CYCLIZATIONS OF UNSATURATED.CR(COX)2 RADICALS - MANGANESE(III) ACETATE OXIDATIVE CYCLIZATIONS OF UNSATURATED ACETOACETATES AND ATOM-TRANSFER CYCLIZATIONS OF UNSATURATED HALOACETOACETATES GIVE THE SAME RADICALS
CYCLIZATIONS OF UNSATURATED.CR(COX)2 RADICALS - MANGANESE(III) ACETATE OXIDATIVE CYCLIZATIONS OF UNSATURATED ACETOACETATES AND ATOM-TRANSFER CYCLIZATIONS OF UNSATURATED HALOACETOACETATES GIVE THE SAME RADICALS
复制标题
DOI：
10.1021/ja00017a037
复制
发表时间：
1991-08-14
影响因子：
15
通讯作者：
DOMBROSKI, MA
中科院分区：
文献类型：
--
作者：
CURRAN, DP;MORGAN, TM;DOMBROSKI, MA
比较区域和立体化学的结果时，得到一系列的2-取代的3-氧代-庚-6-烯酸（或辛-7-烯酸）酯（乙酰乙酸酯）的环化进行锰（III）乙酸氧化或碘或溴原子转移环化。观察到的趋势支持的结论，自由基6 b（而不是Mn（III）络合的自由基5 b）参与Mn（III）介导的氧化环化叔丙二酸酯和乙酰乙酸酯。大多数环化反应在动力学控制下进行，有几个表现出很大的温度依赖性的立体选择性。通过证明自由基43的开环（反向6-exo环化）比溴转移快，但比碘转移或Cu（II）氧化慢，解决了一个明显的差异。在闭环/开环过程中，Z-烯烃转化为E-烯烃。由于E-和Z-烯烃提供不同的立体化学环化的结果，观察到的立体化学比成为一个非常敏感的探针，这种自由基开环。这一观察结果预示着设计和使用相关探针进行自由基开环。
Comparable regio- and stereochemical results were obtained when cyclizations of a series of 2-substituted 3-oxo-hept-6-enoate (or oct-7-enoate) esters (acetoacetates) were conducted by manganese(III) acetate oxidation or by iodine or bromine atom transfer cyclization. The observed trends support the conclusion that free radicals 6b (rather than Mn(III)-complexed radicals 5b) are involved in the Mn(III)-mediated oxidative cyclization of tertiary malonates and acetoacetates. Most cyclizations proceeded under kinetic control, and several showed large temperature dependences on stereoselectivity. An apparent discrepancy was resolved by demonstrating that ring opening of radical 43 (a reverse 6-exo cyclization) was faster than bromine transfer, but slower than iodine transfer or Cu(II) oxidation. In the process of ring closure/ring opening, a Z-alkene is converted to an E-alkene. Since the E- and Z-alkenes provide distinct stereochemical results on cyclization, the observed stereochemical ratio becomes a very sensitive probe for this radical ring opening. This observation presages the design and use of related probes for radical ring opening.