Synthesis of 1-Cyclohept-1,2-dien-1-yl benzene from 1-(2-iodo-, chlorocyclohept-1-en-1yl) benzene and 1-(2-iodo-, chlorocyclohept-2-en-1yl) benzene: Its trapping with diphenylisobenzofuran

The key compounds vinyl iodides 12a and 13a, for the generation of 1-cyclohept-1,2-dien-1-ylbezene (1), were synthesizedf rom cycloheptanone (5). Bromobenzene was convertedt o the Grignardreagen t, which was condensed with 5. Dehydration of alcohol 6 gave alkene 7. Hydroboration of 7 followedb y oxidation with PCC afforded ketone 9, which was convertedt o hydrazone 10. Treatment of 10 with iodine resulted in the formation of 12a and 13a. The other precursors, 12b and 13b, were synthesized from the reaction of 9 with $PCl_5$. Reactions of 12a, b and 13a, b with KOtBu in a sealedt ube at 185 ◦C gave the [2+4] and [2+2] dimer products 20 and 21, respectively. In addition, reactions of 12a, b and 13a, b with KOtBu under the same conditions in the presence of diphenylbenzoisofuran (DBI) as a trapping reagent afforded the [2+4] cycloadducts 24 and 25 in goody ields.

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