ENANTIOSELECTIVE SYNTHESIS OF ALPHA-PHOSPHANYL KETONES AND 2-PHOSPHANYL ALCOHOLS

An efficient, highly enantioselective methodology for the synthesis of alpha-phosphanyl ketones 7 and 2-phosphanyl alcohols 12 and 13, impor tant hemilable ligands for enantioselective homogeneous catalysis and chiral building blocks in general, has been developed. The key step of this first enantioselective synthesis of alpha-phosphanyl ketones is the diastereoselective phosphanylation of SAMP hydrazones 2 to produce alpha-phosphanyl hydrazones, isolated as the more stable borane adduc ts 6. Subsequent ozonolysis afforded alpha-phosphanyl ketones 7, The e nantioselective synthesis of 2-phosphanyl alcohols 12 and 13 has been accomplished by two fundamentally different procedures: the phosphanyl ation of unsubstituted chiral aldehyde hydrazones 9 and the alkylation of alpha-diphenylphosphanyl acetaldehyde SAMP hydrazone 10. After sep aration of the minor diastereomer, the borane-protected alpha-phosphan yl aldehyde hydrazones 11 were converted to unprotected 2-phosphanyl a lcohols 13 by ozonolysis, reduction and removal of the borane group. T he absolute configuration of the functionalized phosphanes was determi ned by X-ray analysis, NOE experiments or polarimetry.