REACTION OF CYCLOBUTENONES WITH LOW-VALENT METAL REAGENTS TO FORM ETA-4-VINYLKETENE AND ETA-2-VINYLKETENE COMPLEXES - REACTION OF ETA-4-VINYLKETENE COMPLEXES WITH ALKYNES TO FORM PHENOLS

The reactivity of cyclobutenones toward some low-valent transition-metal reagents has been investigated. Treatment of 3-substituted and 2,3-disubstituted cyclobutenones with ClRh(PPh3)3 led to eta(2)-vinylketene complexes Cl(PPh3)2 activated RhC(O)C(R1) = C(R2)CH2 (4). Complex 4e (R1 = H, R2 = C(O)C6H5) has been characterized by X-ray crystallography: triclinic, P1BAR (No. 2), a = 12.868 (4) angstrom, b = 13.158 (3) angstrom, c = 15.241 (4) angstrom, alpha = 81.49 (2)-degrees, beta = 79.45 (2)-degrees, gamma = 60.72 (2)-degrees, V = 2209 (1) angstrom 3, Z = 2. Treatment of ClRh(PPh3)3 with benzocyclobutenones gave mixtures of 2-rhodaindanones and 1-rhodaisoindanones. Reaction of 3-substituted and 3,4-disubstituted cyclobutenones with (eta(5)-C9H7)Co(PPh3)2 (9) gave eta(4)-vinylketene complexes (eta(5)-C9H7)Co(eta(4)-C(O) = C(H)C(R1) = CHR2) (10). Anti isomers of 10 were formed as the major kinetic products; isomerization to the syn isomer was observed in two cases. Reversible conversion of an eta(4)-vinylketene complex to the eta(2)-mode was induced by addition of PPh3 or CO to 10a (R1 = Ph, R2 = H). Structurally different metallacycles (eta(5)-C9H7)(PPh3) activated CoC(O)CH2C(R1) = CH (13) were obtained from 9 and cyclobutenones in the presence of ZnCl2. Upon treatment with alkynes, 10a gave a series of substituted phenols. Complex 10b (R1 = Ph, R2 = CH3) reacted only with dimethyl acetylenedicarboxylate to give both a phenol and an eta(4)-cyclohexadienone complex. Mechanisms are discussed for the insertion reactions of 9 and for the phenol-producing alkyne reactions.