Control of Dispersity and Stereochemistry in Free Radical Telomerizations: A Radical Addition, Cyclization, Chain Transfer (ACT) Strategy

Abstract

A general strategy for the stereoselective preparation of n = 2 telomers displaying narrow dispersity is reported. Covalent assemblies composed of a rigid base compound, flexible tethers, and oxazolidine acrylamide monomers were reacted under free radical conditions to afford macrocyclic precursors to the targeted telomers through an addition, cyclization, chain transfer (ACT) sequence. Subsequent hydrolysis and esterification afforded the desired products with excelient stereoselectivity and teloselectivity. Systematicvariation of system components (the rigid base compound, the functionality linking base compound to the tethers, the length of the tethers, the configuration at the site of oxazolidine attachment, and the auxiliary blocking group) allowed for identification of the structural elements necessary for successful implementation. It was found that each of these variables had a marked influence on the performance of the covalent assembly.Many synthetically interesting target molecules contain skeletal fragments that are comprised in part of a finite number of repetitive chiral segments. Examples containing multiple consecutive propionate units include (-)-lardohre 1, the aggression pheromone of the acarid mite Lardoglyphus konoi,' and 2, a compound isolated from the preen-gland wax of the domestic goose Anser a.f. domesticus.2

A Simple and Cost Effective Synthesis of 3,11-Dimethylnonacosan-2-one, A Female Sex Pheromone of the German Cockroach

“…Compound 6 was oxidized by Jones reagent at 0 °C in acetone to generate acid 7 in 80% yield [9], which was then treated with methyllithium (1.4 M solution in ether) in THF to give 9-bromononan-2-one (8) in 64% yield [10]. Bromination of alcohol 9 was performed with phosphorus tribromide in ether to produce a 95% yield of bromide 10, which was treated with Li metal in dry THF to yield anion 11, which was coupled in situ with bromide 8 [11] in DMF to generate tertiary alcohol 12 in 60% yield for two steps. In this bromination reaction the alternate CBr 4 /PPh 3 method proved to be relatively low yielding (80%) [12].…”