Concise Synthesis of α-Substituted 2-Benzofuranmethamines and Other 2-Subsituted Benzofurans via α-Substituted 2-Benzofuranmethyl Carbocation Intermediates
作者:Nikhom Wongsa、Ubonta Sommart、Thunwadee Ritthiwigrom、Arife Yazici、Somdej Kanokmedhakul、Kwanjai Kanokmedhakul、Anthony C. Willis、Stephen G. Pyne
DOI:10.1021/jo302554v
日期:2013.2.1
Propargyl amines 4, where R3 is aryl, undergo 5-exo-dig cyclization reactions under relatively mild conditions (AgNO3, DMF, 60 °C, 1 h) to give 3-amino-2,3-dihydro-2-arylmethylidenebenzofurans 5 (R3 = aryl). In contrast, substrates where R3 is alkyl undergo competing 6-endo-dig and 5-exo-dig cyclization processes. The hydroxymethyl substrate 4 (R3 = CH2OH), however, was smoothly converted to its corresponding
在相对温和的条件下(AgNO 3,DMF,60°C,1小时),炔丙基胺4(其中R 3为芳基)经历5- exo - dig环化反应,得到3-氨基-2,3-二氢-2-芳基亚甲基苯并呋喃5(R 3=芳基)。相反,其中R 3是烷基的底物经历竞争的6-内切-挖掘和5-外切-挖掘环化过程。羟甲基片4(R 3 = CH 2 OH),然而,顺利转化为其相应的5-外型-挖环化产物5,可能是由于伯羟基基团的在5-协助外-挖环化方法由银阳离子的协调。在更严格的条件下(AgNO 3,DMF,100°C,18 h),最初形成的产品5进行1,3-烯丙基重排为其相应的2-取代的苯并呋喃衍生物6。这种重排也可以通过在DMF中用AgNO 3在100°C下处理5 h或在室温下用BF 3 ·Et 2 O处理5来实现。2-(3-丁烯基)苯并呋喃7(Nu =烯丙基)可以通过处理5含BF 3 ·Et 2 O和烯丙基三丁基锡烷。在这些BF