Abstract
Highly selective reactions using organo early transition metal compounds open several novel strategies for the construction of various organic compounds. Alkynylytterbium dichlorides, obtained by transmetallation from the corresponding Grignard reagents, showed reversal diastereoselectivity towards the acyl group in optically active 2-acyl-1, 3-oxathianes. Samarium diiodide-mediated Reformatsky-type reaction of α-halo esters with above 2-acyl-1, 3-oxathianes showed high diastereoselectivity and opens a new access to optically active β-hydroxy esters. Reduction of α-halo esters with SmI2 affords 4-metallo-3-oxobutanoate which reacts with aldehyde at C-4 position selectively to give 5-hydroxy-3-oxoalkanoic esters. Low valent tantalum reacts with alkynes to give alkyne-tantalum complexes. In-situ generated complexes can be used for the reaction with various electrophiles without purification. The reactivity of the complexes can be understood as a cis-ethene dianion equivalent. The complexes can be applied to the stereoselective synthesis of allylic alcohols, α, β-olefinic esters and amides, as well as 1-naphthols.
