Bicyclo hept-2-enes rearrangement

Bicyclo[3,2,0]heptane and Bicyclo[4,2,0]octane Derivatives.—The bridged bicyclo-[l,l,0]butanes (281), (282), and (283) rearrange thermally to the bicyclo[3,2,0]hept-enes (284) and (285). The rates of rearrangement are most rapid where radical stabilization by bridging functionality is possible, i.e. (283) reacts more rapidly than (282) which is in turn more reactive than (281). Use of substrates with deuterium specifically incorporated at the 6- and 7-positions showed that these positions become the olefinic positions in the newly formed cyclobutene ring. 

Very highly constrained bicyclic alkenes rearrange via carbene intermediates to ring-contracted products. Thus, bicyclo[3.3.0]oct-2-ene gave 6-methylenebicyclo[3.2.0]heptane (38), and bicy-clo[2.2.1]hept-2-ene gave 5-methylenebicyclo[2.1.1]hexane (39).113... 

Several photochemically induced vinylcyclopropane to cyclopentene rearrangements of nor-carene derivatives to form bicyclo[3.2.0]heptenes can be understood as ring contractions of cyclohexenes to cyclobutanes. Upon direct irradiation of norcar-2-ene (bicyclo[4.1.0]hept-2-ene) at 214 nm (pentane solution), however, complex product mixtures were obtained containing only small amounts of bicyclo[3.2.0]hept-2-ene, while toluene sensitized photolysis in 50 millimolar solution in degassed pentane at 254 nm gave mainly the cyclobutane derivative 13 in addition to EjZ-isomeric hepla-l,3,6-trienes.72... 

Apart from the rearrangement of the tricyclo[4.1.0.03/7]heptane to the bicyclo[2.2.1]hept-2-ene system under acid catalysis, it can be effected by silver(I) perchlorate [silver(I) assisted ionization]19 and by photolysis at 185 nm.20... 

Me3Si)2S in the presence of Me3SiOTf induces the rearrangement of bis[(Mes)metha-noyl] bicyclo[2.2.1]hept-5-enes to 2-oxabicyclo[3.3.0]octa-3,7-dienes (equation 20)38. 

A TBAF-induced elimination/rearrangement of certain 4- /t-butyldimethylsilyloxy-2-amino-l-aza-bicyclo[4.1.0]-hept-3-enes led to substituted l//-azepin-4(7//)-one derivatives in low to fair yields rearrangement to N-substituted pyrid-(177)-ones was a substituent-dependent competing process <2007T11167>. 

Some ester- or aldehyde-substituted bicyclo[2.2.2]oct-2-ene and bicyclo[2.2.1]hept-2-ene systems (25) have been shown to undergo nitrosation adjacent to the carbonyl group followed by [3,3]-sigmatropic rearrangement to give oxazine products (26).23 Stereodeflned monoprotected allylic 1,2-diol (27) and its diastereomer have been ( ) converted into stereodeflned propenylimidazolidinone (30) and its diastereomer by... 

Endo-skeletal rearrangements also take place with 1,6-enynes, bnt the proposed mechanism is just a variation of the exo-single-cleavage rearrangement. Formed by endo cyclization, bicyclo[4.1.0]hept-4-ene derivatives arise in some cyclizations of 1,6-enynes by proton loss and protodemetalation ofthe endo cyclopropylcarbene. " That is the case from 1,6-enynes tethered as sulfonamides and in the intramolecular cyclization of 1,6-enol ethers with alkynes (equation 40). ... 

Also related to pathway b, Hodgson et al. were able to obtain 2-aza-bicyclo[2.2.1]hept-5-enes from 7-azabicyclo[2.2.1]heptadienes by a tandem featuring a thiyl intermolecular addition followed by a homoallylic radical rearrangement [92]. 

Although relatively little work has been done in this area, Schneider and Csacsko have shown that 7-endo-vinylbicyclo[4.1.0]hept-2-ene (182) rearranges to bicyclo[3.2.2]nona-2,6-diene (183) under conditions (< 25 C) similar to those required for tend reorganization of ci5-l,2-divinylcyclopropane or... 

Although small in number, the investigations summarized above show that the Cope rearrangement of 7-(l-alkenyl)bicyclo[4.1.0]hept-2-enes is an effective method for the synthesis of usefully functionalized bicyclo[3.2.2]nona-2,6-dienes. 

In contrast to acyclic 1,4-dienes, which rearrange to vinylcyclopropanes from the excited singlet state vide supra), cyclic 1,4-dienes usually undergo the di-7i-methane rearrangement from the triplet state.Bicyclo[3.1.0]hex-2-enes (2, n = 1) and bicyclo[4.1.0]hept-2-enes (2, n = 2) are thus obtained from eyelohexa-1,4-dienes and eyclohepta-1,4-dienes, respectively. 

In a mechanistically similar rearrangement, norborn-5-ene- and bicyclo[2.2.2]oct-5-ene-2-boronic acid under the conditions of mercurio deboronation yield tricyclo[2.2.1.0 ]hept-3-yl-and tricyclo[2.2.2.0 ]oct-3-ylmercury chloride, respectively.This corresponds to cyclopropane formation by homoallyl rearrangement (see Section 2.1.). For example, formation of 17 from 16. 

A Skattebol-type rearrangement of a l-bromo-l-(trimethylstannyl)cyclopropane derivative has been reported in which a dialkenylcyclopropane was formed. Thus, the endo-isomer of 7-bromo-7-(trimethylstannyl)bicyclo[4.1.0]hept-2-ene (1), when heated in benzene, gave bromotrimethyl-... 

It is noteworthy that irradiation of tetracyclo[6.2.0.0 . 0 ]decan-9-one resulted in cycloreversion and formation of ketene and vinylcyclopropane tricyclo[5.1.0.0 ]oct-5-ene instead of ring cleavage and decarbonylation. A C-C double bond a to a cyclopropane ring also resulted when spiro bicyclo[2.2.1]hept-5-ene-7,l -cyclopropane -2-one eni/o-epoxide underwent a deep-seated rearrangement upon irradiation through Corex to give 5-oxo-spiro[2.4]hept-6-ene-4-ylacetaldehyde in 50% yield. ... 

Reactions involving both Ca, C/i, and Cy relative to a cyclopropane ring can formally be classified as ene reactions, 1,3-sigmatropic rearrangements, and Sn2 substitutions. An ene reaction occurred on reaction of A-sulfinylbenzenesulfonamide with bicyclo[4.1.0]hept-3-ene 1 under mild conditions to give 2 in good yield. " Terpene 1 underwent a similar reaction on treatment with acetic anhydride in the presence of zinc(II) chloride. Compound 2 is... 

Similar to thermochemical intermolecular [2n- -2a] cycloadditions, the intramolecular version is also clearly promoted by phenyl substituents at the ends of the reacting cyclopropane bond. With phenyl groups in positions 2 and 4 of 3,3-dimethyltricyclo[3.2.0.0 " ]hept-6-ene (23, = Ph), a 60% yield of the 2n + 2a] cycloaddition product 24 (R = R = Ph) was obtained. If one of the phenyl groups is replaced by a methyl group (23, R = Me R = Ph), the yield decreased to 9%, even at 154°C. With two methyl groups in positions 2 and 4 (23, R = R = Me), only rearrangement products (bicyclo[3.2.0]heptadienes and cyclohepta-trienes) were observed. ... 

Other base-catalyzed ring enlargements include the reductive rearrangement of diethyl-bicyclo[4.1.0]hept-3-ene-l,5-dicarboxylate to diethylcyclohept-5-ene-l,5-dicarboxylate promoted by lithium in liquid ammonia (Section 2.4.1.5.2.6.). 9-Vinyl- and 9-arylbarbaralan-9-ols [9-substituted tricyclo[3.3.1.0 ]nona-3,6-dien-9-ols] 18 undergo retro-Diels-Alder reactions to give cycloheptadiene derivatives 19 on treatment with potassium hydride and 18-crown-6 in tetrahydrofuran. ... 

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