cesium pivalate, a mixture of spirooxindoles 41 and 42, as well as benzazepine 39,
is produced, suggesting the intermediacy of 41 in the reaction pathway. However,
similar to the control reaction performed in the former Fagnou’s report (Scheme 6),
41 was fully recovered when submitted to the optimized reaction conditions. In
contrast to other uses of Ag(I) salts as halide sequesters or oxidants, the authors
highlight the employment of exactly 1 equiv. Ag
+ as a halide abstractor to provide a
reactive cationic Pd species.
The proposed mechanism involves an initial oxidative addition (step A,
Scheme 9), followed by halide abstraction by the silver ion to provide a highly
reactive cationic Pd species (step B). Acetate-mediated CMD (step C) provides a
rare seven-membered ring palladacycle which undergoes ring opening (step D),
followed by deprotonation/reductive elimination (step E) to provide the desired
products.
Scheme 8 Synthesis of benzo[c]azepine-1-ones, (a) optimized reaction conditions, (b) pivalatepromoted reaction
Scheme 9 Plausible
mechanism for the
formation of benzo[c]
azepine-1-ones
98
D. Sustac Roman and A.B. Charette