Allyl substituted-5 -oxazolones

Very recently, Shi and co-workers [134] demonstrated that the chiral thiourea-phosphine was an efficient catalyst in the enantioselective allylic substitution of BH carbonates using oxazolones as nucleophiles. The reaction catalyzed by 75 afforded the corresponding products in good to excellent yields and enantioselectivities as well as moderate to good diastereoselectivities (Scheme 9.37). 

The UV irradiation of the 2-allyloxy-4,5-diphenyloxazole 41 results in the predominant formation of 5-substituted-2(5/T)-oxazolones 44, in contrast to the thermal aza-Claisen rearrangement which readily affords the 2(3/T)-oxazolones 42. The photolysis proceeds via allyl-O bond scission with the generation of a radical pair that subsequently recombines to produce 5-substituted-2(5/T)-oxazolones. Similar results were obtained with 2-(benzyloxy)-4,5-diphenyloxazole (Fig. 5.75). °... 

Allyloxy-substituted 4,5-diphenyloxazoles undergo [3,3]-sigmatropic aza-Claisen rearrangements to 3-allyl-2(3//)oxazolones <84JOC399>. The 2-propynyloxy-oxazole (61) affords an allene... 

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