Octavalene

Intramolecular cyclopropanation of [(7 H-benzocycloheptene-7-yl)diazomethyl]-diphenylphosphinoxide 172 represents the first synthesis of a benzo-annulated octavalene (173)180). Not unexpectedly, carbenic rearrangement products 174 and 175 are also formed. 

Christl and Lang (390) noticed an upheld signal shift of about 10 ppm when they compared the methine carbon atoms in bicyclo[1.1.0]butane (287) (391) and octavalene (288). On the other hand, in benzvalene (289), the corresponding shielding is +48.3 (203), because in this molecule back-donation from the Walsh orbitals to the ir -orbital of the olefinic group (290) is conceivable. Such an interaction is not possible in 288, because the ir -orbital of the diene chromophore is of different symmetry (390). 

It is not unreasonable to expect preparatively useful photoreactions of appropriately functionalized dihalocyclopropanes also. Although the present trend in gew-dihalocyclopropane chemistry clearly favors the use of more highly functionalized substrates, the traditional role — mentioned in the introduction — of employing these strained molecules in hydrocarbon synthesis, is by no means an approach of the past. This point is stressed by the recent synthesis of octavalene... 

The butadiene bridge of octavalene (59) widens the angle at the central carbon the rather high field central carbon shows Jc(1)h == 207 Hz and the much lower field allylic carbon C(2) has a normal value Jq2)h = 1 2 Hz. From a comparison of the values of Jqh octavalene and 96 it appears that any correlation between the magnitude of Jqh and the probable angle between the three-membered rings is not securely established. 

Octavalene (tricyclo[5.1.0,0 ]octadiene, O) gives COT in boiling benzene (Scheme 9.18). ... 

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