Cyclopropenones reactions with enamine

The rather complex reactivity exhibited by cyclopropenones on interaction with enamines (see p. 74) is not re-found in the reactions of triafulvenes with enamines and ketene acetals. Instead of a (3 + 3) cycloaddition of enamine C=C—N sequence to the CI(2)/C3 bond of triafulvene (as represented by ylide 51 J) the addition of the enamine double bond to triafulvene C /C2 bond (operating with cyclopropenones only as a minor side-reaction) predominates in all reactions hitherto investigated. 

Treatment of cyclopropenones with isonitriles [56] [57] and of triafulvenes with isonitriles [58] gives cyclobutenes. Formations of expanded rings are observed by the reactions of enamines with diphenylcyclopropenones [59] [60]. 

In several synthetic studies, cyclopropane derivatives were used as synthones or building elements for ring enlargement steps, e.g. reaction of enamines with cyclopropenone [65], synthesis of 2,3-dihydro-l,4-diazepine by thermal isomerization of 1,2-diamino-cyclopropanes [32] [66], and preparation of 3-amino-fulvenes from methylencyclopropenes with alkynamines [67]. 

Fairly extensive studies have been reported on the reactions of enamines and other electron-rich multiple bonds with cyclopropenones. The reader is referred to the excellent review of Eicher and Weber for an exhaustive discussion of this area . ... 

Reaction of enamines with cyclopropenones produced penta-2,4-dienamide derivatives by cyclopropenone insertion into the enamine C-N bond (Table 1). ... 

Condensation of phenylcyclopropenones with enamines affords azabicyclo[3,l,0] hex-3-en-3-olates (714X which isomerize thermally to dienamides (715), the net reaction being an insertion of the ring-opened cyclopropenone into the nitrogen-... 

Miscellaneous Cycloadditions. The major reaction of alkyl- and aryl-substituted cyclopropenones with enamines to give amides involves formal C-1—C-2 bond cleavage of the cyclopropenone with cycloaddition to the enamine to give an initial dipolar intermediate (430). This mechanism also accounts for minor products. Work was extended to include reactions of enamines with diphenylcyclopropenethione and a re-evaluation of earlier evidence concerning reactions of diphenylcyclopropen-one and -thione with keten acetals. ... 

The bicyclic enamine 383 deviates from the above reaction scheme when interacting with diphenyl cyclopropenone the betaine 384 formed initially does not iso-merize to the amide 385, but to the a-amino cyclopentenone 386, possibly favored by steric reasons248. ... 

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