Bicyclo hept-5-enes thermolysis

A practical synthesis of bicyclo[2.1.0]pentane (6) by thermolysis of 2,3-diazabicyclo[2.2.1]-hept-2-ene has been reported in detail.13 It has already been shown that the conversion of 2,3-diazabicyclo[2.2.1]hept-2-ene to bicyclo[2.1.0]pentane involves a diradical intermediate.14... 

This method of nitrogen elimination from tetrahydropyridazines is frequently used in the synthesis of polycyclic systems. The thermolysis, as well as photolysis, of 2,3-diazabicy-clo[2.2.1]hept-2-enes gave bicyclo[2.1.0]pentanes via intermediate formation of cyclopenta-1.3-diyl, from which bicyclic compounds with one three-membered and one four-membered segment are formed this type of reaction is discussed in Houben-Weyl, Vol. E17b, pp 1089-1108 and 1163-1166. 

The concerted nature of these reactions is also supported by the pyrolytic cleavage of cis-2,3-dimethylcyclobutanone and rra i-2,3-dimethylcyclobutanone at a temperature of 325 °C under a pressure of 10 Torr, from which approximately 99% retention of configuration in the resulting but-2-enes is observed.92,93 Moreover, the results obtained from the thermolysis of cis- and m -2,4-dimethylcyclobutanone also lend support to the concertedness of this reaction.92,93 However, as substantiated by Arrhenius parameters, a diradical pathway is the most likely competing reaction in the pyrolysis of 2-chlorocyclobutanone.94 On the other hand, the kinetics of the gas-phase pyrolysis of bicyclo[3.2.0]hept-2-en-6-one (14),95 bicyclo[3.2.0]heptan-6-one (IS)96 and 2,2-dimethyl-3-ethoxycyclobutanone (16)97 are commensurate with a concerted cycloreversion mechanism involving four-center auasi-zwitterionic transition structures. 

In support of the above mechanism, spiro[cyclopropane-l,2 -(6 -methyienebicycIo[3.1.0]hexane)] (10) is indeed isolated from thermolysis of the sodium salt of 7-oxospiro[bicyclo[3.2.0]hept-3-ene-2,1 -cyclopropane] tosylhydrazone (9), presumably due to the fact that the corresponding homofulvene would be too strained to form.8 Additional support of the proposed mechanism is also provided by the pyrolysis of the sodium salt of [7,7-2H2]bicyclo[3.2.1]hept-2-en-6-one tosylhydrazone (11), which gives [7,7-2H2]-4-methylenebicyclo[3.1.0]hex-2-ene (12).8... 

A series of metalated alkoxymethyl vinyl ethers has been prepared by the thermolysis of substituted bicyclo[2.2.1]hept-5-enes, one example of which is shown in equation (19). ... 

The addition of diazomethane to cylohexene is so slow and low yielding that such additions only provide a practicable entry to the bicyclo[4.1. OJheptane series if the double bond is activated in some way for example, by conjugation. Hence diazomethane readily underwent addition to cyclohexa-1,3-diene to give 7,8-diazabicyclo[4.3.0]nona-4,7-diene (18 h, 73%), which on thermolysis (110-180 C), photolysis, or sensitized photolysis gave an essentially quantitative yield of bicyclo[4.1.0]hept-2-ene. Cyclohexenes in which the double bond is activated by one ° or exocyclic ester groups or by a carbonyl group in the ring (cyclohexen-... 

Interest in the cyclopentane 1,3-biradical stems not only from its ease of formation from bicyclo[2.1.0]pentane, but also its formation from 2,3-diazabicyclo[2.2.1]hept-2-ene by either thermolysis or photolysis. Remarkably, the gas phase thermolysis of xo-deuterated material gave mostly inverted bicyclo[2.1.0]pentane (Scheme 6.24). ... 

Q 20. Thermolysis of bicyclo[3.2.0]hept-6-ene (I) provided bicyclic lactone (II) with the cis,cis-diene geometry that formally represents a thermally forbidden process. However, thermolysis of bicyclo[6.2.0]dec-9-ene (III) provided bicyclic lactone (IV) with the expected cis,trans-diene geometry. How do you explain this observation ... 

Thermolysis of tricyclo[4,1,0,0 ]hept-3-ene (144) gave a mixture of bicyclo[3,2,0]-hepta-2,6-diene and cycloheptatriene cis,trans,cis- and trans,cis,cis-cyclohepta-triene may be intermediates in these rearrangements. ... 

The generation of carbenes by the thermolysis of lithium or sodium salts of tosyl-hydrazones continues to provide interesting chemistry. The selectivity exhibited by 7-bicyclo[2,2,l]hept-2-enylidene (generated from the corresponding tosylhydrazone) is quite the opposite to that expected from theoretical predictions and earlier studies. Addition to 3,3-dimethylbut-l-ene affords the syn-isomer (118) as the major adduct and consequently any carbene-7i interaction resulting in bridge bending cannot of itself dominate the stereoselectivity of addition. Furthermore, the intramolecular insertion products of 2-methylbicyclo[2,2,l]hept-2-en-7-ylidene have been characterized and, from the product ratios, the species behaves as a true carbene. A 3-furyl-... 

Flash thermolysis of a series of methylated bicyclo[3,2,0]hept-2-ene-7-ones gave dihydrotolualdehydes and tolualdehydes as the major products. The suggested reaction path involved recyclization of a heptatrienal formed from the p,y-unsaturated bicyclic ketones by sequential [2 + 2]cycloreversion to the acyclic ketene and 1,5-hydride shift. 

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