Hitosi Nozaki

Novel distannoxane-catalyzed transesterification and a new entry to α, β-unsaturated carboxylic acids

Abstract Novel distannoxane-catalyzed transesterification reaction has been developed which affords various types of esters under very mild conditions. The reaction was applied to the stereo- and regioselective synthesis of trisubstituted α,β-unsaturated carboxylic acids.

Organotin triflate as practical catalyst for Michael addition of enol silyl ethers

Abstract Dityltin bis(triflate) is a mild Lewis acid which catalyzes clean Michael addition of enol silyl ethers. The new catalyst allows to employ various labile acceptors such as methyl vinyl ketone and 2-cyclopentenone which do not undergo smooth reaction with conventional Lewis acids. A variety of enol silyl ethers are also employable and thus 2-(trimethylsiloxy)propene, the simplest one in this class of compounds, can be used. The adducts of enol silyl ethers of cycloalkanones with vinyl ketones are readily cyclized to give the desired annulated enones free from isomers. Consequently, a practical version of the Robinson annulation has been realized.

Distannoxane-catalyzed cleavage of acetals and silyl ethers

Abstract Deprotection of acetals including tetrahydropyranyl ethers and of silyl ethers can be achieved under neutral conditions by use of a distannoxane catalyst in excellent yields.

A novel template effect of distannoxane in macrolactonization of ω-hydroxy carboxylic acids

Abstract A novel template effect of 1,3-disubstituted tetrabutyldistannoxanes in macrolactonization of ω-hydroxy carboxylic acids has been disclosed.

Methoxy(phenylthio)methane as an ambi-equivalent of a methoxy- or phenylthiomethylene 1,1-dipole

Abstract Methoxy(phenylthio)methane undergoes electrophilic alkylation followed by nucleophilic allylation or propargylation which is dramatically changed depending on the Lewis acid employed providing a methoxy- or phenylthiomethylene 1,1-dipole synthon.

Activation and synthetic applications of thiostannanes. Conversion of aldehydes and acetals into 1,3-dithianes with high chemodifferentiation

Abstract Novel method for transforming aldehydes and acetals into 1,3-dithianes has been achieved with the aid of organotin thioalkoxides and organotin triflates. Under these reaction conditions, various acid-sensitive groups are tolerated. Differentiation between aromatic or aliphatic aldehydes and acetals has been realized.

Activation of ketene silyl acetals by 10-methylacridinium perchlorate: a novel catalysis in mukaiyama reaction

Abstract 10-Methylacridinium perchlorate ( 1 ) effectively promotes various reactions of ketene silyl acetals: aldol and Michael addition products are obtained with aldehydes, ketones, acetals, and α-enones. The reactions exhibit unusual dependency upon 1 , namely the yields are excellent when a catalytic amount of 1 is employed whereas no desired products are accessible by the use of 1 in a stoichiometric quantity. A novel catalytic cycle is proposed.

Unique template effects of distannoxane catalysts in transesterification of diol esters

Abstract 1, n -Diol diacetates (n = 2,3,4) are selectively converted into the corresponding monoacetates by distannoxane-catalyzed transesterification. Such unique selectivity is not encountered with 1, n -diol diacetates where n ≥ 5. A great difference in reactivity is also seen in the transesterification between methyl butyrate and 1, n -diol monoacetates: the ethylene glycol derivative sluggishly undergoes transesterification whereas higher homologs react smoothly. The unique template effects of the catalysts are discussed in terms of cooperation of to different tin atoms which are located in the proximity.

Activation and synthetic applications of thiostannanes. A new method for synthesis of thio- and selenoglycosides

Abstract Exposure of thiostannane to acetyl or methyl glycosides in the presence of a catalytic amount of Bu 2 Sn(OTf) 2 provides thioglycosides in good yields. Selenoglycosidation is achieved in a like manner by use of selenostannane.

Activation and synthetic applications of thiostannanes: Thioalkoxylation of acetals

Abstract The Sn-S bonds in thiostannanes, Bu n Sn(SPh) 4−n , are activated towards acetals in the presence of BF 3 · OEt 2 . Acetals of various aldehydes and ketones are converted into the corresponding monothioacetals under mild conditions. Employment of α -enal acetals induces Michael addition to give synthetically useful γ-alkoxyally sulfides.