REGIOSELECTIVE AND STEREOSELECTIVE FORMATION OF CYCLOPENTENONES UPON PHOTOOXIDATION OF CYCLOPROPYL CARBYNE COMPLEXES

Photolysis of the cyclopropyl carbyne complexes Cp(CO)LM=CR [M = W, Mo; L = CO, P(OMe)3, P(OPh)3; R = C3H5, 2-ethylcyclopropyl, 2-phenylcyclopropyl, 2,2-dimethylcyclopropyl, trans-2,3-dimethylcyclopropyl, cis-2,3-dimethylcyclopropyl, bicyclo[4.1.0]heptyl (1a-o, 6a,m, 11a,m)] in chloroform results in photooxidation of the metal carbynes. Further reactions of the 17-electron carbyne complexes ultimately form cyclopentenones. Conversion of the 2-phenyl- and 2-ethylcyclopropyl carbyne complexes 1c,d occurs regiospecifically to yield 4-phenyl- and 4-ethylcyclopentenone (14c,d), respectively. Complexes bearing 2,3-dimethylcyclopropyl substituents (1g-n) undergo an initial photochemical isomerization prior to oxidation and formation of the trans- and cis-4,5-dimethylcyclopentenones (14g,i). The intermediate cyclopentenone complex CpCl[P(OMe)3]MoL (L = trans-4,5-dimethylcyclopentenone) (15m) has been isolated and a crystal structure obtained: P2(1)/c; a = 14.101(3) angstrom; b = 9.516(2) angstrom; c = 13.497(2) angstrom; beta = 112.68(1)degrees; V = 1671.1(5) angstrom3; Z = 4; R = 3.4%; R(w)= 4.3% for 2187 reflections I > 0.01sigma(I).