jo301327s_si_002.pdf (10.09 MB)
Asymmetric Synthesis of gem-Difluoromethylenated Dihydroxypyrrolizidines and Indolizidines
journal contribution
posted on 2012-10-05, 00:00 authored by Watcharaporn Thaharn, Teerawut Bootwicha, Darunee Soorukram, Chutima Kuhakarn, Samran Prabpai, Palangpon Kongsaeree, Patoomratana Tuchinda, Vichai Reutrakul, Manat PohmakotrAn asymmetric synthesis of gem-difluoromethylenated
dihydroxypyrrolizidines and indolizidines is described. The fluoride-catalyzed
nucleophilic addition of PhSCF2SiMe3 (1) to chiral imides was achieved in satisfactory yields to
provide mixtures of syn- and anti-isomers 6–9 with moderate to good
diastereoselectivities. Reductive cleavage of the phenylsulfanyl group
followed by intramolecular radical cyclization of the syn-isomers 6–9 occurred under refluxing
conditions to afford the corresponding gem-difluoromethylenated
1-azabicyclic compounds 10–13 in
moderate yields as a separable mixture of cis- and trans-isomers. The cis-isomers of compounds 10 and 12 and trans-13 were readily transformed to gem-difluoromethylenated
dihydroxypyrrolizidines 20 and 27 and indolizidine 28, respectively, by reductive cleavage of the hydroxyl group
and organometallic addition followed by hydrogenolysis.
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Keywords
citranrefluxing conditionsreductive cleavagecompounds 10indolizidineintramolecularchiral imidesdiastereoselectivitiecyclizationIndolizidinesAnPhSCFhydroxyl grouphydrogenolysisynthesismixtureAsymmetric Synthesisphenylsulfanyl groupsynazabicyclic2SiMeorganometallic additionnucleophilicdihydroxypyrrolizidineyieldReductive cleavageDihydroxypyrrolizidine
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