Dialkyl triketones

The venomous constituent of the cryptic thief ant, Solenopsis xenovenenum, has been identified as the 3-heptyl-5-methylpyrrolizidine (50) from its mass spectrum and the fact that a related pyrrolidine (51) has been isolated from another species of ant.47 This is the first reported occurrence of a 3,5-dialkyl-pyrrolizidine, and its structure was confirmed by synthesis. Reductive amination of the known triketone (52) with sodium cyanoborohydride and ammonium acetate gave a mixture of four isomers of 3-heptyl-5-methylpyrrolizidine, which were separated by preparative g.l.c. The stereochemistry of the ring-junction of each isomer was established from its i.r. and n.m.r. spectra. 

Diaryl triketones do not show the same reactivity as their dialkyl counterparts. This is illustrated by the fact that 19-hr irradiation through Pyrex using the full spectrum of a 1000-W, high-pressure, mercury-vapor lamp was required for 90% disappearance of 250 mg of diphenyl triketone (13) in degassed p-xylene solution. The major products isolated were p,p -dimethylbibenzyl, benzaldehyde, and p-methyl-benzyl phenyl ketone in addition, minor amounts of oxidation products such as p-methylbenzyl benzoate were identified, as well as traces of benzil. Quantum yields for the disappearance of 13 at 436 nm in degassed or air-saturated p-xylene solutions were about 3 x 10 k nearly identical values were obtained... 

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