201420-68-0Relevant articles and documents
Stereo- And Regioselective Introduction of 1- or 2-Hydroxyethyl Group via Intramolecular Radical Cyclization Reaction with a Novel Silicon-Containing Tether. An Efficient Synthesis of 4′α-Branched 2′-Deoxyadenosines
Shuto, Satoshi,Kanazaki, Makiko,Ichikawa, Satoshi,Minakawa, Noriaki,Matsuda, Akira
, p. 746 - 754 (2007/10/03)
An efficient method for the synthesis of 4′α-branched 2′-deoxyadenosines starting from 2′-deoxyadenosine has been developed utilizing a novel radical cyclization reaction with a silicon tether. The radical reaction of 4′β-(phenylseleno)-3′-O-diphenylvinylsilyl adeninenucleoside derivative 17 with Bu3SnH and AIBN, followed by Tamao oxidation, gave selectively either the 4′α-(2-hydroxyethyl) derivative 21 or 4′α-(1-hydroxyethyl) derivative 19, depending on the reaction conditions. With a lower Bu3SnH concentration, the reaction gave the 4′α-(2-hydroxyethyl) derivative 21, via a 6-endo-radical cyclized product 20, as the sole product in 72% yield. The reaction of 17 in the presence of excess Bu3SnH gave 19 quantitatively, via a 5-exo-cyclized product 18, as a diastereomeric mixture. The reaction mechanism was examined using Bu3SnD. The results demonstrated that the 5-exo cyclized (3-oxa-2-silacyclopentyl)methyl radical (C) was formed initially which was trapped when the concentration of Bu3SnH(D) was high enough. With lower concentrations of Bu3SnHCD), radical C rearranged into the ring-enlarged 4-oxa-3-silacyclohexyl radical (D) which was then trapped with Bu3SnH(D) to give endo-cyclized product F.
