Base-Induced Cyclisation of ortho-Substituted 2-Phenyloxazolines to Give 3-Aminobenzofurans and Related Heterocycles

Abstract

Treatment of ortho-benzyloxyphenyloxazolines with butyllithium and potassium tert-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.