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[reaction: see text] The palladium-mediated ring opening of substituted cyclopropanols has been found to take place predominantly at the less substituted C-C bond. Thus, sequential application of the titanium-mediated cyclopropanation of esters and the palladium-mediated ring opening of the resulting cyclopropanols provides a convenient method for functionalizing monosubstituted olefins.

Abstract:The reaction of [RuCl,(pybox)-(C,H,)] (1) (pybox = 2,6-bis[(4S)-isopropyloxazolin-2'-yl]pyridine) and 2,6-ditert-butyltolyl diazoacetate (4) (DBT-DA) in benzene at 50°C gave a stable 2,6 -di -tert -butyltolylcarbonylcarbeneruthenium complex 5 in 94% yield. The structure of 5 was characterized by NMR spectroscopy. 2,6-Diisopropylphenyl diazoacetate (6) and 2,4,6-trimethylphenyl diazoacetate (7) also gave the corresponding carbene complexes 9 and 10, respectively. Asymmetric carbene transfer from the carbene complexes to styrene resulted in formation of the trans isomer of phenylcyclopropanecarboxylates 2 with high enantioselectivity : 2 was obtained as the sole product in 80% yield (55% ee) from 5 at 80 "C and in 82 % yield (97 YO ee) from 9 at 60 "C; from 10 at 40 "C, a mixture of 2 and 3 in a ratio of 97:3 was formed in 91 740 yield (97% ee for 2 and 99 % ee for 3). After the carbene transfer reaction, the ethylene complex 1 could be regenerated and isolated by treatment of the reaction mixture under an ethylene atmosphere. The carbene complexes 9 and 10 (2 mol%) exhibited catalytic activity in the asymmetric cyclopropanation of styrene with the corresponding diazoacetates.

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