Enolate Additions to a Chiral 3-Hydroxypropionate 2,3-Dication Equivalent. Enantioselective Synthesis of beta,delta-Dihydroxy Esters.
The use of optically active dicarbonyl cyclopentadienyliron(vinyl ether) BF(4) 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 (eta-cyclopentadienyliron)(eta(2)-1-methoxypropene) BF(4) 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.
Zhen
W.
W
Department of Chemistry, Brandeis University, Waltham, Massachusetts 02254.
Chu
K.-H.
KH
Rosenblum
M.
M