4j Radical cations of tetrasubstituted alkenes absorb at I,,,, i i 280 nm: P. S. Williams, B. C. Gilbert, R. 0. C. Norman: 3rd Int. Symp. Org. Free Radicals, Poster No. M 21, Freiburg 1981. IS] In unpolar solvents (room temperature) aromatic radical anions release an electron with high quantum yields even upon long wavelength irradiation: U. Sowada, R. A. Holroyd, J. Phys. Chem. 85 (1981) 541. Substituted cyclopropenyldiazomethanespotential precursors of tetrahedraneshave been studied many times. So far, it is not known how a cyclopropenylcarbene behaves in argon at 10 K. In order to reduce the synthetic difficulties we have chosen the trimethylsilyl analogues, in the hope that the protecting groups could be removed at the end of the synthetic sequence[41.The CuBr-catalyzed thermolysis of methyl diazoacetate in presence of bis(trimethylsilyl)acetylene 1 affords the cyclopropenecarboxylic acid ester 2at6! Reduction with diisobutylaluminium hydride leads to alcohol 2b and subsequent oxidation with silver carbonate/celite to aldehyde 2c. Condensation with tosylhydrazide smoothly yields tosylhydrazone 2d (Table I), which reacts with butyllithium to furnish salt 2e. SiMe, H I Me3Si/ SiMes 2a, R = C0,Me; Zb, R = CH,OH; Zc, R = CHO; 2d, R = CH=N-NHTos; Ze, R = CH=N-NLiTos; Zf, R = CHN, Table I. (Selection) 2a-2d : Yields, physical and spectroscopic properties; 'H-NMR (CDCI.,; &values rel. to TMS). All substances gave correct elemental analyses.