Stereoselective reductions and alcohol deoxygenation by a phosphine in the 5,10-dihydrodibenzo[b,e]phosphorin series

Abstract

The stereospecific reductions of the 5-methyldibenzo[b,e]phosphorin-10(5H)-one (4) by NaH₂Al(OC₂H₄OMe)₂ and LiHAl(OBu^t)₃ give the pseudoaxial and pseudoequatorial alcohols (14) and (13), respectively. Alcohol (13), but not (14), undergoes ready oxygen transfer from carbon to phosphorus. LiAlH₄ deoxygenates the pseudo-equatorial alcohol 5-methyl-5,10-dihydrodibenzo[b,e]phosphorin-10-ol 5-oxide (6), but not the corresponding pseudoaxial alcohol (7), to the phosphine oxide (8). Neither the isomeric alcohols (6) and (7) nor their acetate esters (17) and (18) equilibrate or isomerize under electron impact at 200 °C.