Facile Access to 6-Methoxy-1,2,3,6-tetrahydro- and 4-Hydroxy-1,2,3,4-tetrahydropyridines by Electrochemical Haloalkoxylation-Dehydrohalogenation Sequence as a Key Operation
作者:Sigeru Torii、Tsutomu Inokuchi、Fumihiko Akahosi、Minoru Kubota
DOI:10.1055/s-1987-27901
日期:——
A facile procedure for the synthesis of N-ethoxycarbonyl-6-methoxy-1,2,3,6-tetrahydropyridines 6 and N-ethoxycarbonyl-4-hydroxy-1,2,3,4-tetrahydropyridines 7 from piperidines 1 is described. The electrochemical halomethoxylation of N-ethoxycarbonyl-1,2,3,4-tetrahydropyridines 4 (easily accessible from 1 by ethoxycarbonylation followed by electrooxidative methoxylation and acid-catalyzed elimination of methanol) in a CH3OH-NR4X(X = Cl, Br, I)-(Pt)-(Pt) system provides N-ethoxycarbonyl-3-halo-2-methoxypiperidines 5 in 74-90 % yields. Dehydrohalogenation of iodides 5 (X = 1) with 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) in toluene gave the desired olefin 6, which was isomerized in aqueous acetic acid to afford the alcohol 7 in 34-55% yields (from 5). The procedure is also applicable to the synthesis of seven membered derivatives 6f and 7f from 1f.
描述了一种简便的合成方法,用于制备自哌啶1衍生的N-乙氧羰基-6-甲氧基-1,2,3,6-四氢吡啶6和N-乙氧羰基-4-羟基-1,2,3,4-四氢吡啶7。在CH3OH-NR4X(X=Cl,Br,I)-(Pt)-(Pt)体系中,通过N-乙氧羰基-1,2,3,4-四氢吡啶4(可通过乙氧羰基化、电氧化甲氧基化和酸催化甲醇消除从1便捷获得)的电化学卤甲氧基化反应,以74-90%的收率得到N-乙氧羰基-3-卤-2-甲氧基哌啶5。在甲苯中使用1,8-二氮杂二环[5.4.0]十一碳-7-烯(DBU)进行碘化物5的去卤化反应(X=I),得到所需烯烃6,该烯烃在乙酸水溶液中异构化,以34-55%的收率(从5计算)提供醇7。该方法同样适用于从1f合成七元环衍生物6f和7f。