pyridine-catalyzed reaction between a number of propanedioic acid derivatives 1 and thionylchloride has been investigated in detail. Contrary to popular belief the straightforward formation of the corresponding α-chloro sulfenyl chlorides 2 is the exception rather than the rule. The propanediamide 2e, not available by the “standard” reaction of 1e with thionylchloride, is surprisingly formed by reaction of 1e
Regioselective Enzyme-Mediated Acylation of Polyhydroxy Natural Compounds. A Remarkable, Highly Efficient Preparation of 6'-Acetyl and 6'-O-Carboxyacetyl Ginsenoside Rg1
Lipase B from Candida antarctica has been shown to be an efficient catalyst for the regioselective acylation of the dammarane type glucoside ginsenoside Rg(1) (1) on reaction with vinyl acetate in t-AmOH, affording the corresponding 6'-O-acetyl derivative 1b in high yield. The structure of 1b was determined through a careful inspection of its H-1 NMR at 600 MHz, which allowed for the complete assignment of the signals of the sugar's protons. The introduction of a carboxyacetyl residue was then investigated using different protocols. The best results were obtained with a two-step sequence involving the preliminary enzymatic acylation of 1 with bis(2,2,2-trichloroethyl) malonate to give the mixed malonyl derivative 1f, followed by selective chemical hydrolysis with Zn/AcOH to the 6'-O-carboxyacetyl ginsenoside Rg(1) (1e).
GARST, MICHAEL E.;MCBRIDE, BILL J., J. ORG. CHEM., 54,(1989) N, C. 249-250
作者:GARST, MICHAEL E.、MCBRIDE, BILL J.
DOI:——
日期:——
SYNTHESIS OF METHYLENE MALONATES USING RAPID RECOVERY IN THE PRESENCE OF A HEAT TRANSFER AGENT