Such an imine-mediated mechanism was first proposed by Paul Rumpf (1908–1999) in 1935,[5] and experimental evidence was provided by Hardonk and van Duijn in 1964.[6] In 1980, Robins, Abrams and Pincock provided substantial NMR evidence for the mechanism, leading to its general acceptance.[7] Stoward had examined the mechanism in 1966 and, on the whole, considered this mechanism to be correct.[8]