and 6 were converted smoothly to a 1:1 mixture of syn- and anti-4-(pyrrolidino-methylidene)-bicyclo[3.1.0]hex-2-ene (syn- and anti-7-pyrrolidino-homofulvene1) 8 and 9. The structures of 8 and 9 were derived from spectral data. This corrects a previous interpretation by Cook et al.The endo → exo-aminal isomerization (4 → 6) is considered to occur via the enamine (5) of bicyclo[3.1.0]hex-2-ene-6-carbaldehyde (3 or 7), with which the aminals (4 and 6) are in equilibrium. The same enamine (5), a methylidene cyclopropane derivative, is thought to be the intermediate in the aminal (4 or 6) → amino-homofulvene (8 and 9) conversion, which, therefore, belongs to the vinyl-methylidene-cyclopropane rearrangement type.A cationic mechanism for the endo → exo-aminal isomerization is excluded by the discrepancy in this reaction of the pyrrolidino-aminals (13 and 15) of 6-exo-methyl-bicyclo[3.1.0]hex-2-ene-6-endo-carbaldehyde (12) and of bicyclo[3.1.0]hexane-6-endo-carbaldehyde (14). While the former aminal (13) is stable even under acid catalysis and at higher temperatures, the latter (15) isomerizes readily to the exo-aminal 16.The three endo-aldehydes 3, 12 and 14 were prepared by the alkali catalyzed rearrangement of the three chlorohydrins 7-endo-chloro-bicyclo[3.2.0]hept-2-en-6-endo-ol (20ac), 7-endo-chloro-7-exo-methyl-bicyclo[3.2.0]hept-2-en-6-endo-ol (20ad) and 7-endo-chloro-bicyclo[3.2.0]heptan-6-endo-ol (20bc) according to the method of Brook.The configurations of the unsaturated endo-aldehydes 3 and 12 followed from their equilibria with the corresponding 2-oxa-bicyclo[3.2.1]octa-3,6-diene systems (23) and those of the saturated aldehydes 14 and 17 from oxidations to the corresponding carboxylic acids. The endo- and exo- isomers of the aldehydes and aminals treated in this work were readily distinguished by certain highly characteristic NMR.-signals.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/hlca.19740570327
