Ring opening/elimination

On reacting nitromethane and acrylonitrile in the presence of TCS 14/triethylamine in benzene (cf. also Scheme 7.42) the oxazolidine 1076, which is obtained in 85% yield, eliminates trimethylsilanol 4 in the presence of TsOH to give 40% d -oxazoline 1077 [104]. Heating of 1076, however, or treatment of 1076 with solid KF leads, via ring opening, elimination of HCN, and rearrangement to d-iso-oxazolidine 1078 in 82% yield this is converted by TsOH, with elimination of 4, into 83% isooxazole 1079 [104]. In contrast with 1076 the isooxazolidine 1080 de-... 

An interesting ring-opening elimination reaction of bicyclic derivative 277 to monocyclic 4//-pyran 278 takes place on thermolysis.140... 

Boron trifluoride-triethylamine effects a ring-opening elimination of 4,4-difluoro-3-trifluoromethyl-l,2-oxathietane 2,2-dioxide to give fluorosulfonyl-trifluoromethylketene. Eliminations occur from intermediate 3-sultones, obtained by addition of sulfur trioxide to alkenes, to give alkenesulfonic acids. ... 

Treatment of diethyl 2,3-epoxypropylphosphonate with a catalytic amount of MeONa in MeOH at 0°C, followed by stirring with Dowex SOW produces irani-3-hydroxy-l-propenylphosphonate in excellent yields (95-100%) by a ring-opening-elimination sequence (Scheme 4.45). 113.132,152,283... 

One model reaction that has proved a popular and appropriate probe for general base catalysis by potential binders of hydrophobic substrates is the Kemp elimination, the simple, single transition state ring-opening elimination of benzisoxazoles 4.19 (Scheme 2.39). 

The radical ring-opening elimination polymerization of 4-methylene-l,3-dioxolane stimulated us to construct a novel template polymerization (3). The concept is that polymers bear polymers. Polymer-supported monomer, which had a structure of 2,2-dipheny 1-4-methylene-1,3-dioxolane, reacted with radical species to afford polyketone and copolymer of styrene with vinylbenzophenone as newborn polymer and template, respectively (Figure 12). These polymers were easily separated by fractional precipitation without any particular chemical treatment after polymerization. On the other hand, common template polymerization requires annoying procedures for the separation of obtained polymers form template. On this point, our novel template polymerization system differs from conventional template polymerization. 

Ring opening in a rather different manner results from exposure of the heterocycle to lithium dimethylamide, followed by trapping with iodomethane, producing an enamine which must result from initial addition at C-2, perhaps by a minor pathway, but one which then leads to ring-opening elimination. ... 

Preliminary evaluations of the SOCM polymers have shown that the mixed radical-cationic polymerizations gave significantly less shrinkage than free radical alone. The polymers obtained from cationic initiation alone exhibited only a small amount of shrinkage which can probably be attributed to the contribution of the single ring-opening/elimination pathway. 

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