Stereoselective vinylogous Mannich reaction of 2-trimethylsilyloxyfuran with L-gulose-derived chiral nitrones in the presence of a catalytic amount of trimethylsilyl trifluoromethanesulfonate was investigated. The selectivity was strongly influenced by the bulkiness of the C-substituent of the nitrone: for example, C-benzyloxymethyl nitrone afforded four stereoisomers, whereas bulky C-[(4S)-2,2-dimethyl-1,3-dioxolan-4-yl]nitrone gave a single stereoisomer. The latter product was elaborated to afford key synthetic intermediates for polyoxin C and dysiherbaine.
研究人员在催化剂量的
三氟甲磺酸三甲基硅酯存在下,研究了 2-三甲基
硅氧基
呋喃与 L-
古洛糖衍生的手性腈的立体选择性
乙烯基曼尼希反应。腈酮的 C-取代基的体积对选择性有很大影响:例如,C-苄氧基
甲基腈酮可生成四种立体异构体,而体积较大的 C-[(4S)-2,2-二甲基-
1,3-二氧戊环-4-基]腈酮只能生成一种立体异构体。对后一种产品进行了详细加工,以获得聚氧
乙烯醚 C 和地西海因的关键合成中间体。