Oxonium ylides cyclic

Besides [2,3]-sigmatropic rearrangement and [l,2]-shift reactions, the oxonium ylide may undergo other reactions. The oxonium ylide intermediate can be trapped by a protic nucleophile. Oku and co-workers have developed a method for ring expansion of cyclic ethers through oxonium ylide formation. Bicyclic oxonium ylide... 

Cyclic mixed acetals with pendant diazo ketone side-chains undergo rearrangement to ether-bridged cycloheptane ring systems on treatment with Cu(hfacac)2.118 A Stevens [1,2]-shift of an oxonium ylide gives the major product (62), in some cases accompanied by minor amounts of a product (63) resulting from a [l,2]-shift of a sulfonium ylide. 

The rhodium acetate-catalyzed decomposition of l-diazo-4-(benzyloxy)butan-2-one and related compounds offers a way to substituted tetrahydrofuranones a Stevens [ 1,2]-shift of a cyclic oxonium ylide is involved in this reaction (Equation (89)) <92J0C3479>. 

Scheme 16.4 Cyclic ether scaffolds within complex targets via oxonium ylides.

The combination of reactions of rhodium carbenoids with polyether-macrocycle synthesis offered interesting procednres for the synthesis of this important class of compounds. One elegant example is the Rh-catalyzed four-component reaction of two a-diazo- 3-keto esters and two cyclic ethers, such as tetrahydrofuran or 1,4-dioxane, to yield functionalized 16- to 18-membered macrocycles 65 (Scheme 5.44) [42]. The process involves the generation of electrophilic rhodium carbenoid A, the addition of cyclic ether to this intermediate, as well as the formation and dimerization of the oxonium ylide intermediate B. Another example is the Rh-catalyzed macrocyclization of oxetanes with a-diazocarbonyls (Scheme 5.45) [43]. In this case, three oxetanes and one rhodium carbenoid intermediate condense in a one-step process. It is noteworthy that these macrocyclizations could proceed under high-concentration conditions (1M). 

Cyclic oxonium ylides building blocks for iterative synthesis of polycyclic ethers. Marmsater, F.P., Vanecko, J.A., West, F.G. (2002), Tetrahedron, 58, 2027-2040. The art and science of total synthesis at the dawn of the twenty-first century. Nicolaou, K.C., Vourloxunis, D., Winssinger, N., Baran, P.S. (2000), Angew. Chem. Int. Ed., 39, 44-122. 

Ammonium ylides undergo [l,2]-shift in a manner similar to oxonium and sulfonium ylides. A preferentially migrating group is usually a benzyl group. A sequence of intramolecular formation of ammonium ylide and subsequent rearrangement was extensively explored by West and co-workers in the synthesis of cyclic amines. ... 

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