Triene complexes alkene termination

Transformations shown in Schemes 12-14 constitute the first examples of catalytic AROM reactions ever reported. Meso-triene 50 is converted to chiral heterocyclic triene 51 in 92% ee and 68% yield with 5 mol% 4a (Scheme 12) [21]. Presumably, stereoselective approach of the more reactive cydobutenyl alkene in the manner shown in Scheme 12 (II) leads to the enantioselective formation of Mo-alkylidene III, which in turn reacts with an adjacent terminal olefin to deliver 51. Another example in Scheme 12 involves the net rearrangement of meso-bicycle 52 to bicyclic structure 54 in 92% ee and 54% yield. The reaction is promoted by 5 mol% 4a and requires the presence of diallyl ether 53 [22], Mechanistic studies suggest that initial reaction of 53 with 4a leads to the formation of the substantially more reactive chiral Mo=CH2 complex (vs neophylidene 4a) which can react with the sterically hindered norbornyl alkene to initiate the catalytic cycle. 

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