SYNTHESIS AND STEREOCHEMISTRY OF 1-OXA-6-HETERASPIRO[2.5]OCTANES. SINGLE-CRYSTAL ANALYSIS OF 6-PHENYL-1-OXA-6-PHOSPHASPIRO[2.5]OCTANE 6-SULFIDE

Abstract

The synthesis of several 1-oxa-6-heteraspiro[2.5]octanes is reported herein for the first time. Stereochemical analysis via NMR studies and a single crystal X-ray diffraction analysis of 6-phenyl-1-oxa-6-phosphaspiro[2.5]octane 6-sulfide have been completed and provide the basis for correlations of structures for other members of the families yet unknown. Epoxidation of cis-2,6-diphenyl-4-thianone with dimethyl-oxosulfonium methylide in DMSO led, surprisingly, to a tertiary alcohol, presumably via ring opening of the expected intermediate epoxide. This is the first example of this type of ring opening in the presence of this base but the reaction time was longer than that normally employed in this process.

Since the family members of the parent spiro[2.5]octanes are rare, an X-ray diffraction analysis was performed on 6-phenyl-1-oxa-6-phosphaspiro[2.5]octane 6-sulfide. This analysis revealed a space group of Pna2₁ with cell dimensions of: a=13.056(3) A, b=14.268(3) Å, and c=6.1522(11) Å. The phosphorinane ring assumes a slightly flattened chair conformation with the phenyl-P bond being equatorial and the P[dbnd]S bond being axial. The plane of the epoxide is virtually coincident with a pseudo-mirror plane through P(6), C(3), C(9) and S(15). The phenyl group is rotated out of this plane by 28.2°. Although the P—C distances (ring carbons) are 1.813(3) Å and 1.819(3) Å, respectively, and appear to be about normal, the P-phenyl bond of 1.813(3) Å is longer than in a few model systems. The C(3)—O(1) bond in the epoxide is axial or rather pseudo axial. Ring deformations are consistent with a few model epoxides the structures of which have been identified.