HIGH- AND ATMOSPHERIC-PRESSURE CYCLOADDITION OF TRICHLOROACETYL ISOCYANATE TO 3,4-DI-O-ACETYL-L-RHAMNAL

Article abstract of DOI:10.1016/S0040-4020(01)86897-6

High- and atmospheric-pressure cycloaddition of trichloroacetyl isocyanate (2) to 3,4-di-O-acetyl-L-rhamnal (11) leads to formation of four products: α-gluco (4+2)cycloadduct 12, two stereoisomeric α-gluco 13 and β-manno 14 (2+2)cycloadducts, and α,β-unsaturated amide 15.The isocyanate enters the rhamnal molecule preferentially anti with respect to the 3-O-acetyl substituent.It is found that under conditions of both-high and normal pressure (4+2)cycloaddition is preferred(2+2)cycloaddition, more so under high pressure.Under normal pressure, better stereoselectivity in (2+2)cycloaddition is obtained.Elevation of temperature and prolongation of the reaction time promote rearrangement to α,β-unsaturated amide. Transformations of the reaction products into N-unsubstituted: 1-O-trichloroacetyl compound 20, methyl glycosides 23 and 24, β-lactam 25, α,β-unsaturated amide 26, and into the 4-aza-2,10-dioxabicyclo(4.2.0)decan-5-one skeleton 16-19 are described.