作者:Junning Lee、Jiahe Li、Shunichi Oya、John K. Snyder
DOI:10.1021/jo00046a009
日期:1992.9
The ultrasound-promoted Diels-Alder reaction of 3-methyl-4,5-benzofurandione (10) with appropriately substituted vinylcyclohexenes has led to the synthesis of tanshindiol A (9), a minor component of the Chinese traditional medicine, Dan Shen, prepared from the roots of Salvia miltiorrhiza Bunge. The regioselectivity of the cycloaddition was enhanced by the ultrasonication and was also strongly influenced by the solvent. The asymmetric synthesis of (+)-(4R)-tanshindiol A [(+)-(4R)-91, the naturally occurring enantiomer, proceeded from the optically enriched methyl 6-(benzoyloxy)-1-vinylcyclohexene-6-carboxylate [(-)-(R)-15] or 6-hydroxy-6-(hydroxymethyl)-l-vinylcyclohexene acetonide [(+)-(R)-291 (both 92% ee). Enantioselectivity in the preparation of these diene systems was accomplished by the benzoyl peroxide quench of the lithioenamine derived from methyl 1-oxocyclohexane-2-carboxylate and (S)-valine tert-butyl ester. This procedure, adapted from Koga's asymmetric alkylation of alpha-alkyl beta-keto esters, proved highly effective in preparing the necessary tertiary alcohol in protected form and with high optical purity.
Asymmetric oxidation of β-ketoesters with benzoyl peroxide; enantioselective formation of protected tertiary alcohols
作者:Junning Lee、Shunichi Oya、John K. Snyder
DOI:10.1016/s0040-4039(00)79421-4
日期:1991.10
Asymmetric oxidation of β-ketoesters by the benzoylperoxide quench of their lithioenamines formed with (S)-valine-t-butyl esters has been accomplished with good enantioselectivity for the formation of tertiary benzoate esters. This procedure thus enables generation of tertiary alcohols in protected form.
Oxidation of 1,3-dicarbonyl compounds using (camphorylsulfonyl)oxaziridines
作者:Franklin A. Davis、Hu Liu、Bang-Chi Chen、Ping Zhou
DOI:10.1016/s0040-4020(98)00500-6
日期:1998.8
The oxidation of 1,3-dicarbonyl compounds with (camphorylsulfonyl)oxaziridines 2 was studied in both cyclic and acyclic systems. Two reaction pathways were identified: enolate α-hydroxylation and a novel Baeyer-Villiger type oxidation. The Baeyer-Villiger oxidation product was observed only for the ketones and arises via rearrangement of an alkoxy epoxide. Synthetically useful ee's (82–95%) were observed