Isomerisation of 1- and 2-naphthylcarbene to cyclobuta[de]naphthalene

Azulenylcarbenes: Rearrangements on the C11H8 Potential Energy Surface

“…The three new azulenylcarbenes 12, 14,a nd 15 with the carbene centers attached to positions 2, 5, and 6o ft he azulene system,r espectively,s how triplet ground states,w hereas the previously known 9 with the carbene center in 1-position is as inglet ground state carbene. The S-T splittingso ft he azulenylcarbenes roughly parallel the p-electron densities at the various positions in the azulener ings, which were estimated from 13 Co r 1 Hc hemical shifts or from quantum chemicalc alculations ( Figure 5). [30] High electron densities stabilize the singlet states more than the triplets, and thusr educe the S-T splitting of the triplet carbenes or even result in as inglet ground state.…”

“…The primary products of the rearrangements of 1 and 2 are the highly strained cyclopropenes 3 [10] and 4, [11] respectively,w hich are furthermore formed by rearrangement of the benzocycloheptatrienylidenes 5 and 6. [12] Flash vacuum pyrolysis established an isomerizationp athway between carbenes 1 and 2,u ltimately producing cyclobuta-[de]naphthalene (7) [13] by insertion of the carbene center of 1 into aC ÀHb ond in the naphthalene peri position. Benzocycloheptatetraene (8)w as identified as intermediate in the carbene-carbene rearrangement of 1 to 2.…”

Six Low-Lying Isomers of C11H8 Are Unidentified in the Laboratory–A Theoretical Study

“…Isomer 3 has been prepared from 1- and 2-naphthylcarbenes or its derivatives through thermal rearrangements. , Wentrup and co-workers synthesized 3 from 1-azulenylcarbene using falling solid flash vacuum pyrolysis (FS-FVP) . Another route to the syntheses of 3 and its derivatives has been achieved by vacuum thermolyses of [methoxy­(trimethylsilyl)­methyl]­naphthalenes. , Synthesis and characterization of isomer 1 have been documented elsewhere by several research groups. − ,,, Isomers 4 and 5 , , that energetically lie 50 and 53 kJ mol –1 above 1 , respectively, at the fc-CCSD­(T)/cc-pVTZ//fc-CCSD­(T)/cc-pVDZ level have also been synthetically characterized. Within 1 H -indene system, isomers 6 , 7 , 8 , and 9 that lie 54, 54, 56, and 57 kJ mol –1 above 1 , respectively, at the former level remain elusive till date.…”

“…11 Another route to the syntheses of 3 and its derivatives has been achieved by vacuum thermolyses of [methoxy(trimethylsilyl)methyl]naphthalenes. 24,25 Synthesis and characterization of isomer 1 have been documented elsewhere by several research groups. [1][2][3]11,12,88 Isomers 4 27 and 5, 28,29 that energetically lie 50 and 53 kJ mol −1 above 1, respectively, at the fc-CCSD(T)/ cc-pVTZ//fc-CCSD(T)/cc-pVDZ level have also been synthetically characterized.…”

“…The most stable isomer, 1 H -cyclopenta­[ cd ]­indene ( 1 ; see Figure ) was isolated by different groups in the early 1970s. , Wentrup and co-workers synthesized 1 by flash vacuum pyrolysis of 1-(2-diazoethylidene)­indene at 600 °C. Another experimentally well-known low-lying isomer for C 11 H 8 is cyclobuta­[ de ]­naphthalene ( 3 ). ,,,,− For a long time, 3 has been considered as the global minimum isomer , on the potential energy surface of C 11 H 8 instead of 1 . ,,, Within 1 H -indene system, 2-ethynyl-1 H -indene ( 4 ) and 3-ethynyl-1 H -indene ( 5 ) , have been synthetically characterized in the past but only recently, using synchrotron-based vacuum ultraviolet ionization mass spectrometry, 1-ethynyl-1 H -indene ( 11 ; see Figure ) has been detected by Kaiser and co-workers . A bimolecular reaction between the 1-indenyl (C 9 H 7 •) radical and acetylene (C 2 H 2 ) has been carried out at 150 0 ± 10 K and 300 Torr pressure.…”