Cycloaromatization of α-Oxoketene Dithioacetals with 5-Lithiomethyl-3-methylisoxazole: A New General Method for the Synthesis of Substituted and Annulated 1,2-Benzisoxazoles
A new route to 6-substituted 4a-e and 5,6-annulated 4f-l 1,2-benzisoxazoles has been developed through regioselective 1,2-nucleophilic addition of 5-lithiomethyl-3-methylisoxazole (2) to a variety of α-oxoketene dithioacetals 1a-l and subsequent cycloaromatization of the resulting hydroxyacetals in the presence of boron trifluoride -diethyl ether complex. The corresponding 4-dethiomethylated benzisoxazoles 6a-d were also synthesized by cyclocondensation of β- methylthio-α,β-unsaturated ketones with 2 under identical conditions. The reaction was further extended for the synthesis of (6-benzisoxazolyl)-substituted ethylenes 9a-e, butadienes 9f-g and hexatriene 9h by subjecting α-cinnamoyl ketene dithioacetals 7a-e and their higher enyl analogs 7f-h to similar transformations.
Partial Reductive Demethylthiolation of<i>a</i>-Ketoketene<i>S,S</i>-Acetals with Sodium Borohydride/Nickel Chloride: A New, General Method for 2-Methylthio-1-alkenyl Ketones
作者:B. Myrboh、L. W. Singh、H. Ila、H. Junjappa
DOI:10.1055/s-1982-29791
日期:——
RAO, CH. SRINIVASA;CHAKRASALI, R. T.;ILA, HIRIYAKKANAVAR;JUNJAPPA, HIRIYA+, TETRAHEDRON, 46,(1990) N, C. 2195-2204
作者:RAO, CH. SRINIVASA、CHAKRASALI, R. T.、ILA, HIRIYAKKANAVAR、JUNJAPPA, HIRIYA+
DOI:——
日期:——
MYRBOH, B.;SINGH, L. W.;ILA, H.;JUNJAPPA, H., SYNTHESIS, BRD, 1982, N 4, 307-309
作者:MYRBOH, B.、SINGH, L. W.、ILA, H.、JUNJAPPA, H.
DOI:——
日期:——
Regio- and chemoselective conjugate 1,4-reduction of α-oxoketene dithioacetals with sodium borohydride and sodium cyanoborohydride
Theα-oxoketene dithioacetals are shown to undergo conjugate 1,4-reduction in highly regio- and chemoselective manner with sodium borohydride in acetic acid to afford the corresponding β-oxodithioacetals in good yields. These results have been rationalized according to HSAB principle in terms of 'hard soft affinity inversion' concept. The reduction of with sodium cyanoborohydride also proceeds in 1