Hepta-1,2,6-trienes rearrangement

The two-step process, depicted by path b, involves initial addition of the carbene carbon to an adjacent it bond to form bicyclo[4.1,0]hepta-2,4,6-triene (2a). This process has precedent in the analogous rearrangement of vinylcar-bene to cyclopropene (Scheme 6),lc18 and is supported by Gaspar s work on 1-cyclohexenylcarbene.17 In the second step of the mechanism in Scheme 5, subsequent six-electron electrocyclic ring opening of 2a yields the cyclic allene 3a. 

Scheme 6.114, a carbene-carbene rearrangement transforms diphenylcarbene to o-phenylphenylcarbene, which is the progenitor of 565. Two phenylbicydo[4.1.0]-hepta-2,4,6-trienes and l-phenyl-l,2,4,6-cycloheptatetraene (562) have to be assumed as further intermediates. The participation of 562 is supported by the structure of the products 563 and 564, which should result from the addition of 562 to diphenylcarbene and the dimerization of 562, respectively. By thermolysis of the sodium salt of 2-phenyltropone tosylhydrazone, 562 was generated directly. At 100 °C in diglyme as solvent, 564 was identified as the only product and at 340°C/4Torr in the gas... 

The cyclic diradical, 2-methylene-1,4-cyclohexadiyl (18), can be formed from the hepta-1,2,6-triene 1722,23. Thermolysis of 17 gives 3-methylene-l,5-hexadiene 19 as a Cope rearrangement product, while the same treatment (155 °C, benzene) in the presence of SO2 leads to sulfones 20 and 21 instead of 19 (equation 6). It was shown that sulfone 20 is obtained by reaction of SO2 with the rearrangement product 19, while sulfone 21 originates directly from the diradical 18. 

Another paper64, which also contains a literature survey about the problem discussed, describes the rearrangements of C7H6 systems which can be generated by thermolysis of phenyldiazomethane. By using spectral methods and chemical reactions, the formation of bicyclo[4.1.0]hepta-2,4,6-triene (139), cycloheptatrienylidene (137a) and bicyclo[3.2.0] hepta-l,3,6-triene (135) was excluded, and evidence for the formation of intermediate cycloheptatetraene (137b) (see equation 45) was furnished. 

The prototype of this reaction is the Myers-Saito reaction, the rearrangement of eneyneallene (Z)-hepta-l,2,4-triene-6-yne (70) to a,3-didehydrotoluene (71). This C2—C7 cyclization yields a benzylic 7i-conjugated a,7t-biradical and is therefore... 

Unlike phenyldiazomethane which is converted on irradiation into cyclohepta-1,2,4,6-tetraene, the carbenes (52) generated by photodecomposition of the naphthyldiazomethanes (53) undergo rearrangement to the benzobicyclo[4,1.0]hepta-2,4,6-trienes (54). Hydrogen abstraction by triplet diphenylcarbene is observed on photodecomposition of diphenyldiazomethane in cyclohexane, whereas singlet-derived solvent insertion reactions compete with hydrogen... 

The inner phase photolysis studies of 4094 uncovered a novel photochemical reaction of 95. Under the photolysis conditions, 95 underwent efficient photochemical electro-cyclization to the anfi-Bredt imine 100, which at -5°C thermally rearranged via a 1,5-shift to the slightly more stable l-azaspiro[2.4]hepta-l,4,6-triene 101. 

The gas phase rearrangements of phenyl carbene, particularly the conversion to cycloheptatrienylidene, which is actually 1,2,4,6-cycloheptatetraene, and probably involving bicyclo[4.1.0]hepta-2,4-6(7)-triene, are particularly fascinating (Scheme 8.6). ... 

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. ... 

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