Photoinduced Double Addition of Acetylene to 3-Oxocyclopent-1-ene-1-carbonitrile or 3-Oxocyclopent-1-enyl Acetate Leading to 2,3-Dihydro-1H-inden-1-one and Other Rearranged Products

Article abstract of DOI:10.1002/hlca.19880710704

UV Irradiation of 3-oxocyclopent-1-enyl acetate (17) and acetylene in MeCN at 0 deg C gives, besides the product of normal enone-alkyne <2 + 2> cycloaddition (cis-4-oxobicyclo<3.2.0>hept-6-en-1-yl acetate, 18) and its product of oxa-di-?-methane rearrangement (5-oxotricyclo<4.1.0.0^2,7>hept-2-yl acetate, 19), unexpected products of further addition of a molar equivalent of acetylene.These are indanone (= 2,3-dihydro-1H-inden-1-one, 16), in 21percent yield, cis-1-cisoid-1,2-cis-2- (20) and cis-1-transoid-1,2-cis-2,7-oxotricyclo<4.3.0.0^2,5>non-3-en-1-yl acetate (21), 4-oxo-7-'exo'-vinyltricyclo<3.2.0.0^2,6>hept-2-yl acetate (22), cis-4-oxo-6 -'endo'- (23) and cis-4-oxo-6-'exo'-vinylbicyclo<3.2.0>hept-1-yl acetate (24), and cis-4-oxo-7-'exo'-vinylbicyclo<3.2.0>hept-1-yl acetate (25).At least in part, indanone must be formed via intermediates 20 and 21.In fact, on heating a 9:1 mixture 20/21, indanone is obtained quantitatively.With 3-oxocyclopent-1-ene-1-carbonitrile (15) in place of 17, indanone is formed in lower (8percent) yield besides much tars.