Masayuki Shimagaki

Highly stereoselective reduction of α-methylthio and α-phenylthio ketones synthesis of syn- and anti-β-methylthio- and β-phenylthioalcohols

Abstract Reduction of α-methylthio and α-phenylthio ketones 1 with L-Selectride gave syn-alcohols 2 in high stereoselectivity except when R1 was cyclohexyl group, while reduction with Zn(BH4)2 gave the isomeric anti-alcohols 3 provided R3 was methyl group.

Highly stereoselective reduction of β-oxosulfonium salts ---synthesis of trans epoxides---

Abstract Alkylation of α-methylthio or α-phenylthio ketones 1 with trimethyloxonium tetrafluoroborate and the reduction of the resulting sulfonium salts 5 with naBH 4 followed by the base treatment afforded trans-epoxides 8 with high stereoselectivity.

Highly stereoselective reaction ofα-methylthio aldehydes with allyltriphenylstannane: Synthesis of anti-β-methylthio alcohols

Abstract The reaction ofα-methylthio aldehydes 4 (R=1°, 2°) with allyltriphenylstannane 5 in the presence of SnCl 4 gave anti-β-methylthio alcohols 6 in excellent selectivity.

Synthesis of acyclic polyol derivatives via enzyme-mediated aldol reaction

Abstract Enzyme-mediated stereoselective aldol reaction between dihydroxyacetone phosphate (DHAP, 1 ) and (2 R ,4 R )-6-benzyloxy-2,4-dimethoxyhexanal ( 8 ) was catalyzed by rabbit muscle aldolase (RAMA) to generate (3 S ,4 R ,5 R ,7 R )-trihydroxyketone 12 , which could be easily transformed to the masked polyhydroxylated compound 15 corresponding to the C-9∼C-16 segment of pentamycin ( 6 ).

A stereoselective synthesis of Z)-α,β-disubstituted acrylates

A new route for (Z)-α,β-disubstituted acrylate is described which is made up of 1) stereoselective reduction of ketones 3 and 2) conversion of the resulting syn-2 into (Z)-1.

NEW SYNTHETIC METHODS FOR OLEFINS FROM SECONDARY PHOSPHATES AND THIOPHOSPHATES

Abstract The reaction of phosphates 1 and 5 and thiophosphates 3 and 7 gave the olefins 2 and 6 with 0.8 – 1.6 mol eq of Lawessons reagent in xylene at reflux. Compounds 1, 3, 8, 5 and 7 gave 2 and 6 in better yields with a small amount of AgOTf (0.1 – 0.3 mol eq) even in toluene at reflux.

2-HALOVINYL ARYL SULFONES: NEW COUPLING REAGENTS FOR CARBOXAMIDE FORMATION1

Abstract E-2-Chlorovinyl p-nitrophenyl sulfone 6 and 2-bromo-2-trifluoromethylvinyl phenyl sulfone 7a reacted with carboxylic acids in the presence of a molar equiv of Et3N affording the corresponding 2-acyloxyvinyl sulfones 8, 11, 17, 18, 22, 25, 28 and 29. The latter, on treatment with amines, gave amides 9, 13, 19, 23 and 26 and peptides 30 and 32. These reagents 6 and 7a were also used for the formation of N-methylanilides 13d, 13e, 19d, 23 and 26. Particularly, 6 was successfully used for synthesis of a macrocyclic lactam 23 involving a N-methylanilide moiety. The amidation reactions proceeded under essentially neutral conditions. Therefore, base-sensitive β-hydroxycarboxy-N-methylanilides such as 26, whose structural unit was involved in maytansine 5, could be prepared by the present method. The reagent 6 was also effective for the preparation of peptides such as Val-N-MeVal derivatives (e.g. 32), which were difficult to prepare by other methods.