Influence of quaternization or coordination of nitrogen with a Lewis acid upon the diastereoselectivity of 5-exo ring closure of β-aminoalkyl radicals
摘要:
Two methodologies, likely to enhance the diastereoselectivity of sulfonyl radical mediated cyclization of dienes 8 and 11, were investigated. Quaternization provided the expected result whatever the nature of the radical accepting. double bond, so did complexation of 11 with BF3 or AlMe3. A more strongly coordinating reagent like BH3 was necessary to improve selectivity in the case of 8. (C) 1998 Elsevier Science Ltd. All rights reserved.
Influence of quaternization or coordination of nitrogen with a Lewis acid upon the diastereoselectivity of 5-exo ring closure of β-aminoalkyl radicals
摘要:
Two methodologies, likely to enhance the diastereoselectivity of sulfonyl radical mediated cyclization of dienes 8 and 11, were investigated. Quaternization provided the expected result whatever the nature of the radical accepting. double bond, so did complexation of 11 with BF3 or AlMe3. A more strongly coordinating reagent like BH3 was necessary to improve selectivity in the case of 8. (C) 1998 Elsevier Science Ltd. All rights reserved.
Three different routes for the stereoselectivesynthesis of botryodiplodin have been investigated. The intramolecular allylation of acetals proved to be unsatisfactory due to unstable intermediates and poor stereocontrol. Zard intramolecular radical allylation of a 2-iodopropionate derivative allows the development of an expeditious synthesis of racemic botryodiplodin. The relative configuration within
(±)-botryodiplodin (1). Several pathways, involving 5-exo-trig ring closure onto allylic sulfones, have been investigated. The iodine atom transfer methodology allowed the preparation of the desired skeleton through intramolecular addition of an α-alkoxycarbonyl radical to the double bond of the appropriate allylic ethyl sulfone. Subsequent deprotonation and kinetic reprotonation led to the key precursor14 with
4-Isopropenyl-3-tosylmethyl pyrrolidines through radical cyclizations of 4-aza-1,6-dienes - an approach to kainic acids
作者:M.-P Bertrand、S Gastaldi、R Nouguier
DOI:10.1016/0040-4039(96)00006-8
日期:1996.2
The cyclofunctionalization of 4-aza-1,6-dienes 1 and 2 - bearing a prenyl chain - via the radical addition of PhSeTs (4) has been investigated as a potential route to 4-isopropenyl-3-tosylmethylpyrrolidines. Since the oxidative elimination of the resulting selenides afforded mainly the undesired olefinic regioisomer, an alternative pathway via the rearrangement of allylic sulfones 10–11, was applied