Enol ether structures

No systematic IR spectroscopic studies have been reported. The value for the C-C double-bond stretching frequency of the enol ether structure in 2,7-dimethyloxepin is 1660cm-1.12... 

In general, BF3 -catalyzed Mukaiyama reactions lack a cyclic organization because of the maximum coordination of four for boron. In these circumstances, the reactions show a preference for the Felkin type of approach and exhibit a preference for syn stereoselectivity that is independent of silyl enol ether structure.119... 

The isolation of pyruvaldehyde enol ethers rather than glyceraldehyde structures during mild acidic hydrolysis may indicate that the latter structures are not stable in their free form but tend to lose water to produce pyruvaldehyde enol ether structures. Such structures may therefore be formed in lignin during technical processes carried out under mild acidic conditions such as the production of TMP. Pyruvaldehyde enol ether structures absorb UV-light above 300 nm and may thus contribute to the photo-yellowing process. Under conditions simulating the production of CTMP, on the other hand, it was previously shown that these types of structures are rapidly and completely eliminated presumably by sulfonation reactions (75). 

Gellerstedt G, Lindfors EL (1987) On the formation of enol ether structures in lignin during kraft cooking Nord Pulp Pap Res J 2 71-75... 

By using the p-methoxy-substituted enamide (192), Ninomiya et al. (54) succeeded in a simple synthesis of alloyohimbone (196) via the unconjugated lactam 194, which has an enol ether structure. Lithium aluminum hydride reduction of the lactam 194, followed by hydrolysis with hydrochloric acid and subsequent catalytic hydrogenation over platinum dioxide, yielded alloyohimbone (196) stereoselectively in an overall yield of 59% from harmalane (54) this was the most convenient synthesis of alloyohimbone (196) so far reported (Scheme 75). 

Particular attention has been devoted to the fate of Cf,C2 enol ether structures present in kraft or soda lignins (Gellerstedt et al. 1984). It has been shown that such structures are essentially converted to a C(,C2 product with two thioethyl groups at C. This dithioacetal compound is formed only in small amounts on thioacidolysis of QC3 y -aryl ether structures. Therefore, when present in significant amounts in the thioacidolyzate of a sample, the dithioacetal compound is indicative of 02 enol ether structures preexisting in the sample. 

Fischer, P, Enol ethers — structure, synthesis and reactions, Chem Ethers, Crown Ethers, Hydroxyl Groups Sulphur Analogues, 2, 761-820, 1980. 

G Gellerstedt, EL Lindfors. On the Formation of Enol Ether Structures in Lignin during Kraft Cooking. Nordic Pulp Pap Res J 2 71-75, 1987. 

A range of acylic silyl diketonates and cyclic acetylacetonates have been reported, which possess enol ether structures with acyl cis or irons to the silyl group. The ratio of cis to irons in both series appears to depend on the incipient... 

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