Studies on tandem transesterification and intramolecular cycloaddition of nitrones. 1. Sequential bicyclization of α-methoxycarbonylnitrones with allyl alcohols
摘要:
Treatment of alpha-methoxycarbonylnitrones with 5 equiv. of allyl alcohols in the presence of 1 equiv. of titanium tetraisopropoxide causes tandem transesterification, E,Z-isomerization of the nitrone moieties, and intramolecular cycloaddition to afford bicyclized compounds in one step. To reduce amounts of allyl alcohol, combined use of a catalytic amount of titanium tetraisopropoxide and molecular sieves 4A was found to be a more improved catalytic system, It was also found that reactions of (Z)-allyl alcohols with alpha-methoxycarbonylnitrone ate more facile than those of (E)-allyl alcohols. This aspect was extended to geometry differentiated cycloaddition.
Reaction design in asymmetric catalysis has traditionally been predicated on a structurally robust scaffold in both substrates and catalysts, to reduce the number of possible diastereomeric transition states. Herein, we present the stereochemical dynamics in the Ni(II)-catalyzed diastereoconvergent (3 + 2) cycloadditions of isomerizable nitrile-conjugated nitrones with α-ketoesterenolates. Even in
An alternative enantioselective total synthesis of (+)-monomorine I
作者:Masayuki Ito、Chihiro Kibayashi
DOI:10.1016/s0040-4039(00)97807-9
日期:1990.1
An alternative enantioselective total synthesis of (+)-monomorine I has been achieved, based on asymmetric nitrone cycloaddition using a chiral allyl ether.
Total synthesis of (+)-monomorine I via nitrone cycloaddition route
作者:Masayuki Ito、Chihiro Kibayashi
DOI:10.1016/s0040-4020(01)80881-4
日期:1991.11
enantioselective total synthesis of (+)-monomorine I (1) is described. The key feature of the synthesis is the asymmetric 1,3-dipolar cycloaddition of the prochiral nitrone 9 with the chiral (S)-allylic ether 8 as a dipolarophile, which provides stereoselectively the C-3,C-5-trans-isoxazolidine 10 with the correct relative and absolute stereochemistry suitable for the synthesis of (+)-monomorine I.
Catalytic Migratory Oxidative Coupling of Nitrones
作者:Shogo Hashizume、Kounosuke Oisaki、Motomu Kanai
DOI:10.1021/ol201629n
日期:2011.8.19
bond-formation proceeds through cleavage of two C(sp3)–H bonds concomitant with C═N double bond-migration. The reaction provides an alternating nitrone moiety, allowing for further synthetically useful transformations. Radical clock studies suggest that the nucleophilicaddition of nitrones to an oxidatively generated carbocation is a key step.
Catalytic migratory oxidative coupling of nitrones through an outer-sphere C(<i>sp<sup>3</sup></i>)-H activation process
作者:Shogo Hashizume、Kounosuke Oisaki、Motomu Kanai
DOI:10.1002/tcr.201100024
日期:2011.9.29
efficient C‐Hactivation, which has attracted increased interest in organic chemistry. In this account, we describe a CuI‐catalyzed oxidative coupling between nitrones and various ethers or amines as an example. Predictable site‐selective C‐C bond formation was achieved throughactivation of the C‐H bonds in each coupling partner and the migration of a C‐N double bond. Mechanisticstudies strongly suggested