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

1997-05-16T00:00:00Z (GMT) by W. Zhen K.-H. Chu M. Rosenblum
The use of optically active dicarbonyl cyclopentadienyliron(vinyl ether) BF<sub>4</sub> salts, <b>3</b> and <b>4</b>, as enantioselective 3-hydroxypropionate 2,3-dication equivalents is outlined. Complexes <b>3</b> and <b>4</b> are readily available by exchange etherification of <b>2</b>, and these have been transformed to enantiomeric dicarbonyl (η-cyclopentadienyliron)(η<sup>2</sup>-1-methoxypropene) BF<sub>4</sub> <b>5</b> and <i>ent</i>-<b>5</b>. Complex <b>5</b> has been converted to the corresponding <i>p</i>-methoxybenzyloxy vinyl ether complex <b>7</b> 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 <i>syn</i>- or <i>anti</i>-1,3-diols and thence their related pentanolides.