Force field-SCF calculations on cyclopropene intermediates in carbene rearrangements. Comparison with experiment

Azulenylcarbenes: Rearrangements on the C11H8 Potential Energy Surface

“…reported that the thermolysis of the naphthylcarbene precursors 26 and 27 at 600 °C yields 7 as major product in addition to small amounts of 18 . The authors propose a mechanism via indenylcarbene 23 , which is formed in multiple steps from naphthylcarbenes 1 and 2 (Scheme ) . Hydrocarbon 18 is thus a common product of the rearrangements of the naphthylcarbenes 1 and 2 and of 1‐azulenylcarbene 9 .…”

“… Thermolysis of the naphthylcarbene precursors 26 or 27 yields high amounts of cyclobuta[ de ]naphthalene 7 as well as small amounts of cyclopenta[ cd ]indene 18 . Thermolysis of the precursor of 1‐azulenylcarbene 9 also yields 7 and 18 .…”

“…[22,24] Wentrup et al reportedt hat the thermolysis of the naphthylcarbene precursors 26 and 27 at 600 8Cy ields 7 as major product in addition to smalla mounts of 18.T he authors propose am echanism via indenylcarbene 23,w hich is formed in multiple steps from naphthylcarbenes 1 and 2 (Scheme5). [25] Hydrocarbon 18 is thusacommon product of the rearrangements of the naphthylcarbenes 1 and 2 and of 1-azulenylcarbene 9.I nterestingly,t he pyrolysis of azulenyldiazomethane 10 also produces 7,w hich suggests that 1-azulenylcarbene 9 and 1-naphthylcarbene 1 interconverta th igh temperatures. [23] Ar easonable mechanism of this interconversion involves ring expan-sion of azulenylcarbene 9 to carbene 16,a so bserved photochemically under conditions of matrix isolation, which through hydrogen shiftm ight give carbene 5.F rom there, rearrangement to cyclopropene 3 could provide the entry to the naphthylcarbene potential energy surface (Scheme 5).…”

“…Scheme5.Thermolysis of the naphthylcarbene precursors 26 or 27 [25] yields high amountso fc yclobuta[de]naphthalene 7 as well as small amountsofc yclopenta[cd]indene 18.Thermolysis of the precursor of 1-azulenylcarbene 9 also yields 7 and 18. [23] Relative energies in kcal mol À1 were calculated at (U)B3LYP/6-311 + G(d,p)l evel of theory.…”

Matrix isolation and photochemistry of 1- and 2-naphthylchlorocarbene

“…Thus, the naphthyl systems behave quite differently than phenylcarbene 1, which readily ringexpands to cycloheptatetraene 3 on light absorption. It is tempting to speculate on the origin of this dichotomy, following the lead of Wentrup et al 25 and Xie et al, 24 on the parent naphthylcarbene potential energy surface. Simple-mindedly, although electrocyclic ring-opening of the parent bicycloheptatriene 2 to the cycloheptatraene 3 is energetically very favorable, rearrangements of the cyclopropenes 13 and 18 to the corresponding allenes 15 and 20 are predicted to be endothermic.…”