Metalation and Electrophilic Quenching of C-4 Functionalized Isoxazoles; VIII. Preparation of Derivatives of 5-Thioalkylisoxazoles
作者:T. N. Balasubramaniam、Yousef R. Mirzaei、N. R. Natale
DOI:10.1055/s-1990-27099
日期:——
The lateral metalation and electrophilic quenching of isoxazoles bearing electron withdrawing groups in the 4-position 1 with disulfides, represents a selective, direct and synthetically useful entry to the thioalkyl derivatives 2 (nine examples). One exception to the formation of monothioalkyl major products was observed for the dianion of 4-[(2-hydroxymethyl-1-pyrrolidinyl)carbonyl]-3,5-dimethylisoxazole (1i) which was found to produce the 5-[bis(phenylthio)methyl]isoxazole derivative 3i as the major isolated product (66%). Oxidation of 2a with 3-chloroperoxybenzoic acid (MCPBA) proceeds selectively at sulfur in the presence of both isoxazole and oxazoline nitrogens to give the corresponding sulfoxide 4a (56%) or sulfone 5a (72%), respectively.
Regiospecific Control of Additions of 4-Substituted 3,5-Dimethylisoxazoles to α,β Unsaturated Carbonyls
作者:J. R. Stenzel
DOI:10.1055/s-1997-1315
日期:1997.9
Transmetalation of C-5-lithiomethylisoxazoles with the lower-order cuprate reagent lithium thienylcyanocuprate (Li[ThCuCN]) in THF results in exclusive conjugate addition to α,β-unsaturated carbonyls. In contrast, transmetalation with samarium tris(hexamethyldisilazide) (Sm[HMDS]3) in diethyl ether directs 1,2-carbonyl addition. In both cases, optimum results were realized with a 4,5-dihydro-4,4-dimethyl-Π2-oxazoline substituent at the C-4 position of the isoxazole.