Ring-enlargement reaction of alkylidenecarbenes bearing a cyclic ether or acetal group. Formation of medium-sized cyclic enol ethers or dienol ethers via bicycloalkenyloxonium ylides
作者:Takashi Mori、Masahiko Taniguchi、Fumito Suzuki、Hisashi Doi、Akira Oku
DOI:10.1039/a803078b
日期:——
The reaction of 2-acetonyltetrahydrofuran 1a and 2-acetonyltetrahydropyran 1b with the potassium salt of dimethyl diazomethylphosphonate (DAMP) in the presence of MeOH produced ring enlargement product 1-methyl-3-oxacyclooctene 6a (22%) and 1-methyl-3-oxacyclononene 6b (28%), respectively, in addition to nonrearranged products. When the side-chain was elongated by one carbon unit (1c), ring enlargement did not take place. Analogous reactions of 2-acetonyl-substituted 1,3-dioxolane 9a, 1,3-dioxane 9b and 1,3-dioxepane 9c also produced, respectively, 3,5-dimethyl-1,6-dioxacycloocta-2,4-diene (16a, 58%), a mixture (combined yield 83%) of 3,5-dimethyl-1,6-dioxacyclonona-2,4-diene (16b) and 5-exo-methylene-3-methyl-1,6-dioxacyclonon-2-ene (17b), and a mixture (combined yield 54%) of 3,5-dimethyl-1,6-dioxacyclodeca-2,4-diene (16e) and 5-exo-methylene-3-methyl-1,6-dioxacyclodec-2-ene (17e). Side-chain-elongated dioxolane 9d did not undergo enlargement and, instead, ring-switched product 3,6-dimethyl-6-[2-(tert-butyloxy)ethoxy]-5,6-dihydropyran 22 was formed. The formation of products 6, 16, 17 and 22 can be explained in terms of the intermediacy of bicyclooxonium ylides, which are formed in an intramolecular manner between the alkylidenecarbene and a cyclic ether or cyclic acetal unit. In most reactions of acetonyl-substituted cyclic acetals, the major products were di(enol ether)s 16 and 17 even in the presence of a protic nucleophile such as MeOH. A reversible intramolecular process between alkylidenecarbenes and ylides is also proposed.
2-乙酰基四氢呋喃1a和2-乙酰基四氢吡喃1b与二甲基重氮甲基膦酸钾盐(DAMP)在甲醇存在下的反应分别生成了环扩张产物1-甲基-3-氧杂环辛烯6a(22%)和1-甲基-3-氧杂环壬烯6b(28%),以及未重排的产物。当侧链延长一个碳单位(1c)时,没有发生环扩张。2-乙酰基取代的1,3-二氧杂环戊烷9a、1,3-二氧杂环己烷9b和1,3-二氧杂环庚烷9c的类似反应分别生成了3,5-二甲基-1,6-二氧杂环辛-2,4-二烯(16a,58%)、3,5-二甲基-1,6-二氧杂环壬-2,4-二烯(16b)和5-外-亚甲基-3-甲基-1,6-二氧杂环壬-2-烯(17b)的混合物(总产率83%),以及3,5-二甲基-1,6-二氧杂环癸-2,4-二烯(16e)和5-外-亚甲基-3-甲基-1,6-二氧杂环癸-2-烯(17e)的混合物(总产率54%)。侧链延长的二氧杂环戊烷9d没有发生环扩张,而是生成了环转换产物3,6-二甲基-6-[2-(叔丁氧基)乙氧基]-5,6-二氢吡喃22。产物6、16、17和22的形成可以通过双环氧翁叶立德的中间体来解释,这些中间体是通过烷基亚甲基卡宾和环醚或环缩醛单元之间的分子内方式形成的。在大多数乙酰基取代的环缩醛的反应中,即使在甲醇等质子性亲核试剂存在下,主要产物也是二烯醇醚16和17。还提出了烷基亚甲基卡宾和叶立德之间的可逆分子内过程。