Intramolecular cyclization of 1-nitroalkenyl radicals generated by one-electron oxidation of aci-nitro anions with CAN: stereoselective formation of 3,4-functionalized tetrahydrofurans

Abstract

Upon one-electron oxidation by ammonium hexanitratocerate(iv) (CAN), aci-nitro anions 3a-d resulting from oxa-Michael addition of allylic alcohol to a,b-disubstituted nitroalkenes 1a-d undergo stereoselective radical cyclization into 3-nitro-4-nitrooxymethyltetrahydrofurans 6a-d and 3-nitro-4-hydroxymethyltetrahydrofurans 7,8a-d.

Intramolecular6-exoCyclization of 1-Nitro-6-heptenyl Radicals Generated by One-Electron Oxidation ofAci-Nitroanions with CAN: A Completely Stereoselective Formation of 2,3,4-Trisubstituted Tetrahydropyrans

“…Since in turn, 5-hexenyl analogs undergo cyclization via a favoured cis-fused bicyclic nitroxyl to afford by subsequent ligand exchange exo nitratomethyl esters, 1 we can postulate that the relative orientation of the nitro group and the newly generated alkyl radical resulting from cyclization of 1-nitroalkenyl radicals plays an important role in controlling the outcome of the reaction. These relative orientations are ring size dependent and govern both the stereochemistry and the further transformation of the newly generated alkyl radical to provide either exo 4-nitratomethyl tetrahydrofurans or endo 4-methyl tetrahydropyrans.…”

“…1 In this ammonium hexanitratocerate (IV) (CAN) promoted one-electron oxidation, direct reduction by the solvent of alkyl radicals resulting from 5-exo cyclization was not observed. 1 In this ammonium hexanitratocerate (IV) (CAN) promoted one-electron oxidation, direct reduction by the solvent of alkyl radicals resulting from 5-exo cyclization was not observed.…”

ChemInform Abstract: Intramolecular 6‐exo Cyclization of 1‐Nitro‐6‐heptenyl Radicals Generated by One‐Electron Oxidation of aci‐Nitroanions with CAN: A Completely Stereoselective Formation of 2,3,4‐Trisubstituted Tetrahydropyrans.

“…Alternatively, trisubstituted tetrahydropyrans 6a-d could be obtained directly from 1a-d, according to a one-pot process; in this case, due to the slight excess of 3-buten-1ol, 3-butenyloxy-2-tetrahydrofuran was isolated (8-10%) as by product. 11 Although the yields have not been optimized, other isomers could not be detected by 1 H NMR analysis of the crude reaction mixtures.…”

“…We recently disclosed a general conversion of nitroalkene derivatives into functionalized tetrahydrofurans via intramolecular radical carbocyclization of a-substituted ballyloxy nitro compounds. 1 In this ammonium hexanitratocerate (IV) (CAN) promoted one-electron oxidation, direct reduction by the solvent of alkyl radicals resulting from 5-exo cyclization was not observed. But, in turn, a stereoselective cyclization leading to exo nitrate esters as major compounds occurred (Scheme 1).…”

Oxidative cyclization in the synthesis of 5‐ and 6‐membered N,O‐heterocycles

“…Intramolecular CAN-promoted radical carbocyclization of ␣-substituted ␤-allyloxy nitro compounds 342 leads to functionalized THFs 344 and 345 (Scheme 78) [165].…”