Lewis Acid Promoted Rearrangements of 1,3-Dioxolanyl-Substituted 1,2-Oxazines into Novel Products with 1,3,6-Trioxa-7-azacyclopenta[<i>cd</i>]indene Skeletons
作者:Hans-Ulrich Reissig、Fabian Pfrengle、Ahmed Al-Harrasi
DOI:10.1055/s-2006-956463
日期:2006.12
Lewis acid promoted rearrangements of 4-methoxy- and 4-benzyloxy-substituted 1,2-oxazines syn-1b and syn-1c furnished novel tricyclic products 5 and 6. A mechanistic rationale is suggested for the different rearrangement pathways depending on the configuration and the nature of the 4-alkoxy groups of the precursor 1,2-oxazines. Short period hydrogenolyses of these rearrangement products afforded tetrahydrofuranyl-annulated 5,6-dihydro-4H-1,2-oxazines 10 and 11, whereas longer reduction times led to formation of tetrahydrofuran derivatives 14, 15 and 16, 17 in good yields.
在路易斯酸的促进下,4-甲氧基和 4-苄氧基取代的 1,2-噁嗪 syn-1b 和 syn-1c 发生重排,生成了新型三环产物 5 和 6。根据前体 1,2-噁嗪中 4-烷氧基基团的构型和性质,提出了不同重排途径的机理依据。对这些重排产物进行短时间的氢解,可得到四氢呋喃基环化的 5,6- 二氢-4H-1,2-噁嗪 10 和 11,而较长的还原时间则可形成四氢呋喃衍生物 14、15 和 16、17,而且产率很高。