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1999 stereochemistry
stereochemistry (general, optical resolution)O 0030
45 - 0491,3-Stereocontrol with Phosphine Oxides: Asymmetric Synthesis ofall Four Diastereoisomers of a γ’-Benzyloxy β-Hydroxy PhosphineOxide. — Several optically active phosphine oxides exhibit moderatelevels of 1,3-asymmetric induction by lithiation and subsequent reaction withaldehydes or esters to give the title compounds. Complementary routes to allfour diastereomeric alcohols (III), (IV), (VI), and (IX) are developed startingfrom the same phosphine oxide (I). The anti phosphine oxides (III) or (IV)are synthesized by addition of aldehyde (II) to the lithiated phosphine oxide.Depending on the solvent, THF or toluene, diastereomers (III) or (IV) areformed predominantly. Alternatively, β-keto phosphine oxides, generated eitherby oxidation of the alcohol (III) with Dess–Martin periodinane or by acylationof phosphine oxide (I) with ester (VII), are reduced with NaBH4 to give the synisomers (VI) or (IX) with high selectivity. The success of the complementaryroutes hinges on the configurational instability of the lithiated phosphineoxides. The access to anti and syn diastereomeric series is possible becausealdehydes and esters react preferentially with different isomers of a rapidlyequilibrating mixture of lithiated phosphine oxides. The β-hydroxy phosphineoxides are shown to be valuable intermediates in the synthesis of opticallyactive homoallylic alcohol derivatives like (V) and (XI). — (NELSON, ADAM;WARREN, STUART; J. Chem. Soc., Perkin Trans. 1 (1999) 14, 1963-1982;Sch. Chem., Univ. Leeds, Leeds LS2 9JT, UK; EN)
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