16764-72-0Relevant articles and documents
Competitive 1,2-C Atom Shifts in the Strained Carbene Spiro[3.3]hept-1-ylidene Explained by Distinct Ring-Puckered Conformers
Rosenberg, Murray G.,Schrievers, Theodor,Brinker, Udo H.
, p. 12388 - 12400 (2016/12/23)
Spiro[3.3]hept-1-ylidene is a markedly strained carbene reaction intermediate that was generated by high-vacuum flash pyrolysis (HVFP) of the corresponding p-tosylhydrazone sodium salt. Five hydrocarbons were produced from the Bamford-Stevens reactant in 82% overall yield. The carbene undergoes two [1,2]-sigmatropic rearrangements via competing 1,2-C atom shifts. Ring-contraction yields cyclopropylidenecyclobutane, while ring-expansion affords bicyclo[3.2.0]hept-1(5)-ene. The ring contraction is regiospecific despite the formation of some 1-methylenespiro[2.3]hexane. It does not originate from the carbene under HVFP conditions. Instead, it comes from a methylenecyclopropane-type rearrangement of chemically activated cyclopropylidenecyclobutane. Similarly, some chemically activated bicyclo[3.2.0]hept-1(5)-ene rearranges to 1,2-dimethylenecyclopentane via electrocyclic ring-opening. Accounting for the conversion of primary products to secondary ones, relative yields indicate that ring-contraction within the carbene prevails over ring-expansion by a factor of 6.7:1. Computational chemistry was used to assess the structures, conformations, energies, strain energies, transition states, and activation energies of these rearrangements with the goal of explaining product selectivities. The dual-ringed carbene is predicted to assume four distinct geometric conformations that have a bearing on transition-state selection. The reactive cyclobutylidene units of two conformers are significantly puckered, like cyclobutylidene itself, while those of the other two are flatter. The selectivity of the title carbene is compared with that of spiro[2.3]hex-4-ylidene.
Polylithiumorganic compounds -19. Regioselective carbon-carbon σ-bond scission followed by a 1,6-proton shift upon the reductive metalation of benzylidenecyclopropane derivatives with lithium metal
Maercker, Adalbert,Daub, Volker E. E.
, p. 2439 - 2458 (2007/10/02)
Depending on the substituent α-substituted benzylidenecyclopropanes (32) react more or less readily with lithium dust (2% sodium) in diethyl ether whereby a regioselective scission of only the cyclopropane σ-bond cis to the phenyl ring takes place. Upon raising the temperature the primarily formed 1,3-dilithiumorganic compound due to an agostic interaction rearranges by a 1,6-proton shift into a doubly bridged 1,4-dilithio compound. With α-methylbenzylidenecyclopropane (32c) this rearrangement was shown to occur intermolecularly via a trilithiumorganic compound 56. The suggested mechanism of these reductive metalation reactions via a bisected radical anion 87 where the lithium is mainly bound to the cyclopropyl carbon atom and oriented syn to the phenyl ring, was supported by MNDO (geometries) and ab initio (energies) calculations.
The chemistry of small-ring compounds. Part 47. Small-ring interference in the ozonolysis of cyclopropylidenecycloalkanes
Heuvel, C. J. M. van den,Hofland, A.,Velzen, J. C. van,Steinberg, H.,Boer, Th. J. de
, p. 233 - 240 (2007/10/02)
Ozonolysis of olefins Ia-c containing a cyclpropylidene group, does not follow the classical Criegee mechanism but gives the anomalous products IIa-c, IIIa-c, IVa-c, and Va-c, as outlined in Scheme 2.None of these oxidation products contains the cycloprop
