Reaction development and mechanistic investigation of rhodium-catalyzed pyridine synthesis via C-H activation
Described herein are two complementary rhodium-catalyzed methods for the synthesis of substituted pyridines from unsaturated oxime derivatives and alkenes. In the first, formal [4+2] cycloaddition of O-pivaloyl α, β-unsaturated oxime esters and activated terminal alkenes was discovered to proceed in high yields and with excellent selectivity for 6-substituted pyridine products. Mechanistic experiments were found to be consistent with a reversible C-H activation step and a C-N bond forming, N-O bond cleaving process en route to pyridine formation. Rhodium-catalyzed coupling using unactivated ...
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