Conformational Studies of a Six-Membered Phostone

Abstract

Abstract Although 1,3,2-dioxaphosphorinanes generally assume chair conformations,1 there are examples in which the ring adopts the boat or twist-boat form.1 Recent studies on the synthesis, stereochemistry, and reactivity of 2-alkoxy-2-oxo-1,2-oxaphosphorinanes (phostones) have revealed both cis and trans isomers of 3-(diphenylhydroxymethyl)-2-ethoxy-2-oxo-1,2-axaphosphorinane2 to assume a chair conformation in the solid state. In the present work, the conformational properties of cis and trans-3-methoxycarbonyl-2-methoxy-2-oxo-1,2-oxaphosphorinanes were investigated by X-ray analysis, variable temperature 31P, 1H and 1H{31P} NMR spectroscopy, molecular mechanics, and semiempirical calculations. The X-ray crystal structure of the trans isomer revealed a chair dormation with equatorial phosphoryl and carbomethoxy groups. No changes were observed in the 31P NMR spectra of either isomer in the temperature range of 183–333 K. A complete set of vicinal JHH coupling constants was extracted from the 1H{31P} spec...