A new strategy for the preparation of an active Mn(0) and its use for radical cyclization reactions
作者:Jun Tang、Hiroshi Shinokubo、Koichiro Oshima
DOI:10.1016/s0040-4020(98)01205-8
日期:1999.2
Reduction of Li2MnCl4 with magnesium in THF afforded a fairly active manganese species which readily initiated radical cyclization of 2-iodoethanal allylic acetals at room temperature. The corresponding 2-bromoethanal acetals also provided the same cyclized products upon treatment with the activated manganese reagent at reflux in THF. This reagent can also be used to induce tandem radical cyclizations
(2) radicalcyclization, and (3) recombination of radical and manganese species giving alkylmanganese(II) compound. The reaction proved to proceed in the presence of a catalytic amount of manganese(II) chloride under atmospheric oxygen. The manganese catalyzed radicalcyclization could also be applied to 2-iodoethanal acetal, in which case the presence of oxygen was not necessary.
用锰酸三丁酯(n-Bu3MnLi 或 n-Bu3MnMgBr)处理烯丙基 2-卤代苯基醚以良好的收率提供二氢苯并呋喃衍生物。从 2-碘代苯胺化合物开始也可有效地生产二氢吲哚衍生物。该反应可以按以下顺序进行:(1)通过用三丁基锰酸(II)处理碘苯酚或碘苯胺衍生物形成自由基,(2)自由基环化,以及(3)自由基和锰物质的重组产生烷基锰(II)化合物。证明该反应在催化量的氯化锰 (II) 存在下在大气氧气下进行。锰催化的自由基环化也可以应用于 2-碘乙醛缩醛,在这种情况下,氧的存在是不必要的。
Cobalt-catalyzed carbon-carbon bond formation via radicals
Catalytic amounts of cobalt complexes 2 and 3 are capable of generating alkyl radicals from the corresponding bromides under mild readion conditions, allowing the selective preparation of either saturated or unsaturatedradicalcyclization products.
Intramolecular Radical Cyclization of 2-Haloethanal Allyl Acetal and Allyl 2-Halophenyl Ether with a Grignard Reagent in the Presence of Iron(II) Chloride
A silver-catalyzed carbomagnesiation of alkynes with alkyl halides and Grignardreagents afforded alkenyl Grignardreagentsregioselectively, where the alkyl group of the alkyl halide, but not that of the Grignardreagent, was introduced into the alkyne. Application to δ-haloalkylacetylenes yielded cyclopentanes or a tetrahydrofuran containing an exo-methylene substituent via 5-exo-dig cyclization