The structure of the Cycloaddition products of C-(2-thenoyl)-N-arylmethanohydrazonyl bromides to some substituted olefins

The cycloaddition of C‐(2‐thenoyl)‐N‐arylnitrilimines 2a, b to acrylic acid derivatives 3‐5, fumaric acid derivatives 9‐10, benzalmalononitrile 14 and N‐arylmaleimides 20 has been studied. Under thermal conditions these 1,3‐dipolar cycloadditions proceed with absolute regio‐chemistry to yield 5‐substituted‐2‐pyrazolines 6‐8, 11‐12, 16 and 21, respectively. The cycloadducts 11 and 16 lose hydrogen cyanide to give the corresponding pyrazoles 13 and 18, respectively.