N-(3-Benzo[b]thienyl)iminophosphoranes toward the Synthesis of Benzo[b]thieno[3,2-b]pyridines: Reactivity and Alternative Regioselectivity with α,β-unsaturated Ketones and Aldehydes
es 1b–d react with α,β-unsaturated aldehydes and ketones 2a–e to give varying mixtures of the regioisomeric benzothieno[3,2-b]pyridines 3a–d and 4a–d as a result of preferential attack of either imino nitrogen or α-thienyl carbon at the enone carbonyl group. The findings indicate that the progressive replacement of phenyl with methyl P-substituent greatly enhances the reactivity of the phosphorane
新的N-(3-苯并[ b ]噻吩基)亚氨基正膦酸酯1b - d与α,β-不饱和醛和酮2a - e反应,生成区域异构的苯并噻吩并[3,2- b ]吡啶3a - d和亚氨基氮或α-噻吩基羧酸在烯酮的羰基上优先进攻的结果是在图4a - d中。该发现表明,用甲基P-取代基逐步取代苯基大大增强了磷烷1的反应性。 并同时提高了磷烷本身通过α-噻吩基碳添加到烯酮中的倾向。
New entry to benzo[b]thieno[2,3-b]- and benzo[b]thieno-[3,2-b]-pyridines using 2- and 3-azidobenzo[b]thiophene as the nitrogen precursors
N-(3-Benzo[b]thienyl)- and N-(2-benzo[b]thienyl)-imino-triphenylphosphorane—prepared from the corresponding azidobenzo[b]thiophenes—react with α,β-unsaturated aldehydes under mild conditions to give directly benzo-[b]thieno[3,2-b]- and benzo[b]thieno[2,3-b]-pyridines through electrocyclization (and eventual dehydrogenation) of the initial aza Wittig imine products.