Oxiranes 1,3-dioxolane synthesis

In recent years there has been a growing interest in the use of carbonyl ylides as 1,3-dipoles for total synthesis.127-130 Their dipolar cycloaddition to alkenic, alkynic and hetero multiple bonded dipolaro-philes has been well documented.6 Methods for the generation of carbonyl ylides include the thermal and photochemical opening of oxiranes,131 the thermal fragmentation of certain heterocyclic structures such as A3-l,3,4-oxadiazolines (141) or l,3-dioxolan-4-ones132-134 (142) and the reaction of carbenes or car-benoids with carbonyl derivatives.133-138 Formation of a carbonyl ylide by attack of a rhodium carbenoid... 

Nevertheless, a more efficient approach is to attach an electron-accepting atom or radical directly to the chiral carbon atom. Chiral acids and alcohols containing chlorine at the chiral carbon atom can easily be produced from natural amino acids via the Sandmeyer reaction they are widely used in the synthesis of FLCPs [25,26,49,52-54]. A cyano group [55,56] or a perfluorinated alkyl chain [21,57] can also be attached to the chiral center. Lactic acid is a natural chiral product as well, and its derivatives are widely used as chiral terminal groups of FLCPs [27,58-61]. The search for new chiral structures with high transverse dipole moments for FLCPs has resulted in the successful application of heterocycles such as 1,3-dioxolanes [39,62] and oxiranes [63,64]. 

Monofunctionalized PTHF is thus obtained by end capping living polymers with monofunctional initiators. Bifunctional initiators must be used to synthesize bifunctional telechelics. Yamashita has described the synthesis of bis(dioxolan-2-ylium) cations (60) and their use as initiators for the polymerization of THF. Bi- and tri-functional initiators (61)-(63) were synthesized by Penczek and co-workers. Chains reportedly grow independently at all sites, and copolymers can be formed if 10-20% of THF is replaced by methyl oxirane. ... 

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