Reactions of the Bornyl and Fenchyl Grignard Reagent with Chlorophosphanes – Diastereoselectivity and Mechanistic Implications

The reactions of the bornyl and fenchyl Grignard reagent with the chlorophosphanes Ph 2 PCl, PCl 3 and (Et 2 N) 2 PCl, respectively, were studied by multinuclear NMR spectroscopy. The diastereoselectivity was found to be independent of the diastereomeric composition of the bornyl andfenchyl Grignard reagent (e.g., the endo / exo ratio), but dependent on the chlorophosphanes used. The results are consistent with a reaction mechanism that involves SET processes and radical intermediates. No or little diastereoselectivity was observed for the reactions involving Ph 2 PCl and PCl 3 . The reactions of the bornyl and fenchyl Grignard reagent with (Et 2 N) 2 PCl provided bornylP(NEt 2 ) 2 ( 4a ) and β‐fenchylP(NEt 2 ) 2 ( 10b ) with high diastereoselectivity (of 92 % and 88 % de ). The novel chiral phosphane oxides bornylPh 2 PO ( 2a ), isobornylPh 2 PO ( 2b ), α‐fenchylPh 2 PO ( 8a ) and β‐fenchylPh 2 PO ( 8b ), phosphinic acids bornylP(O)(H)(OH) ( 5a ) and β‐fenchylP(O)(H)(OH) ( 11b ) and phosphonic acids bornylP(O)(OH) 2 ( 6a ) and β‐fenchylP(O)(OH) 2 ( 12b ) were isolated as colorless crystals. The molecular structures of 2b , 8a , 8b , 6a and 12b were determined by X‐ray crystallography.