Born Jan. 14, 1851, in Cologne; died Jan. 5, 1930, in Bad Godesberg. German organic chemist. Professor at the universities of Kiel (from 1897) and Berlin (from 1904).
Claisen achieved a number of organic syntheses, including the synthesis of isatin. In 1887 he studied the condensation reaction that is named after him (seeCLAISEN CONDENSATION). From 1900 to 1905 he studied the tautomeric conversions of acetoacetic ester (ethyl acetoacetate). In 1912 he discovered the rearrangement of allyl ethers of phenols into corresponding allyl-substituted phenols (seeCLAISEN REARRANGEMENT).