Intramolecular anodic olefin coupling reactions: a useful method for carbon-carbon bond formation
摘要:
The utility of intramolecular anodic olefin coupling reactions for effecting carbon-carbon bond formation has been examined. All of the successful cyclizations studied utilized either an alkyl or silyl enol ether as one of the participating olefins. The enol ethers could be coupled to simple alkyl olefins, styrenes, and allylsilanes in isolated yields ranging from 57 to 84%. The reactions were found to be effective for generating both five- and six-membered rings. The best conditions for cyclization utilized a reticulated vitreous carbon anode, constant-current conditions in an undivided cell, and a lithium perchlorate in either 50% methanol/tetrahydrofuran or 20% methanol/dichloromethane electrolyte solution. The use of an allylsilane as one of the participating olefins allowed for the regiospecific formation of olefinic products. In addition to the olefinic products, these reactions produced a small amount of a cyclized ether product in which the silyl group had not been eliminated. Deuterium-labeling studies showed that at least half of this ether byproduct arose from intramolecular migration of the methoxy group that was initially part of the starting enol ether to the carbon-beta to the silyl group. Intramolecular migration reactions of this type were found to participate in a number of the reported cyclization reactions.
Crude Drugs Effective on Visceral Larva Migrans. Part XVIII. Synthesis and Nematocidal Activity of Aralkyl- and Aralkenylamides Related to Piperamide on Second-Stage Larvae of Toxocara canis.
piperamides (3,4-methylenedioxyphenyl homologues) showed the strongest activity among the homologues tested, methoxy substituent(s) on the aromatic ring did not have much effect on the activity. However, conversion of the methoxy group to a hydroxy group greatly decreased the activity and shortened the chain length giving the strongest activity. Calculated log P values of non-phenolic aryl-piperamides fell
(MFE) on asymmetric photolysis involving a biradical intermediate have been investigated on a kinetic model where an intersystem crossing (ISC) of the intermediate is taken into account. Changes in the enantiomeric excesses (ee) of chiral substances with circularly polarized light (CPL) irradiation have been simulated, and the necessary conditions for observing the MFE were obtained. The asymmetric photolysis
conditions atom transfer products (17a–c, 18c,d) were obtained exclusively, whose regio- and stereochemistry were dependant on the olefinic acceptor. Thus, irradiation of the ester trans-16a or the phenyl derivative 16b (E/Z mixture) gives the trans-cyclopentyl derivatives 17a and 17b; the bromide 16c (R=Me) affords a mixture of the trans-cyclopentyl compound 17c and a comparable amount of the cyclohexyl
Oxidative Cyclization of Unsaturated Ketene Dithioacetals with Ceric Ammonium Nitrate to Form Bicyclic Lactones
作者:Barry B Snider、Bo Shi、Cheri A Quickley
DOI:10.1016/s0040-4020(00)00857-7
日期:2000.12
Ceric ammonium nitrate oxidizes unsaturated ketene dithioacetals in wet MeCN to give cation radicals that cyclize to tri-substituted double bonds and styrenes by cation-like cyclizations leading to cyclic cation radicals that are transformed by further oxidation, hydrolysis and cyclization to bicyclic lactones in moderate to good yield. (C) 2000 Elsevier Science Ltd. All rights reserved.
Synthesis of Cyclic Ketones by Electrochemical Reduction of <i>S</i>-(2-Methoxycarbonyl)phenyl Thiolesters