Cycloadditions cycloheptadiene formation

In particular the synthetic approach to dihydrofurans (first equation in Figure 4.23) represents a useful alternative to other syntheses of these valuable intermediates, and has been used for the preparation of substituted pyrroles [1417], aflatoxin derivatives [1418], and other natural products [1419]. The reaction of vinylcarbene complexes with dienes can lead to the formation of cycloheptadienes by a formal [3 + 4] cycloaddition [1367] (Entries 9-12, Table 4.25). High asymmetric induction (up to 98% ee [1420]) can be attained using enantiomerically pure rhodium(II) carboxylates as catalysts. This observation suggests the reaction to proceed via divinylcyclopropanes, which undergo (concerted) Cope rearrangement to yield cycloheptadienes. 

A rare example of formation of cycloheptadiene from 1,3,8-triene was reported by Hiemstra et al. in the enantioselective synthesis of the tetracyclic left-hand substructure 301 of solanoeclepin A (302) (Scheme 1.55) [75]. Starting from compound 303, a [4-1-2]-cycloaddition was used to elaborate the oxabicyclic motif Nolan s catalyst [Ru]-VI (15 mol%) was used to cyclize the 1,3,8-triene 305 to the desired cycloheptadiene 306 in quantitative yield. It is worth mentioning that [Ru]-I was quite inefficient in this case even if a stoichiometric quantity was used. 

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