✍ Scribed by Eun Lee; Jin-wook Jeong; Yunjae Yu
No coin nor oath required. For personal study only.
Radical cyclization of I~-alkoxyacrylates is now firmly established as an effective method in forming 5-or 6-membered oxacycles, l The value of this reaction lies in the fact that only cis-2,5-disubstituted tetrahydrofurans and cis-2,6-disubstituted tetrahydropyrans are obtained when [~-alkoxyacrylates prepared from secondary alcohols are used as substrates. This stereoselectivity may be explained by invoking preference for the s-trans(C~-O) transition state geometryJ a More recently, examples of diastereoselective carbocycle formation were reported, in which acrylate substrates containing various chiral auxiliary alcohols were used in radical cyclization reactions. 2 Use of [3-alkoxyacrylates obtained from achiral primary alcohols and chiral propiolates may also result in useful degrees of diastereoselection in oxacycle synthesis, and this report concerns our initial results in these areas of studies.
The use of/-menthol as the chiral auxiliary generally did not lead to noticeable degree of diastereoselection. 3 But in the case of the aldehyde 1, 19 % d.e. of the tetrahydropyranyl product 2 was obtained and the lactone product 3 was obtained in 28 % e.e. (Scheme 1). Ii O O O 2 3 1 47 % (19 % d.e.) 42 % (28 % e.e.) a) 1.3 eq. Bu3SnH, 0.15 eq. AIBN,Benzene (0.03 M), Reflux, 8 h Scheme 1
In both cases, the diol products, which were obtained after LAH reduction, were derivatized with TBSC1 and (S)-O-acetylmandelyl chloride, and d.e. of each compound was determined by NMR analysis 4 (Scheme 2).
📜 SIMILAR VOLUMES
## Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.
trans-Kumausyne was synthesized from D-(+)-xylose. Radical cycLization reaction of a I]-alkoxyacrylate intermediate proceeded stereoselectively to give a tetrahydrofuranyl product with correct stereochemistry.
Radical cyclization reaction of a bis(~-alkoxyacrylate) intermediate prepared from (-)-diethyl D-tartrate proceeded stereoselectively to give a 2,6-dioxabicyclo[3.3.0]octane product, which was converted into a known intermediate in the synthesis of kumausallene.