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Selective palladium-catalyzed hydrogenolysis of propargylic alcohol 9, via its formate 10 or carbonate 13, gave up to 98% of alkyne 11. Alkyne allene selectivity is controlled by the steric bulk of the phosphine ligand, as well as the propargylic (C-22) and alkyne (C-24) substituents in the substrate. A steric ligand-substrate interaction in the intermediate π- propargyl allenyl palladium complexes is suggested to explain these effects.

Summary Oxazolidinone acrylamides undergo addition reactions with alkyl iodides and allyltributylstannane to give 1,3-substituted products with a threo preference in excess of 10:1. This threo preference is highest for reactions carried out in nonpolar solvents, a result consistent with dipolar stabilization of the transition state leading to the threo product.

In situ prepared ( Z )- and ( E )-1-alkenylzinc bromides 5 were added to various aldehydes 1 in the presence of lithiated (+)- N -methylephedrine or (+)-2-( N,N -dimethylamino)-1,2-diphenylethanol to give sec . allyalcohols 7 in high optical purity with simple recovery of the chiral aminol 6 .

The Red-Al ® reduction of 4-silyloxy propargylic alcohols to 4-silyloxy allylic alcohols involves two consecutive regio- and stereospecific 1,3 silyl migrations — from oxygen to carbon and then back to the original oxygen.

Readily available chiral tridentate ligand 8 catalyzes the highly Si-face selective addition of diethyl-, di-n-propylzinc and, more significantly, of divinylzinc to aromatic and aliphatic aldehydes whereas bidentate ligands 11 and 12 exert a topologically reversed catalytic bias.