Ligand-deficient catalysis enantioselective reaction

Remarkable chemoselectivity was also observed when alkyne-tethered electron-deficient olefins 158 were employed as substrates (Scheme 8.44) [123]. Rhodium/ diene catalysis led preferentially to carborhodation of the alkyne, followed by 1,4-addition to the a,P-unsaturated moiety to provide adducts 159 in high yield and excellent enantioselectivity. The difference between phosphines and chiral dienes as ligands in this reaction setting was striking. Whereas, rhodium-bisphosphines complexes catalyzed the 1,4-addition to a,P-enoates more effectively than the aryla-tion of alkynes, rhodium/diene catalysts favored the arylation of alkynes over the 1,4-addition. 

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