In the 1920s, this chemist and Leopold Ružička (“roo-ZHEECH-kah”) elucidated the molecular structures normally derived from Chrysanthemum cinerariifolium to aid development of pyrethroid insecticides. One reaction named for this chemist can be classified by whether it can form an amide bond without incorporating residual atoms, leading it to be called “traceless.” (15[1])This chemist names a reaction that, via a non-photochemical 2-plus-2 (15[1])cycloaddition, forms (*) beta-lactam antibiotics by reacting (10[1])an imine with a compound whose (-5[1])simplest member is ethenone. This chemist is the namesake of a reaction that can start with a phosphine or phosphite to form an imino·phosphor·ane, and specifically can reduce an azide to an amine; that reaction is important in bioconjugation (-5[1])methods in its so-called “ligation” (10[2])form. For 10 points, name this German organic chemist known for his discovery of ketenes. ■END■ (10[2]0[4])