Base-induced cyclisation of ortho-substituted 2-phenyloxazolines to give 3-aminobenzofurans and related heterocycles

Treatment of ortho-benzyloxyphenyloxazolines with butyllithium and potassium t-butoxide results in cyclisation with ring-opening of the oxazoline to give 2-aryl-3-aminobenzofurans. The reaction also occurs with the corresponding benzylthio- and benzylamino-compounds to give benzothiophenes and indoles, respectively. Use of an ortho-allyloxyphenyloxazoline gives the corresponding 2-vinylbenzofuran, while both α-methylbenzyloxy and benzylsulfonyl compounds form stable spirooxazolidine products. The X-ray structure of an aminobenzothiophene product has been determined