Masao Hirayama

Asymmetric synthesis of (+)-phosphinothricin and (+)-2-amino-4-phosphonobutyric acid

Abstract Asymmetric synthesis of (+)-phosphinothricin, (+)-2-amino-4-phosphono-butyric acid, and their enantiomers has been achieved by the Michael addition of chiral glycine Schiff bases to vinyl phosphorus compounds.

Stereocontrolled synthesis of withanolide D and related compounds

The synthesis of withanolide D, a withanolide having a hydroxy group at the C-20 position, has been accomplished from pregnenolone. The key reactions are based on successful stereochemical control at the C-22 position involving γ-coupling reaction of a lithium enolate with a protected 20-hydroxy-22-aldehyde, and allyl sulphoxide–sulphenate rearrangement of 2,4-dien-1 -one 6β-sulphoxide to introduce the 4β-hydroxy-2,5-dien-1-one system. The related natural withanolides, physalolactone B, deacetyl-physalolactone B, and 3α,20R-dihydroxy-1-oxowitha-5,24-dienolide were also synthesized via a common intermediate for withanolide D.

Stereoselective synthesis of withafein A and 27-deoxywithaferin A1

Abstract The first stereoselective synthesis of withaferin A and 27-deoxywithaferin A was described. The key steps in the synthesis involve introduction of the desired substituent at C 25 and steroselective construction of the A:B rings by a facile allyl sulfoxide—sulfenate rearrangement.

Synthetic studies of withanolides. Part 2. Synthesis of 4aβ,5β-epoxy-4a,5,6,7,8,8a-hexahydro-4β-hydroxy-8aβ-methylnaphthalen-1(4H)-one and related compounds

The title compound, a simple AB ring moiety of withaferin A, and its seven isomers, were synthesized via octahydro-4a-hydroxy-5-(phenylthio)-8a-methylnaphthalen-1(2H)-ones [(5a) and (5b)]. The key steps in the synthesis involve either 1,2-phenylthio-migration, or dehydration reactions of (5a) and (5b).

Oxidation of ethyl trans- and cis-3-bromo-1-methyl-2-oxocyclohexanecarboxylates by dimethyl sulphoxide

Ethyl c-3-bromo-1-methyl-2-oxocyclohexane-r-1-carboxylate (1a) is oxidized by dimethyl sulphoxide to the 2,3-dione derivative (3), whereas the t-3-bromo-isomer (1b) is apparently dehydrogenated to give the bromocyclohexenone (4). The mechanism for the formation of the product (4) is discussed. Allied reactions are described.