Cyclopropenones electrophilic addition

In the course of mechanistic studies it was established that aniline does not react with the cyclopropenones (153 and 154) even under reflux conditions. It was therefore assumed that the formation of (158) involves initial nucleophilic attack by the aminopyridine ring nitrogen on the electrophilic cyclopropenone ring. In this way 155 is formed, which is then transformed via the reactive intermediates (156, 157, and/or 161) to the prodticts. Kascheres et al. noted that the formation of 157 is formally a stereospecific trans addition of the 2-aminopyridines to the double bond of the cyclopropenone (153). Such sterospecificity has been observed in kinetically controlled Michael additions. 

The reactions of cyclopropenone with a wide variety of reagents have been reported by Breslow, Oda, and Pecoraro. " Bromine gives an acyclic product after initial electrophilic attack at the carbonyl oxygen rather than at the double bond. As expected, triethyloxonium tetrafluoroborate gives ethoxycyclo-propenium tetrafluoroborate, and trifluoroacetic acid opens the C-1—C-2 bond, but this could conceivably occur after initial addition to the C-2—C-3 double bond. A cyclopropenyl cation is also a proposed intermediate in the... 

Diol (1) is used to prepare cyclopropenone acetal (2). Its highly nucleophilic double bond forms addition products with alcohols and amines and cycloaddition products with dienes to give norcarenes, ketones to give furanones and oxetanes, aldehydes to give butenolide, furan, and y-keto ester derivatives (eq 2), electrophilic alkenes to give cyclopropanes and functionalized cyclopentenones, and an a-pyrone to give a... 

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