EVIDENCE FOR SELECTIVE S-ALKYLATION OF AN AMBIDENT ANION OF DICYCLOHEXYLAMMONIUM THIOPHOSPHONATE BY ALKYL HALIDES

Abstract

Reaction of the DCHA salt of O-alkyl phenyl phosphonothioic acids 1a–c with alkyl halides 2a-d gave exclusively S-derivatives; 3e–h (85–93%) and 3b-d (40–43%). The cause for poor yields of the methyl analogues is its ability to participate in the methylation of salt 1a and give rise by-product O,S-dimethyl phenyl phosphonothiolate (3a). Awareness of the unusual pathway for the generation of the by-product has opened a new possibility to adopt this strategy for synthesis of enantiomerically pure thiolates.

Key Words:

• Chiral phosphonothiolates
• dicylohexylammonium thiophosphonate anion
• resolution
• stereospecific synthesis
• cross methylation
• alkyl halides.