Skeletal Rearrangements of a Diterpene

Reaction of methyl pimarate 1 with bromine in THF/H2O in the presence of NaHC03 for 10 minutes at 0°C gave a mixture of the products 2 (41%), 3 (18%), 4 (5%) and 5 (11%). The 6-6-7 system in 2-5 is the skeleton of the strobane diterpenes, and the 1 — 2-5 process has been claimed to provide a biomimetic access to strobane derivatives . 

Studies of the reactions of quinoxaline N-oxides under Reissert reaction conditions have led to some very interesting and unusual results. Thus, treatment of quinoxaline IV-oxide with PhCOCl/KCN in methanol or water under standard Reissert conditions gave 6-chloroquinoxaline as the major product (ca. 45%), and only small amounts of the desired 2-cyanoquinoxaline. Use of 3 equivalents of TMSCN in place of KCN and dichloromethane as solvent, however, gave 2-cyanoquinoxaline in 72% yield. When 2,3-diphenylquinoxaline iV-oxide was treated with 1 equivalent of PhCOCl in the presence of 3 equivalents of either KCN or TMSCN a mixture of products was always obtained irrespective of the solvent used. The most interesting of these products was the ring cleaved compound 1. 

Elucidate these various transformations and suggest a mechanism for the formation of 1. 

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