Synthesis and Chemistry of a Bicyclobutane-Bridged α-Diazo Ketone

Article abstract of DOI:10.1021/jo01310a016

The preparation and a number of reactions of the bicyclobutane-bridged α-diazo ketone 1 are reported. The 1,3-dipolar addition of 1 to activated unsaturated carbon-carbon bonds affords heterocyclics with an intact bicyclobutane ring system. This is exemplified by the reaction of 1 with enone 8 to give pyrazoline 9 which provides upon photolytically or thermally induced extrusion of nitrogen the bis(bicyclobutane)-substituted cyclopropane 16. Compound 16 isomerizes thermally to dihydrobenzofuran derivative 17, which is an example of a cyclopropyl ketone-dihydrofuran rearrangement. Also, some reactions of 1 involving loss of nitrogen were investigated.The transition-metal-catalyzed decomposition of 1 in methanol leads to mixtures of phenol 24 and 2,5-cyclohexadienone 25. The AgClO4-catalyzed decomposition of 1 in the presence of electron-rich alkenes affords aromatic adducts, arising from a (formal) 1,3-dipolar addition of the α-keto carbenoid species to the alkene, whereas the analogous reaction with Rh2(OAc)4 furnishes 47, resulting from (formal) dimerization of the α-keto carbenoid with incorporation of an oxygen atom. The reaction of 1 with tetrachloro-o-quinone leads to formation of 23 in which the bicyclobutane moiety has remained intact; on the other hand, treatment of 1 with o-dihydroxybenzene provides a mixture of the rearranged adducts 49 and 51. Finally, the preparation and some properties of bis(tosylhydrazone) 4 are described.