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Efficient Iminophosphorane‐Mediated Preparation of Benzofuro[3,2‐ d ]pyrimidin‐4(3 H )‐ones and Unexpected Ring Opening Products
Author(s) -
Hu YangGen,
Liu MingGuo,
Ding MingWu
Publication year - 2008
Publication title -
helvetica chimica acta
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.74
H-Index - 82
eISSN - 1522-2675
pISSN - 0018-019X
DOI - 10.1002/hlca.200890090
Subject(s) - chemistry , ring (chemistry) , structural isomer , alkoxide , guanidine , catalysis , medicinal chemistry , primary (astronomy) , base (topology) , stereochemistry , organic chemistry , mathematical analysis , physics , mathematics , astronomy
The carbodiimides 4 , obtained from aza‐ Wittig reactions of iminophosphorane 3 with aromatic isocyanates, reacted with secondary amines, phenols or alcohols in the presence of catalytic amounts of K 2 CO 3 or sodium alkoxide to give 2‐substituted benzofuro[3,2‐ d ]pyrimidin‐4(3 H )‐ones 6 . However, when 2,2′‐iminobis[ethanol] was used, the unexpected ring opening product 7 was formed instead of 6 . Reaction of 4 with primary amines RNH 2 (R=Et, Pr, Bu, etc. ) gave guanidine intermediates 8 , which were further treated with EtONa to give only one regioisomer 9 via a base catalyzed cyclization. However, another regioisomer 11 was obtained when NH 3 or ‘small’ amines RNH 2 (R=Me, NH 2 ) were used in the absence of EtONa via a spontaneous cyclization of 8 .