Cycloheptene. reaction + carbenes

The results of the reactions involving these carbenes are compiled in Table 14. Irradiation of 5-diazo-10,l l-dihydrodibenzo[a,c/]cycloheptene with a high-pressure mercury lamp gives 10,11-dihydrodibenzo[a,rf]cyclohepten-5-ylidene, which can be trapped under the right conditions. When the photolysis was carried out in the presence of ( )-l-phenylprop-l-ene, stereospecific cycloaddition took place to give rra i-3-methyl-l-phenylspiro[cyclopropane-2,5 -10, lT-dihydro-5 //-dibenzo[a,cf]cycloheptene in 19% yield.Efficient trapping even on a synthetic scale is experienced when the diazo compound is irradiated in various styrenes. Thus, when 4-methoxystyrene was used as solvent l-(4-methoxyphenyl)spiro[cyclopropane-2,5 -10, lT-dihydro-5 7/-dibenzo[a,ii]cycloheptene (1) was isolated in 81% yield in addition 5,5 -bi(10,ll-dihydro-5//-dibenzo[u, f]cycloheptyl) (2) was obtained in 11% yield. 

Thus photolysis of the tosylhydrazone sodium salt of 5//-dibenzo[a,c]cyclohepten-5-one (14) at — 60 °C in the presence of cyclopentadiene or furan with tetrahydrofuran as cosolvent gave the cyclopropene Diels-Alder adducts 17 and 18 in 73 and 47% yields, respectively. If the photolysis was stopped shortly after all the tosylhydrazone salt had decomposed, adduct 17 was the only isomer found in the cyclopentadiene reaction. In the formation of the furan adduct 18, the reaction was not so clean and a number of unidentified products were also formed. Unfortunately, adduct 18 is thermally unstable at the temperature necessary for thermal formation of carbene 15. No trace of adduct 18 was detected when the arylcarbene 19 was generated directly from its tosylhydrazone salt in the presence of furan. ... 

Systems 4 and 5 provide an interesting contrast. The thermodynamic stability of the cyclohepten-5-one derivative produced in system 4 effectively prevents any units of M2 from being incorporated in the polymer of Mi. The carbonyl group is evidently sufficiently protected to prevent it from undergoing a Wittig-like reaction with the metal carbene complex. 

Cycloheptenes and cyclooctenes on irradiation, in addition to cis-trans-iso-merization, undergo ring contraction and carbene insertion reactions [6, 7]. 

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