FACILE SYNTHESIS OF 1,2,3,4,5,6-HEXAHYDROPHOSPHININE 1-OXIDES BY THE HYDROGENATION OF 1,2-DIHYDROPHOSPHININE 1-OXIDES

Abstract

The hydrogenation of the dihydrophosphinine oxides obtained from 3-methyl- or 3,5-dimethyl-1-alkoxy-2,5-dihydro-1H-phosphole oxides on ring enlargement gives the diastereoisomers of new hexahydro-phosphinine oxides. Conformational analysis of the 3-methyl-products suggests the equilibria to be strongly biased toward structures with an equatorial C-methyl substituent. In contrast, the predominant diastereoisomer of the 3,5-dimethyl-product exists as an equilibrium of two conformers. A new P-chloro-hexahydrdophosphinine has also been prepared from the ethoxy-derivative which is useful in the synthesis of the amino-product. The hexahydrophosphinine oxides are characterized by ³¹P, ¹³C and ¹H NMR and mass spectroscopic methods.

Key Words:

• Dihydrophosphinine oxide
• hydrogenation
• hexahydrophosphinine oxide
• diastereoisomer
• conformer
• stereospecific coupling