Quest for Even Higher Stabilized Foiled Carbenes

Abstract

Foiled carbene structures comprising strong stabilizing interactions between the divalent carbon and the intramolecular double bond have been located by DFT calculations. These tetracyclic species bearing fused five-membered rings impeding intramolecular rearrangements are theoretically predicted to lie in a deep potential energy well. A suitable dibromocyclopropane precursor for this type of foiled carbene has been prepared in 12 steps. Its treatment with methyllithium led to the isolation of a product of a formal carbene dimerization, a bicyclopropylidene.

Pentacycloundecanylidene and pentacycloundecanone – hyperconjugatively stabilized carbene and ketone

“…are reported experimentally or computationally. [11][12][13][14][15][16][17] They are normally classified in the category of foiled carbenes. 18,19 The stability of these carbenes was explained by through-space interaction, non-classical bonding and hyperconjugative interaction.…”

Intermolecular Reactions of a Foiled Carbene with Carbonyl Compounds: The Effects of Trishomocyclopropyl Stabilization

“…[18][19][20] Computational chemistry is an indispensable method to study shortlived reaction intermediates. 21 It has provided insight into the nature of foiled carbenes, [22][23][24] such 4 as endo-tricyclo[3.2.1.0 2,4 ]oct-8-ylidene (1) (Figure 2a) [25][26][27][28] and bicyclo[2.2.1]hept-2-en-7-ylidene (2) (Figure 2b). 29,30 Intramolecular carbene cycloaddition is foiled because the product would be greatly strained by its inverted C atom.…”

“…“Foiled reaction” carbenes were conceived as an approach toward stabilizing the closed-shell S 1 (n,p) state of a carbene to the point that it would supersede the T 0 (n,p) state, thus becoming the ground electronic state. − Computational chemistry is an indispensable method to study short-lived reaction intermediates . It has provided insight into the nature of foiled carbenes, − such as endo -tricyclo­[3.2.1.0 2,4 ]­oct-8-ylidene ( 1 ) (Figure a) − and bicyclo[2.2.1]­hept-2-en-7-ylidene ( 2 ) (Figure b). , Intramolecular carbene cycloaddition is foiled because the product would be greatly strained by its inverted C atom . Instead, an in-between structure is adopted.…”