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, important 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 adducts 6. Subsequent ozonolysis afforded alpha-phosphanyl ketones 7, The enantioselective synthesis of 2-phosphanyl alcohols 12 and 13 has been accomplished by two fundamentally different procedures: the phosphanylation of unsubstituted chiral aldehyde hydrazones 9 and the alkylation of alpha-diphenylphosphanyl acetaldehyde SAMP hydrazone 10. After separation of the minor diastereomer, the borane-protected alpha-phosphanyl aldehyde hydrazones 11 were converted to unprotected 2-phosphanyl alcohols 13 by ozonolysis, reduction and removal of the borane group. The absolute configuration of the functionalized phosphanes was determined by X-ray analysis, NOE experiments or polarimetry.