3-Halopropenyl esters as precursors of a new class of oxygen-substituted allylic organometallic compounds:Applications in organic synthesis

摘要

3-Halopropenyl esters,readily prepared by the addition of acyl halides to acrolein,react with zinc,indium,and chromium(II),thus opening a route to a new class of oxygen-substituted allylic organometallic compounds.Indium and zinc reagents smoothly add to car-bonyl compounds,affording alk-l-en-3,4-diol derivatives in a variety of synthetic procedures which include typical Grignard stepwise conditions as well as Barbier one-pot protocols.Using zinc and indium in water or aprotic solvents,simple diastereoselectivity was found to depend on the nature of the carbonyl compound;conjugated aldehydes favor formation of syn-adducts while unconjugated aldehydes favor anti-adducts.Moving to chromium,a reversal of regioselectivity was observed in favor of (Z)-4-hydroxy-enolacetates,flexible protected forms of homoaldols.Chromium complexes are generated in a catalytic cycle based on the combined use of the redox Mn(0)/Cr(III) couple and of TMSC1.When the Cr-cat-alyzed reaction is carried out in the presence of Jacobsen's Salen ligand,the regiochemical outcome of the reaction is again reversed,and syn-alk-l-en-3,4-diols are formed in high ee's.