Bicyclo pent

The recent upsurge of interest in systems of theoretical interest demands practical syntheses of several important compounds. These are BICYCLO[2.l.0]PENT-2-ENE, BENZOCYCLOPROPENE, 1,6-OXIDO[10]ANNULENE, and others. ewdo-TRICYCLO[4.4.0.02 5]-DECA-3,8-DIENE-7,10-DIONE is utilized as a model for the use of CYCLOBUTADIENE IN SYNTHESIS, and a stable monomeric ketene, icri-BUTYLCYANOKETENE offers opportunities for further studies of this interesting species. 

Summing up these results, it has been shown that the carbene bridgehead olefin-carbene rearrangement is also observed when diazoalkanes are the precursors for the generation of the bicyclo[l.l.l]pent-l-ylcarbenes of type 52. 

C2O-C3O l,4-Dioxa-spiro[2.3]hexane 2, 371 5-Thia-bicyclo[2.1.0]pent-2-ene 1, 398... 

Azatricyclo[2.2.1.02 6]hept-7-yl perchlorate, 2368 f Azetidine, 1255 Benzvalene, 2289 Bicyclo[2.1.0]pent-2-ene, 1856 2-/ert-Butyl-3-phenyloxaziridine, 3406 3 -Chloro-1,3 -diphenyleyclopropene, 3679 l-Chloro-2,3-di(2-thienyl)cyclopropenium perchlorate, 3388 Cyanocyclopropane, 1463 f Cyclopropane, 1197 f Cyclopropyl methyl ether, 1608 2,3 5,6-Dibenzobicyclo[3.3.0]hexane, 3633 3,5 -Dibromo-7-bromomethy lene-7,7a-dihy dro-1,1 -dimethyl-1H-azirino[l,2-a]indole, 3474 2.2 -Di-tert-butyl-3.3 -bioxaziridinc, 3359 Dicyclopropyldiazomethane, 2824 l,4-Dihydrodicyclopropa[ >, g]naphthalene, 3452 iV-Dimethylethyl-3,3-dinitroazetidine, 2848 Dinitrogen pentaoxide, Strained ring heterocycles, 4748 f 1,2-Epoxybutane, 1609 f Ethyl cyclopropanecarboxylate, 2437 2,2 -(l,2-Ethylenebis)3-phenyloxaziridine, 3707 f Methylcyclopropane, 1581 f Methyl cyclopropanecarboxylate, 1917 f Oxetane, 1222... 

V1ethoxycarbonyl)ethyl]bicyclo[l.l.l]pent-1-yl -4,5-dihyilrofuran-2(3//)-oiic (27) Typical Procedure 43... 

The photoisomerization of 2-(pent-4-enyl)-3-oxycyclohex-2-enones 5 to 6-oxytricyclo[6.3.0.01,6]-undecan-2-ones 6 has been used as a key step for the synthesis of sesquiterpenes containing the bicyclo[6.3.0]undecane carbon skeleton.15 16... 

Bicyclo[3.1.0]hex-2-ene, 291 sigmatropic rearrangement, 290-291 Bicyclo[2.1.0]pent-2-ene, 289 Bishomocyclopropenyl cation, 277 Bond, definition of, 50 Bond angles... 

Bis-[trifluoioinet iyl)-1,7-dimethyl- E10b2. 277 (Rj-5-thia-bicyclo[2.1.0]pent-2-enc +... 

Alternatively, we can deduce some homoaromatic stabilization of bicyclo[4.1.0]hepta-2,4-diene and homo antiaromatic destabilization of bicyclo[2.1.0]pent-2-ene from enthalpies associated with hydrogenation to form the saturated bicycloalkanes. The bicy-cloheptadiene hydrogenation enthalpy (i.e. 39 —> 18, n = 6) is ca 200 kJ mol-1, to be compared with (229.6 1.3) kJ mol1 for the hydrogenation of the corresponding monocyclic... 

Equation 37 and the accompanying analysis documents that cyclobutane is essentially normal, i.e. cyclobutene and cyclobutane are not particularly different in terms of their strain energy. One might therefore expect that the enthalpy of formation difference of bicy-clo[2.1.0]pentane (17) and bicyclo[2.2.0]hexane (54) of 34.0 kJ mol1 (the above n = 2 case) would approximately equal that of the unsaturated bicyclo[2.1,0]pent-2-ene (41) and bicy-clo[2.2.0]hex-2-ene (55). However, the difference is ca 83 kJmoT1 for the latter pair101. The... 

We hesitate to use a proof by existence to document our assertion—that is, bicyclo[2.1.0]pent-2-ene is isolable under conventional chemical conditions while cyclobutadiene is not. As such, our analysis (derived from that of Jorgensen67 ) must use quantum chemical calculations whenever the thermochemistry of cyclobutadiene is needed. 

The addition of a hydrogen atom to la to yield the bicyclo[l. 1.1 ]pent-1 -yl radical (6) has been calculated (UHF/MP2 6-31G ) to be exothermic by only 47 kcalmol"1 19. The addition of the second hydrogen atom to the radical to form bicyclo[l.l.l]pentane was calculated (MP3 6-311G ) to be exothermic by 104.4 kcalmol"143 (equation 4). By this argument, the strength of the central bond in la is about 60 kcalmol"1319 and is comparable to that in cyclopropane. 

Bicyclo[l. 1. l]pent-1 -yl anions (13) and radicals (14) carrying a suitable leaving group in position 3 undergo a 1,3-elimination reaction (path/, an intramolecular analog of Sw2 and S 2 substitution, respectively) and yield [l.l.ljpropellane (equations 6 and 7 Table 10). 

Before proceeding to a discussion of the reactions of the central bond of [1.1.1] propellane, it will be useful to describe the properties of the first-formed intermediates, the bicyclo[l, l.l]pent-l-yl anion 16, radical 6, and cation 19. 

Radical attack on the central bond in [1.1.1 [propellane 1 occurs 2-3 times faster than attack on styrene96 and yields bridgehead bicyclo[l.l.l]pent-l-yl radicals6. Laser flash photolysis techniques were used to measure the rate constants for the reactions of la with five different radicals (Table 12)96"99. The addition of the phenylthiyl radical to la is... 

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