Oxetanes, from epoxides

Abstract This chapter focuses on well-defined metal complexes that serve as homogeneous catalysts for the production of polycarbonates from epoxides or oxetanes and carbon dioxide. Emphasis is placed on the use of salen metal complexes, mainly derived from the transition metals chromium and cobalt, in the presence of onium salts as catalysts for the coupling of carbon dioxide with these cyclic ethers. Special considerations are given to the mechanistic pathways involved in these processes for the production of these important polymeric materials. 

R" may be alkyl or aryl. For dialkyl ethers, the reaction does not end as indicated above, since R OH is rapidly converted to R OR by the sulfonic acid (reaction 0-16), which in turn is further cleaved to R 0S02R" so that the product is a mixture of the two sulfonates. For aryl alkyl ethers, cleavage always takes place to give the phenol, which is not converted to the aryl ether under these conditions. Ethers can also be cleaved in a similar manner by mixed anhydrides of sulfonic and carboxylic acids733 (prepared as in 0-33). p-Hydroxy alkyl perchlorates734 and sulfonates can be obtained from epoxides.735 Epoxides and oxetanes give dinitrates when treated with N2Os,736 e.g.,... 

Physical Methods for the Characterization of Copolymers Produced from Epoxides or Oxetane and Carbon Dioxide... 

Therefore, from epoxide 83 (Scheme 5.38), a 1,2-phenyl shift in intermediate MM would provide oxonium derivative NN, which would furnish, after rearrangement of the oxetane intermediate OO, the desired ketone 84. It is interesting to note that on the same substrates cationic gold derivatives (activated with silver salts) did not lead to the same final compounds, showing the unique reactivity of silver salts. 

Oxetans.—Stable oxetens are rare another example (56), this time stabilized by the pstfluoroalkyl effect , has been reported. The Paterno-Buchi reaction cannot be used for the synthesis of 2,2-dialkyl-oxetans from aliphatic ketones. A convenient, one-step conversion of such ketones into oxetans involves use of the sulphoximide (57) and proceeds via ring-expansion of an epoxide intermediate. Unusually high asymmetric induction has been observed in the Paterno-Buchi reaction of (-)-menthyl phenylglyoxylate with tetramethylethylene. The visi-... 

Teipolymers form from epoxides, anhydrides, and tetrahydrofuran or oxetane with a trialkylalu-minum catalyst ... 

Formation of Allyl and Aryl Primary AUyUc and HomoallyUc Alcohols from Vinyl Epoxides and Oxetanes. Vinylic epoxides can be coupled with aryl (eq 30) or vinyl (eq 31) iodides or tri-flates to form allylic alcohols in 40-90% yield. When employing palladium acetate as the catalyst, a reducing agent such as sodium formate is required in addition to the salts normally present under phase transfer conditions. 

The use of oxetanes for the synthesis of polynitrate esters is generally of less value than the use of epoxides, which are readily available from the epoxidation of alkenes. The analogous reaction of azetidines with dinitrogen pentoxide is a route to 1,3-nitramine-nitrates and these reactions are discussed in Section 5.8.2. ... 

Deuterium incorporation from the solvent may occur in the last step and in the equilibrium 111<= 112. The fact that epoxides originating from terminal > C+ olefins show deuterium retention can be reasoned in two ways either the formation of ironoxetanes is disfavored due to steric interactions or the internal base acting on the oxetane cannot operate due to steric constraints and consequently the long chain olefins have to depart from 111 by reductive elimination. 

In this chapter, some of the essential aspects of the synthesis and characterization of copolymers derived from the coupling of C02 with various monomers, namely, epoxides, oxetanes, and aziridines, have been reviewed. In addition, the use of carbon disulfide as a resource for copolymer production was introduced, and the present understanding of the mechanistic aspects of processes involving cyclic ethers and C02 catalyzed by well-defined metal systems has been emphasized. This knowledge has led to the development of catalytic systems capable of controlling not only the product selectivity but also the regio- and stereoregularities of the resultant copolymers. 

To our knowledge, no work dealing with the cationic telomerisation of fluorinated alkenes has been described in the literature in contrast to successful works achieved from fluorinated epoxides [69,70] or oxetanes [71]. 

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