Enolate Additions to a Chiral 3-Hydroxypropionate 2,3-Dication Equivalent. Enantioselective Synthesis of β,δ-Dihydroxy Esters

Article abstract of DOI:10.1021/jo9621940

The use of optically active dicarbonyl cyclopentadienyliron(vinyl ether) BF4 salts, 3 and 4, as enantioselective 3-hydroxypropionate 2,3-dication equivalents is outlined.Complexes 3 and 4 are readily available by exchange etherification of 2, and these have been transformed to enantiomeric dicarbonyl (η-cyclopentadienyliron)(η²-1-methoxypropene) BF4 5 and ent-5.Complex 5 has been converted to the corresponding p-methoxybenzyloxy vinyl ether complex 7 by exchange etherification.Condensation of this salt with a number of terminal and nonterminal enolates yields adducts, which are then transformed by redox-promoted alkoxycarbonylation, followed by alcohol deprotection, to optically active 2-methyl-3-hydroxy-5-keto esters. 1,3-Reduction of these ketols can be effected to give either syn- or anti-1,3-diols and thence their related pentanolides.