2,3-epoxy alcohols 3,2-shift

In the reaction of the conformationally restricted epoxy alcohol 84 and methyl or benzyl isocyanate, the epoxy carbamate 85 was formed. Cycliza-tion of 85 in tetrahydrofuran in the presence of sodium hydride gave the oxazinone 86 in approximately 20% yield, and the oxazolidinone 87 (R = Me, CH2Ph) in 40-60% yield. The formation of the two products can be rationalized by different nucleophilic attacks on the urethane nitrogen. With increasing nucleophilicity of the nitrogen, the regioselectivity of the reaction is shifted toward the formation of 87 (92TL3009). 

Epoxy-3-alcohols can be derived from 2,3-epoxy-1-alcohols by the base-catalyzed Payne rearrangement as illustrated in step d of Figure 6A.4 [59,64], The rearrangement is completely stereospecific but, because it is reversible, it usually results in an equilibrium mixture of the two epoxy alcohols for which the relative proportions are structure-dependent. Practical synthetic applications of this rearrangement therefore depend on methods that will shift the equilibrium completely in the direction desired. Nucleophiles such as thiolates and amines are... 

Eliminations of (3,4-epoxybutyl)stannanes under the action of EtAlCl2 give rise to cyclo-propylmethyl alcohols <87SC78l, 91JOC2066,91JOC2076). This method can be used reliably to prepare bicyclo[3.1.0]hexanes from the corresponding spirocyclic epoxy stannanes (Equation (9)). These eliminations appear to be concerted when inversion can take place at both centers. In other cases, the 1,3-eliminations are stepwise and must compete with 1,2-hydride shifts. 

A relation was developed in Figure 19 for effect of the hydroxyl to epoxy ratio on the initial rate of reaction. As the hydroxyl concentration rises, the initial rate of reaction increases this would probably hold true until dilution effects dominate. Similar relations have been developed by Bowen and Whiteside (29). It should be further noted that this curve represents isopropyl alcohol as the hydroxyl source. The slope would shift for other alcohols depending on their reactivity. 

Thermal Stability and Conductivity. Thermal degradation temperature of PMMA, PS, and PVA (poly(vinyl alcohol)) nanocomposites shifts up by 10-100°C. During combustion [179], nanoparticles form a network of char layers that retards the transport of decomposition products. The thermal conductivity of epoxy composites is four times higher than that of the neat epoxy resin with 5 wt% loads. 

The first step in the mechanism is the reaction of DICY with epoxy to form the alkylated DICY. This was confirmed by the imide IR peak at 1570 cm The second step involves further alkylation of the nitrogen that reacted in step 1, to form the AA(-dialkyldicyandiamide. No alkylation of the other amino group was suggested. The third step is the intramolecular cyclization step to form a zwitteri-onic five-membered intermediate. This involves the intramolecular reaction of the secondary alcohol formed in step 2 with the imide functionality (—C=N—). This is in contrast with the Zahir mechanism (112) where the intramolecular cyclization involves the hydroxy and the nitrile groups. The fourth step involves the elimination of ammonia and the formation of 2-cyanimidooxazolidine. The formation of this heterocycle is consistent with the observed bathocromic IR shift from 1570 cm to 1650 cm The ammonia that is eliminated can then react with epoxy to form a trifimctional cross-hnk. The last step involves the hydrolysis of the oxa-zolidine to form the oxazoUdone and cyanamide. The hydrolysis step accounts for the formation of the carbonyl group. 

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