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Two-directional elaboration of hydroxyacetone under thermodynamically controlled conditions: allylation or 2-propynylation and aldol reaction.

Ishikawa T, Aikawa T, Ohata E, Iseki T, Maeda S, Matsuo T, Fujino T, Saito S

Department of Medical and Bioengineering Science, Graduate School of Natural Science and Technology, Okayama University, Tsushima, Okayama, Japan 700-8530.

Enolate generated from O-(tetrahydropyran-2-yl)hydroxyacetone under thermodynamically controlled conditions (1.3 equiv of NaH, THF, 0 degrees C to rt) was allylated at the carbon bearing the protected hydroxy group with very high regioselectively. When tert-BuOH, equivalent to the excessive portion of initially added NaH, was introduced into the mixture followed by addition of aldehyde, aldol reaction took place on the methyl group to give 1-substituted 4-hydroxy-(1E),6-heptadien-3-one in acceptable yields after acidic treatment of the mixture for dehydration and deprotection. Introducing a chiral auxiliary protecting group into hydroxyacetone led to asymmetric allylation though stereoselectivity was around 50% ee. Thus, the hidden aspect of the chemoselective nature of protected hydroxyacetone-derived enolate generated under thermodynamically controlled conditions has opened a new avenue for two-directional elaboration of hydroxyacetone that should be potentially useful in organic synthesis.

Published 15 January 2007 in J Org Chem, 72(2): 435-41.
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