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The Bradsher cycloaddition was first reported by C. K. Bradsher and T. W. G. Solomons in 1958.
References
C. K. Bradsher, T. W. G. Solomons (1958). "Acridizinium Ion Chemistry. II.1The Diels-Alder Reaction". J. Am. Chem. Soc. 80 (4): 933. doi:10.1021/ja01537a045.