Akio Takuwa

Divergently stereocontrolled reaction of an allylic silane bearing an asymmetric ethereal carbon toward aldehydes

Lewis acid mediated allylation of aldehydes by an allylsilane bearing an asymmetric ethereal functionality proceeded in divergently stereocontrolled manners, i.e., TiCl4 afforded the syn isomer, whereas BF3·OEt2 afforded the anti isomer predominantly.

Optically active allylic tin reagent as an enantio-divergent synthon of isoprenoids via remote and divergent asymmetric induction

Abstract ( S )-2-(1-Hydroxymethyl)allytin ( 1a ) can be prepared in high enantiomeric purity. When its methylated and acetylated derivatives are allowed to add to aldehydes with the help of i -PrOTiCl 3 and SnCl 4 , syn- and anti- homoallylic alcohols are stereoselectively obtained, respectively, via 1,4-asymmetric induction. These reactions are applied to the synthesis of the both enantiomers of a pheromone constituent, ipsenol, from a single enantiomer of 1a .

α-Regioselective and stereospecific addition of allylic tins to aldehydes via photoinduced electron transfer

Abstract (E)- and (Z)-Allylic tributyltins add to aromatic aldehydes to afford regioreversed α-adduct predominantly with almost complete retention of the stereochemistry of the allylic groups under photochemical conditions. The photoinduced single electron transfer mechanism is proposed.

Substituent-control of stereoselectivity in the reaction of allylic tins. Anti-selective lewis acid-promoted reaction toward aldehydes

Abstract In the reaction of cis -2-alkenyltins (allylic tins) toward aldehydes, unusual anti -homoallyl alcohols were selectively obtained when the substituent at the 2-position of the alkenyltin reagent was a bulky one such as a tert -butyl or trialkylsilyl group. This reaction is assumed to proceed via the inverse antiperiplanar acyclic transition state.

Reversible stereocontrol in the Lewis acid promoted reaction of alkoxyaldehydes toward various allyltins

Abstract In the reactions of variously substituted allyltin reagents toward achiral alkoxyaldehydes, one of the diastereomeric homoallyl alcohols was stereoselectively obtained by the help of BF 3 , while TiCl 4 preferentially gave the other diastereomer, though ( E )- and ( Z )-3-monoalkylallyltin reagents were exceptional. This reversible diastereoselectivity can be explained by the coordination geometry ( anti or syn ) of the Lewis acids toward alkoxyaldehydes.

Stereospecificity in the Lewis acid promoted allylation reaction of 3,3-disubstituted allyltins toward aldehydes

Abstract The Lewis acid-promoted reaction of 3,3-disubstituted allyltins toward aldehydes was found to be stereospecific; the ( E )-reagent gave syn -products and the ( Z )-one gave anti -products. This is in contrast to that of 3-mono-substituted congeners which are known to react syn -stereoselectively regardless of their double bond geometry. The reaction was assumed to proceed via an acyclic syn -synclinal transition state.

PHOTOCHEMICAL 1,3-STANNYL MIGRATION OF 3-ARYL-SUBSTITUTED ALLYLTINS

Abstract Intramolecular [1,3]-stannyl migration of (3-aryl-2-propenyl)trialkyltins took place reversibly in chloroform, or in the presence of an alkyl halide or a radical scavenger in benzene under irradiation with >320 nm light.

Stereospecific formation of deuterated homoallyl alcohols by Lewis acid-promoted reactions of allyltin and allylsilicon reagents toward aldehydes

Abstract Stereoselectively prepared ( Z )-3-deuterioallyltin and ( E )-3-deuterioallylsilicon were allowed to react with aldehydes in the presence of BF 3 ·OEt 2 . The stereospecifically afforded products were predominantly an anti -homoallyl alcohol from the ( Z )-reagent and a syn -one from the ( E )-reagent. These results strongly indicate both reactions proceed via a syn -synclinal transition state.

Unsual ε/γ-regiospecificity of (E/Z)-pentadienyltin in the Lewis acid-promoted reaction with an aldehyde

In the Lewis acid-promoted reaction between pentadienyltin (PDT) and an aldehyde, (E)-and (Z)-PDTs exhibit opposite regioreactivities: (E)-PDT reacts at the terminal Iµ-position and (Z)-PDT at the internal γ-position.

Structural influences on the isomerization of 4-benzyl- and 4-allyl-1,2-naphthoquinones to quinonemethides and their stereochemistry

The isomerization of 4-benzyl-1,2-naphthoquinones and 4-allyl-1,2-naphthoquinones to quinonemethides has been studied. The steric interaction and extra π conjugation in the quinonemethide, and acidity of methylene protons of the quinone, are controlling factors for the isomerization. 1H N.m.r. studies suggested that the quinonemethides have the E configuration.