Decomposition of 4,6-dimethylbenzocyclobutenone p-toluenesulfonylhydrazone

Chemistry of Conversions of [o-[1-Halo-1-(p-tolylsulfonyl)alkyl]benzyl]trimethylsilanes to o-Quinodimethanes and Benzocyclobutenes

“…Of particular interest is that α-alkyl-α-bromosulfones 19a − f are converted by TBAF in acetonitrile at 20−25 °C to benzocyclobutenes 21a − f (eq 7) and vinyl sulfones 23a − f (eq 8) as summarized in Table . , Other than for 21a , benzocyclobutenes 21b − f are the major products (49−61% yields); vinyl sulfones 23b − f are formed in 15− 22% yields. The benzocyclobutenes give acceptable analyses and expected MS data.…”

The Elusive Benzocyclobutenylidene: A Combined Computational and Experimental Attempt

“…( (22) One may ponder whether vinylidene 2 or cycloalkyne 3 play any role in the condensed phase experiments. [4][5][6] Vinylidene 2, if formed, may be expected to undergo rapid thermal isomerization to benzocyclobutenylidene 1 1sthe intermediate that has been presumed to be responsible for the solution phase chemistry. It is also intriguing to note that vinylidene 2 is computed to be isoenergetic with triplet benzocyclobutenylidene 3 1.…”

“…Several groups attempted to study carbene 1 or its simple derivatives by photolysis or thermolysis of various precursors. − Product analyses revealed a complex and intriguing reactivity for 1 but did not provide a clear conclusion as to the multiplicity of the ground state. Semiempirical calculations suggested a triplet ground state .…”

Cyclobutenylidene: A Multifaceted Two-Coordinate Carbon Species Obtained via Skeletal Editing of a Cyclopropenylidene

“…13−15 While the lower homologue of cyclobutenylidene, cyclopropenylidene (CPD) 16 is abundant in interstellar medium and Titan 17−19 due to the stabilization brought by the partial 2π aromaticity, CBY is known to be extremely unstable due to insufficient electronic stabilization of the carbenic center as well as its high tendency to isomerize into more stable acyclic isomers with strain release. 2,3,13−15 The synthetic trials of CBYs date back to 1969 reported by Heins and Blomquist, 20 but not until 2001 have Tomioka and co-workers reported the first observation of a UV−Vis absorption signal (λ max = 450 nm) possibly assignable to the benzocyclobutenylidene which was generated upon laserflash photolysis of the corresponding oxadiazoline precursor. 14 CBY-transition metal complexes have also been sought as intermediates for metathesis reactions; 21,22 however, no free CBY has been synthesized as a persistent or isolable species up to date.…”

“…One of the elusive C 4 H 4 -isomers, cyclobutenylidene (CBY), is predicted to exhibit a puckered geometry different from all other cycloalkenylidenes (Figure b). − Such geometric features of CBY have attracted considerable interest of organic and physical chemists and casted debate whether there is a C–C bond running across the center of the ring, which should give CBY a resonance contribution of a bicyclo[1.1.0]­but-1(2)-ene, the smallest bridgehead olefin (Figure b). − While the lower homologue of cyclobutenylidene, cyclopropenylidene (CPD) is abundant in interstellar medium and Titan − due to the stabilization brought by the partial 2π aromaticity, CBY is known to be extremely unstable due to insufficient electronic stabilization of the carbenic center as well as its high tendency to isomerize into more stable acyclic isomers with strain release. ,,− The synthetic trials of CBYs date back to 1969 reported by Heins and Blomquist, but not until 2001 have Tomioka and co-workers reported the first observation of a UV–Vis absorption signal (λ max = 450 nm) possibly assignable to the benzocyclobutenylidene which was generated upon laser-flash photolysis of the corresponding oxadiazoline precursor . CBY-transition metal complexes have also been sought as intermediates for metathesis reactions; , however, no free CBY has been synthesized as a persistent or isolable species up to date.…”