1.3- Dioxin vinylogous esters

Dioxin vinylogous esters derived from cyclic 1,3-diketones (e.g., 4) are valuable building blocks for the construction of natural and unnatural carbocyclic products.2 In connection with a synthesis of plant-growth regulators, Crow and... 

The synthetic usefulness of dioxin vinylogous esters as p-keto vinyl cation equivalents was demonstrated by a variety of reductive and alkylative 1,3-carbonyl transpositions.5 7 Regioselective alkylation and hydroxylation at the a -position (and, in some cases, at the y-position)8 9 further extend the usefulness of 1,3-dioxin vinylogous ester templates in organic synthesis. 

Oxidation of the dienolate of (17) with (+)-( ) affords a-hydroxy ester (18), a key intermediate in the enantioselective synthesis of the antibiotic echinosporin (eq 19) whereas oxidation of enolates derived from 1,3-dioxin vinylogous ester (19) gives rise to both a - and y-hydroxylation depending on the reaction conditions (eq 20). With (+)-( ) the lithium enolate of (19) gives primarily the a -hydroxylation product (20), while the sodium enolate gives )/-hydroxylation product (21). Only low levels of asymmetric induction (ca. 16% ee) are found in these oxidations. Birch reduction products are also asymmetrically hydroxylated in situ by (+)-( ) (eq 21). ... 

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