Asymmetric Cycloaddition Using Coordination Ability of Heteroatom with Organometallics

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Heteroatoms in organic chemistry have become a powerful tool for asymmetric synthesis as a chiral ligand with organometals. We focused on the sulfur atom, incorporated a chiral molecule, which could coordinate with organometals. The aim of this resaerch project is thus to develope an addition reaction of such organometalic compounds as diethylzinc to an aldehyde in the presence of chiral camphor-derived ligands containing the sulfur as sulfides or sulfoxides. Furthermore, the effectiveness of a sulfinyl group in the beta-sulfinyl carbonyl compounds, as chiral auxiliary, which may form a seven-membered chelate with a Lewis acid in the allylation by allylmetal compounds.1. We synthesized some, camphor-derived sulfides and sulfoxides and selected the enantioselective addition of bezaldehyde with diethylzinc. When benzaldhyde was reacted with diethylzinc using beta-oxysulfides, (S) -1-phenyl -1-propanol was obtained in up to 82%e.e.under the optimized conditions.2.We undertook the asymmetric addition of an allylmetal compound to chiral beta-sulfinyl aldehyde in the presence of a Lewis acid. Despite of numerous reports for asymmetric condensations using alpha-sulfinyl carbonyl compounds, little work has been done on the asymmetric addition to beta-sulfinyl carbonyl compounds because of its low performance in chelation control. We thus synthesized chiral beta-sulfinyl carbonyl compounds i.e., chiral p-tolylsulfinyl fyrylaldehydes and examined the diastereoselective addition reactions. The addition of allyltriphenylstannane to 3-sulfinylfurfural in the presence of titanium (IV) tetrachloride proceeded with high diastereoselectivity to give the homoallyl alcohol. On the other hand the similar treatment of the sufinyl aldehyde with tin (IV) tetrachloride afforded the other diastereoisomeric alcohol, exclusively.The similar results were also obtained in the case of chiral, sulfinyl-substituted thienyl aldehyde.