PHOTOCHEMISTRY OF ALPHA,BETA-UNSATURATED ESTERS .7. PHOTOLYTIC BEHAVIOR OF VINYLCYCLOPROPANE CARBOXYLATES

Upon direct photolysis esters 1-6 undergo the following reactions: fragmentation to carbenes (followed by their collapse to allenes, furans and cyclopropenes), rearrangement to cyclopentenes and ring expansion to bicyclo[2.1,0]pentanes. Ring opening to dienic esters and deconjugation, a reaction characteristic of simple α,β-unsaturated esters, are not important general pathways. In methanol-O-d double bond migration in 2 to give ethyl 3-cyclopropyl-3-butenoate (26) becomes the prominent reaction course. Sensitized photolyses yield only cyclopentenes. The photolytic course is strongly influenced by double bond substituents. Possible conformational origins of this effect and other mechanistic aspects of these reactions are considered. © 1969, American Chemical Society. All rights reserved.