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-phenylcycl opropyl, 2,2-dimethylcyclopropyl, trans-2,3-dimethylcyclopropyl, cis-2 ,3-dimethylcyclopropyl, bicyclo[4.1.0]heptyl (1a-o, 6a,m, 11a,m)] in c hloroform results in photooxidation of the metal carbynes. Further rea ctions of the 17-electron carbyne complexes ultimately form cyclopente nones. Conversion of the 2-phenyl- and 2-ethylcyclopropyl carbyne comp lexes 1c,d occurs regiospecifically to yield 4-phenyl- and 4-ethylcycl opentenone (14c,d), respectively. Complexes bearing 2,3-dimethylcyclop ropyl substituents (1g-n) undergo an initial photochemical isomerizati on prior to oxidation and formation of the trans- and cis-4,5-dimethyl cyclopentenones (14g,i). The intermediate cyclopentenone complex CpCl[ P(OMe)3]MoL (L = trans-4,5-dimethylcyclopentenone) (15m) has been isol ated 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)degre es; V = 1671.1(5) angstrom3; Z = 4; R = 3.4%; R(w)= 4.3% for 2187 refl ections I > 0.01sigma(I).