Tautomerism-Dependent Ring Construction of N-Heterocyclic Compounds from the Reactions of 1-Alkynyl Fischer CarbeneComplexes and Substituted Pyrazolinones

摘要

Four types of N-heterocyclic ring systems were successfully constructed from the reactions of 1-alkynyl Fischer carbene complexes (OC)_5M=C(OEt)C=CPh (1)(M =Cr,W)and substituted pyrazolinones (2).Reactions of 1 with 3-methyl-2-pyrazolin-5-one (2a),3-n-propyl-2-pyrazolin-5-one (2b),3,4-dimethyl-2-pyrazolin-5-one (2c),3,4-trimethylene-2-pyrazolin-5-one (2d),or 3,4-tetramethylene-2-pyrazolin-5-one (2e)generated three kinds of Fischer aminocarbene complexes (3-5),and reactions of 1 with phenyl-substituted pyrazolinones,i.e.,3-phenyl-2-pyrazolin-5-one (2f)and its tautomer 3-phenyl-3-pyrazolin-5-one (2g),gave Fischer alkoxycarbene complexes (6)as the major products and aminocarbene complexes of types 3-5 as the minor products.Multiple tautomerism of pyrazolinones is attributed to the versatile formation of N-heterocyclic Fischer carbene complexes.Oxidative demetalation of complexes 3-6 with pyridine N-oxide or m-chloroperoxybenzoic acid efficiently afforded organic carbonyl products,and thus,strongly fluorescent syn-mixed-bimanes were prepared.The present findings constitute an alternative new method to synthesize mixed bimanes and other novel N-heterocyclic compounds.