Oxirane, and its derivatives

Most polymerizations of cyclic monomers are ionic processes. Coordination catalysts are effective only for some heterocycles (oxirane and its derivatives, lactones). Ziegler-Natta catalysts can only be used for cycloalkene polymerization by metathesis heterocycles act as a catalytic poison. Smooth radical polymerization of hydrocarbon monomers with ring strain is unsuccessful [304], The deep-rooted faith that ring strain represents a major contribution to the driving force in ring opening (polymerization) has to be revised [305, 306]. 

Frankvoort (1977) presented another type of adiabatic reaction calorimeter for liquids. He established the adiabatic condition by running the same reaction at identical conditions (concentration, temperature) in the container surrounding the calorimeter vessel. He and his coworkers determined the kinetic constants of the acid hydrolysis of oxirane and its derivatives. This technique is, however, only of historical interest nowadays. 

Oxirane and its simple alkyl derivatives do not absorb in the region of the UV spectrum routinely used for structure determination (above 200 nm). Oxirane itself shows at... 

Spectra and Theoretical Chemistry of Oxirans. - The use of conformational analysis, with the aid of torsion-angle notation, permits the interpretation and prediction of regioselective opening of epoxides/ Values for the molar refraction, electron polarization, and permanent electron dipole moments for oxiran and its simple derivatives have been calculated from literature data/ The molar Kerr constants for oxiran and its methyl derivatives in CCI4 were also calculated. The pericyclic reactivities of three-membered heterocycles have been rationalized, using the relaxation method. ... 

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]. 

For the oxirane and thiirane derivatives, different types of disconnections are preferred (Scheme 5.26). The epoxide in TM 5.10 can be disconnected to alkene and a source of oxygen. In the synthetic direction, convenient epoxidation agents are peracids, in particular meta-chloroperbenzoic acid (MCPBA). This reagent is produced on the industrial scale by chlorination and then oxidation of benzoic acid and, due to its selectivity and solubility in most organic solvents, is used for epoxidation of complex molecules even on the large scale [6]. 

Table lll-E-22. Rate coefficients (k, cm molecule oxirane and its methyl-substituted derivatives... 

Among the monomers given in Scheme 1, several possess sufficient nucleophilicity to undergo cationic polymerization (7,8), namely 2-vinyltetrahydrofiiran 1, the alkenylfiirans 2, the furfurylidene ketones 3, 2-furyl oxiranes 4 and the furfuryl vinyl ethers 6, Moreover, furfural and its 5-methyl derivative can act as comonomers in certain cationic copolymerizations. 

By contrast, lithium enolates derived from tertiary amides do react with oxiranes The diastereoselectivity in the reaction of simple amide enolates with terminal oxiranes has been addressed and found to be low (Scheme 45). The chiral bicyclic amide enolate 99 reacts with a good diastereoselectivity with ethylene oxide . The reaction of the chiral amide enolate 100 with the chiral oxiranes 101 and 102 occurs with a good diastereoselectivity (in the matched case ) interestingly, the stereochemical course is opposite to the one observed with alkyl iodides. The same reversal is found in the reaction of the amide enolate 103. By contrast, this reversal in diastereoselectivity compared to alkyl iodides was not found in the reaction of the hthium enolate 104 with the chiral oxiranes 105 and 106 °. It should be noted that a strong matched/mismatched effect occurs for enolates 100 and 103 with chiral oxiranes, and excellent diastereoselec-tivities can be achieved. 

Polymerization of oxirane (and of its derivatives) by the mechanism of activated monomer is so far exclusively cationic and can be represented by schemes (27) and (28) of Chap. 4. In contrast to the ring-opening polymerization of lactams, both the classical and the activated monomer mechanisms are operating in this case. Conditions can be found where one or the other mechanism predominates [339]. 

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