Yukiyasu Chounan

Unprecedented rearrangement reaction of 2-aziridinemethanols with lower order lithium methylcyanocuprate

Abstract Complementary selectivity can be achieved in ring opening reactions of 2-aziridinemethanols by using either the Gilman reagent or lower order cyanocuprate. In the former case, the usual attack of the Gilman reagent to the substrates 1 and 2 results in the formation of the expected ring opening products ( 3 and 4 ) and ( 7 and 8 ), respectively. In contrast, exposure of both 1 and 2 to the lower order cyanocuprate proceeds in an unprecedented fashion, presumably via epoxides D and G , to yield unexpected secondary alcohols ( 11 and 12 ) as the major products.

Allylation of ketones with allylstannanes catalyzed by Lewis acid–Lewis base combined reagents

Abstract Although the Lewis acid promoted allylation of ketones with allylstannanes gives the corresponding tert -homoallyl alcohols in lower yields in comparison with those of aldehydes, the use of Lewis acid–Lewis base combined catalysts such as Zn(OTf) 2 –2,6-lutidine and Zn(OTf) 2 –pyridine dramatically enhances the yield of the tert -alcohols.

SN2′ selective alkylation of allylic chlorides and mesylates with RZnX reagents generated from Grignard reagents, zinc chloride, lithium chloride, and Cu(II)-salts

Abstract Treatment of RMgX (1 equiv. R = alkyl; X = Cl, Br) with ZnCl 2 (1 equiv.) in a mixed solvent of THF and Et 2 O leads to a highly turbid white suspension. Addition of LiCl (1∼2 equiv.) solubilizes the insoluble species to yield a colorless clear solution. Addition of a catalytic amount of a Cu(II)-salt followed by allylic halides or mesylates at 0 °C ∼ room temperature yielded S N 2′products in high yields. Application for the synthesis of ( E )-alkene dipeptide isosteres is also reported.

1,2-Asymmetric Induction in the Conjugate Addition of Organocopper Reagents to γ-Aryl α,β-Unsaturated Carbonyl Derivatives

Abstract The diastereoselectivity in the conjugate addition of organocopper reagents to γ-aryl α,β-unsaturated carbonyl derivatives 8–14 was investigated. The syn -diastereoselectivity was obtained irrespective of the reagents type in the addition of 8, while the anti -diastereoselectivity was obtained in the addition of 10–14 with RCu and RCu(CN)Li (R=Me and Bu) and the syn -selectivity was produced in the addition of 10–14 with R 2 CuLi and R 2 Cu(CN)Li 2 . The reagent controlled and substrate dependent diastereoselectivity are explained by two different reaction pathways: either π-complex formation or ordinary nucleophilic addition. Reduction potentials of the Michael acceptors and electron donating ability of organocopper reagents control the reaction pathway.

“Higher order” zinc cuprates involving lithium chloride: Synthesis of (E)-alkene dipeptide isosteres free from reductive elimination products

Abstract The “higher order” organozinc cuprates, R 2 Cu(CN)(ZnCl) 2 ·2Mg(X)Cl·nLiCl, derived from admixture of LiCl (1∼2 equiv.), ZnCl 2 (1 equiv.), RMgX (1 equiv.), and CuCN (0.5 equiv.) in a mixed solvent of THF and Et 2 O exhibit high diastereoselection of up to > 99: 1 in the synthesis of (E)-alkene dipeptide isosteres from γ-mesyloxy-α,β-unsaturated esters. Addition of lithium chloride is essential for the preparation of clear solutions of reagents.

PALLADIUM-CATALYZED BENZANNULATION OF CONJUGATED ENYNES. ENHANCED REACTIVITY OF ALKOXYCARBONYL- AND CYANOENYNES

Abstract We report the high reactivity of alkoxycarbonyl- and cyanoenynes in the homo-benzannulation of conjugated enynes. The introduction of these electron-withdrawing groups enabled us to carry out the benzannulation of 1-substituted enynes as well as 1,2- and 2,4-disubstituted enynes, which have much lower reactivity compared to 2- or 4-monosubstituted enynes. Polysubstituted benzenes were prepared in a highly regioselective manner in good to excellent yields.

Remarkable difference in reactivity of ordinary vinylcopper reagents and vinylzinc halide containing a copper salt towards γ-mesyloxy-α, β-enoates. Synthesis of homochiral 1,4-dienes

Abstract Whereas the reaction of γ-mesyloxy α,β-enoates with vinyl-Cu(CN)M or (vinyl) 2 Cu(CN)M 2 (M = Li or MgX) yielded a reduction product with an ( E )-double bond at the β,γ-position, treatment of the same substrates with “higher order” zinc cuprate reagents or vinyl-ZnCl by the addition of a catalytic amount of Cu(I) or Cu(II) salt afforded α- and γ-vinylation products. Both vinylation products were stable 1,4-diene derivatives that are only more difficulty accessed by more traditional means.

A chemical scale for electron-transfer ability of methylcopper reagents

The ratio of methyl transfer (2) and reduction (3) products in the reaction of trimethoxycarbonylethylene 1 with methylcopper reagents MeCuLn varies with the copper species, and decreased in the following order: MeCu(CN)Li > MeCu > Me2Cu(CN)Li2≫ Me2CuLi > Me3CuLi2.