1,3-二烷氧基-乙酰丙酮和-丙酮的[1.3]σ键迁移重排

[1.3]SIGMATROPIC REARRANGEMENTS OF 1,3-DIALKYLOXY-ACETYLACETONES AND-ACETONES

1,3-二甲氧基-2-吗啉-N-基戊-1-烯-4-酮(11a)的酸水解经证实发生部分重排,生成1,3-(1a)和1,5-二甲氧基乙酰丙酮(2a)的混合物,并通过与氰基乙酰胺缩合,分别形成3-氰基-4-甲氧甲基-5-甲氧基-6-甲基吡啶-2-醇(3a)和3-氰基-4,6-双(甲氧甲基)吡啶-2-醇(4a)加以证实,前者还转化为维生素B.在相应的乙氧基序列中,除得到1b、2b、3b和4b外,还分离了反向缩合产物3-氰基-4-甲基-5-乙氧基-6-乙氧甲基吡啶-2-醇(5b).对Fedoronko等为1,3-二甲氧基丙酮的重排-水解为丙酮醛提出的烯丙型重排机制提出了质疑.事实上,这一重排更可能是一种热过程的[1.3]单键迁移过程和提供了支持的事例.

1,3-Dimethoxy-2-morpholin-N-ylpent-1-en-4-one(11a)was shown to be hydro-lyzed by acid with partial rearrangement to give a mixture of 1,3-(la)and 1,5-dime-thoxyacetylacetone(2a)which were fully identified by their condensation with cyano-acetamide to afford crystalline 3-cyano-5-methoxy-4-methoxymethyl-6-methyl-2-pyri-dinol(3a)and 3-eyano-4,6-bis(methoxymethyl)-2-pyridinol(4a)respectively.The ethoxy analogs(1b and 2b)gave besides analogous 3b and 4b also the reversed conden-sation product 3-cyano-5-ethoxy-6-ethoxymethyl-4-methy1-2-pyridinol(5b).3a was further transformed to pyridoxine(10)by standard procedures.Furthermore,1,3-dimethoxy-(12a)and 1,3-diethoxyacetone(12b)were shown to rearrange readily to respective pyruvic aldehyde aeetal(17a and 17b)while 1,3-diphenyloxy-and 1,3-diacetyloxyacetone not.These transformations were considered to be not an allylic rearra-ngement as suggested by Fedoronko and his coworkers but a[1.3]sigmatropic shift of methoxy group via their enols.