Cyclopropyl ketimines, rearrangement

The photochemical rearrangement of enamides to vinylogous amides was described (65],652). Rearrangement of cyclopropyl ketimines to enamines with acid was applied to syntheses of myosamine, apoferrosamine, mesembrine, and desmethoxymesembrine (653-656). 

Scheme 45. Preparation of heterocycles 138,141 via Cloke rearrangement of the cyclopropyl-ketimine moieties in 131,135 [60b]...

The dicyclopropyl ketimine 198 prepared from the 0,N-cyclopropanone hemiacetal 194 (vide supra, Sect. 4.9, Eq. (62)), heated in xylene with ammonium chloride for 4 hr underwent ring expansion exclusively to the enamine 399 followed by isomerization to the cyclopropyl pyrroline 400. Although further ring expansion was not observed on prolonged heating, 400 was converted to the hydrobromide 401 with anhydrous HBr 2091 which upon heating to 140 °C for 10 min experienced a second cyclopropyl imine rearrangement to provide the pyrrolizidone 403 in 51 % yield, most probably via the HBr adduct 401 by cyclization to the pyrroline 402 followed by acid-induced hydrolysis, Eq. (95) 129). 

The formation of pyrroles by the reaction of the cyclopropylketimine (63) with HBF4 has been studied from a mechanistic point of view using 3-chloropropionyl chloride enriched with at the carbonyl carbon atom The C-NMR spectrum of the pyrrole formed from the cyclopropyl ketimine (63) shows enhancement of the peak at the 5-carbon in accord with mechanism A outlined in Scheme 27. Operation of process B analogous to the vinylcyclopropane rearrangement 63a would have led to enrichment at the 3-carbon of the pyrrole product. 

Further cyclopropyl aryl ketimine rearrangements have been noted, and bicyclo[3,l,0]hex-3-enones undergo rearrangement via keten intermediates. ... 

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