Origin of Chiral Induction in Radical Reactions with the Diastereoisomers (5R)- and (5S)-5-l-Menthyloxyfuran-2[5H]-one
摘要:
Acetalization of 5-hydroxyfuran-2[5H]-one with l-menthol yields (5R)-(1) and (5S)-5-l-menthyloxyfuran-2[5H]-one (2) in equal amounts. The diastereomer 1 crystallizes preferentially. For the first time, the isolation of pure diastereoisomer 2 is reported. Different diastereoselectivities were observed in the radical tandem reaction of 1 and 2 with N,N-dimethylaniline. The privileged conformations in solution of the substrates and the products of the radical reaction were then determined, and X-ray crystal structure analyses were carried out on the reaction products. The different stereoselectivities in both cases are explained by different orientations of the menthyloxy substituent.
Stereoselective radical-tandem reaction of aniline derivatives with (5R)-5-menthyloxy-2,5-dihydrofuran-2-one initiated by photochemical induced electron transfer
Diastereoselective Radical Tandem Addition-Cyclization Reactions of Aromatic Tertiary Amines by Semiconductor-Sensitized Photochemical Electron Transfer
作者:Siniša Marinković、Norbert Hoffmann
DOI:10.1002/ejoc.200400102
日期:2004.7
The diastereoselective radicaltandemaddition-cyclizationreaction of N,N-dimethylaniline (2) with menthyloxyfuranone 1 was initiated by photochemically induced electron transfer using inorganic semiconductors (TiO2, ZnS, SiC and SnO2) as sensitizers. The rearomatization step, which also causes the partial reduction of 1, was studied by isotopic labeling experiments using deuterated derivatives of
Diastereoselective Tandem Addition−Cyclization Reactions of Unsaturated Tertiary Amines Initiated by Photochemical Electron Transfer (PET)
作者:Samuel Bertrand、Norbert Hoffmann、Stéphane Humbel、Jean Pierre Pete
DOI:10.1021/jo001166l
日期:2000.12.1
Polycyclic molecules and tetrahydroquinoleines were obtained in a tandem reaction involving the diastereoselective addition of or-aminoalkyl radicals to (5R)-5-menthyloxy-2[5H]-furanone 1. The facial diastereoselectivity on 1 is greater than or equal to 90%. The alpha -aminoalkyl radicals were produced from tertiary amines by photachemical-induced electron transfer. When N,N-dialkylanilines 19 were used as starting tertiary amines, a rearomatization step was involved and important side reactions of 1 were observed. A mechanistic study involving isotopic labeling of the starting amine indicated that the byproducts resulted from reduction of 1 during the rearomatization process. An efficient optimization of the reaction was obtained by simply adding acetone or cyclopentanone as mild oxidants to the reaction mixture. The side products resulting from reduction of the furanone 1 were completely suppressed under these conditions, and the yields of the tettahydroquinolines 21a-i, 22a-f, and 26g-i were doubled.
Origin of Chiral Induction in Radical Reactions with the Diastereoisomers (5<i>R</i>)- and (5<i>S</i>)-5-<i>l</i>-Menthyloxyfuran-2[5<i>H</i>]-one
Acetalization of 5-hydroxyfuran-2[5H]-one with l-menthol yields (5R)-(1) and (5S)-5-l-menthyloxyfuran-2[5H]-one (2) in equal amounts. The diastereomer 1 crystallizes preferentially. For the first time, the isolation of pure diastereoisomer 2 is reported. Different diastereoselectivities were observed in the radical tandem reaction of 1 and 2 with N,N-dimethylaniline. The privileged conformations in solution of the substrates and the products of the radical reaction were then determined, and X-ray crystal structure analyses were carried out on the reaction products. The different stereoselectivities in both cases are explained by different orientations of the menthyloxy substituent.
Stereoselective radical-tandem reaction of aniline derivatives with (5R)-5-menthyloxy-2,5-dihydrofuran-2-one initiated by photochemical induced electron transfer
The radical tandem reaction of simple alkyl derivatives of aniline to a chiral furanone can be carried out stereoselectively in high yields; the furanone is also involved as oxidant in a rearomatisation process (formation of byproducts) where it can be replaced efficiently by acetone.