3,4-Diazabenzvalene, the azoalkane precursor to tetrahedrane. Synthesis and reactivity.

Excited State Aromaticity and Antiaromaticity: Opportunities for Photophysical and Photochemical Rationalizations

“…It is Scheme 18. Photochemical Formation of Cyclobutadiene Using Various Precursors Such as Compounds 106, 127,320−323 108, 326 109, 318 110, 327 111, 319,324,325 112, 328 113, 326,327 114, 332 115, 331 116, 330 117, 334 and 118 329 particularly noteworthy that one of the new π-bonds formed is part of the CBD ring. Precursor 114, on the other hand, is interesting as the Fe(CO) 3 fragment formed upon decomposition is not a stable molecule, and both the CBD and Fe(CO) 3 products were only detected as short-lived intermediates by kinetic mass spectrometry.…”

“…For instance, irradiation of 111 leads exclusively to the [2 + 2] cycloaddition dimer of CBD and 1,3dihydro-2-benzofuran (phthalan), 335 whereas photolysis of 117 gives an approximate 1:1 product distribution between the CBD dimer and pyridazine. 334 For photolysis of 115 it is concluded that CBD is the major product. 331 On the other hand, irradiation of 113 for eight hours in a matrix at cryogenic temperatures yields the CBD dimer as the exclusive product in a yield of just 9%.…”

“…Scheme 18. Photochemical Formation of Cyclobutadiene Using Various Precursors Such as Compounds 106, 127,320−323 108,326 109, 318 110,327 111,319,324,325 112,328 113,326,327 114,332 115,331 116,330 117,334 and 118329 and the Weakly Bound T-Shaped Acetylene Dimer Complex 119333 Chemical Reviews…”

Tetrahedrane—Dossier of an Unknown

“…While Eaton and Cole [5] as well as Paquette et al [6] succeeded in the synthesis of cubane [CH] 8 (1964) and dodecahedrane [CH] 20 (1982), respectively, tremendous efforts to prepare 1 [7][8][9][10][11][12][13][14] resulted only in the detection of the C 4 H 4 isomers (Scheme 1) methylenecyclopropene (2), cyclobutadiene (3), acetylene dimer ((4) 2 ), and vinylacetylene (5). On three occasions, [7, 8a, b] however, reaction products were proposed to be consistent with the intermediacy of 1.…”

“…Thus, the rearrangement of tetrahedrane to cyclobutadiene or two acetylenes is strongly unfavorable, as reactions to 6-8 are, since the corresponding reaction barriers are sizable, in marked contrast to previous lower-level predictions. [15,24] Although 1 is highly strained, [13,19,20,23,29,32] it is not reactive, and should, in principle, be isolable. This is even more intriguing in light of the fact that strain, measured as a net effect is generally underestimated because of the neglect of thermodynamically stabilizing factors.…”