Orthoester spiro

Details are given of the successful construction of a novel reversible system of network polymers between bifunctional monomers by utilising the equilibrium polymerisation system of a spiro orthoester. Molecular structures were determined by NMR and IR spectroscopy. 9 refs. 

Descotes et al. developed a stereoselective photocyclisation procedure of hydrox-alkyl glycosides to give spiro orthoesters [135]. By oxymercuration of the glycal 154... 

This reaction is thermodynamically controlled, because the polymer containing 1,3-dioxolane rings converts itself to a polyether when allowed to stand at room temperature for several days or heated at 80 °C for a few hours in the presence of an acid catalyst. Similar double ring-opening polymerizations were observed for 2,6,7-trioxabicyclo[2.2.2]octane and its derivatives [86, 87] and for spiro orthoesters and spiro orthocarbonates as well (see Sects. 6 and 7). 

Spiro orthoesters (92, R = Me, Ph, and H) show typical equilibrium polymerization behavior at or below ambient temperature. [92] The poly(cyclic orthoester)s derived from 92 depolymerize to the monomers, although they have sufficient strains to be able to undergo ring-opening polymerization. The polymerization enthalpies and entropies for these three monomers were evaluated from the temperature dependence of equilibrium monomer concentrations (Table 5). The enthalpy became less negative as the size of the substituent at the 2-position in 92 was increased H < Me < Ph. This behavior can be explained in terms of the polymer state being made less stable by steric repulsion between the bulky substituents and/or between the substituent and the polymer main chain. The entropy also changed in a similar manner with the size of the substituents. 

Table 5. Thermodynamic parameters AH° and AS° for polymerization of spiro orthoester 92 [92]...

Polymerization of spiro orthoester 96 accompanied a 2.7% volume expansion. This behavior is similar to that observed in the polymerization of nonfluorinated spiro orthoester 99 (0.9% expansion). Thus, it appears that the perfluoroalkyl group does not significantly affect the feature of zero shrinkage during the polymerization of sipro orthoesters. 

Endo, Suzuki, Sanda, and Takata [57] showed (Fig. 14b) that dithiol-linked bifunctional spiro orthoesters 48 can generate cross-linked polymers 49 in the bulk under acidic conditions (2 mol% CF3COOH). The increase of the temperature shifts the equilibrium in favor of the monomer. Conversely, the cross-linked polymers can be depolymerized from CH2C12 suspensions to form the initial monomers, also under acidic conditions (5 mol% CF3COOH). The yield of these processes is not quantitative. 

Patent Synthesis of Spiro Orthoesters, Spiro Orthocarbonates, and... 

Formation of spiro orthoesters such as 4 is achieved in high yield by reaction of cyclic ketene monothioacetals such as 3 with ethanediol and camphorsulfonic acid <04SL2013>. A variety of substituted epoxy ketones 5 rearrange to the benzodioxoles 6 upon treatment with Bu.,N CN in CHjClj or K1 in acetone <04T3825>. Condensation of phenacyl carbonates 7 with aromatic aldehydes in the presence of MgCClO ), 2,2 -bipyridyl, A-methylmorpholine and molecular sieves gives the trans dioxolanones 8 <04SL1195>. 

Spiroketals have been obtained by RCM of cyclic ketals 18 without loss of stereochemical integrity at the spiro linkage <04TL5505> and a stereoselective solid-phase synthesis of 6,6-spiroketals has been reported in which aldol reactions of boron enolates are the key feature <04AG(E)3195>. Spiro orthoesters are accessible from thiophenyl ketene acetals and diols (Scheme 5) <04SL2013>. 

A number of spiro orthoesters have been synthetized and the volume changes during the cationic ring-opening polymerization have been studied46. ... 

Figure 16. Radical ring-opening polymerization of spiro orthoester derivatives with exo-methylene group.

Figure 1. Polymerization of a methacrylate-substituted spiro orthoester (1) by free radical addition to the methacrylate group followed by cationic ring opening.

Figure 2. Structures of an alternate spiro orthoester methacrylate (2) and the Spiro orthocarbonate methacrylate (SOCM, 3) monomer.

IR frequencies of functional groups, 206 polymer characterization procedure, 205 polymer synthetic procedure, 204 postpolymerization schedules, 204,205t properties, 206,207t study procedure, 205-206 Acrylate-containing spiro orthoesters, structures, 172,173/... 

Interesting syntheses have been reported of Escherichia coli lipid A (218), of the pseudo-trisaccharide destomycin C (219), which as well as a cyclitol fragment contains an unusual spiro-orthoester interglycosidic linkage, and of the anthracyclinone sugars daunosamine (220) and acosamine (221). ... 

Crivello and Lam have demonstrated the use of diaryliodonium salts as photoinitiators for polymerization of electron-rich olefins, cyclic ethers, cyclic sulfides, lactones and spiro orthoesters, but a vast majority of their published work concerns polymerization of substituted oxiranes, illustrating the potential of such systems in photocuring of epoxy resins. Such polymerizations can be quite fast in the most favorable example, a 93% yield of polymer of Mn 10,700 was obtained from 3-vinylcyclohexene oxide after only 90 seconds of irradiation at room temperature with 4,4 -di-tert-butyldiphenyliodonium hexafluoroantimonate as initiator (3). The substituted salts are often preferred to the simple unsubstituted diphenyliodonium compounds for reasons of solubility (2). The use of diaryliodonium salts in combination with various dyes allows one to initiate cationic polymerization with visible light (5). 

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