Hydroxymethyl groups elimination

All of these ehimnddon reacdons contain fi-carbonyl groups in the nltro compounds Of course, masked carbonyl groups are also frequently employed for such fi-elimination of HNO, as shown in Eq 7131, Eq 7 133, and Eq 7 133In these cases, the sulfinylmethyl or hydroxymethyl group is converted into the carbonyl group by the Pummerer rearrangement or by simple oxidation... 

Condensation reactions between two hydroxymethyl substituents eliminate water to form ether linkages (Fig. 7.23a) or eliminate both water and formaldehyde to form methylene linkages (Fig. 7.23b). Ether formation is favored under neutral or acidic conditions and up to 130°C above which formaldehyde departs and methylene linkages are generated. The methylene linkage formation reaction, which eliminates water and fortualdehyde, is more prevalent under basic conditions. Condensation reactions between hydroxymethyl groups and reactive... 

Thermal degradation below 300°C in inert atmospheres produces only small amounts of gaseous products. These are mostly unreacted monomers or water, which are by-products eliminated from condensation reactions between hydroxymethyl groups and reactive ortho or para positions on phenolic rings. A small... 

These pre-condensates are most stable at pH 8-9 they are transformed by further condensation (essentially by elimination of water from hydroxymethyl groups and free NH groups) into poorly soluble and Anally insoluble, crosslinked products. Chemical modification of the soluble pre-condensate, for example, by esterification or ether formation, is again possible. 

The reaction of 3-hydroxymethyIpyridine 1-oxide with methyl fluorosulfonate and potassium cyanide provides a direct method for 2,6-dicyanation (75JOC2092). However, the generality of this method is limited by the need for a 3-substituent that can form an anhydrobase. In this example (Scheme 138) the anhydrobase is formed by methylation of the 3-hydroxymethyl group followed by elimination either during or subsequent to attack by the second mole of cyanide. The use of such a powerful methylating agent overcomes... 

It is noteworthy that structures like such as 71 are generally more favourable to elimination reactions, because of the particularly high acidity of the hydroxylic hydrogen. Indeed, for the mixed salt 72, the hydroxymethyl group is preferentially eliminated692 (reaction 204). 

Free Phenolic Structures Containing /3-Ary I Ether Bonds The first step of the reaction involves the formation of a quinone methide from the phenolate anion by the elimination of a hydroxide, alkoxide, or phenoxide ion from the a-carbon (Fig. 7-25). The subsequent course of reactions depends on whether hydrosulfide ions are present or not. In the latter case (soda pulping), the dominant reaction is the elimination of the hydroxymethyl group from the quinone methide with formation of formaldehyde and a styryl aryl ether structure without cleavage of the /8-ether bond (Fig. 7-26). When hydrosulfide ions are present (strong nucleophiles) they react with the... 

C]Cholesterol was readily converted into 19-nor-sterols by the sponge Axinella polypoides, but very little de novo synthesis of these sterols from [1-14C]acetate occurred.354 Similarly, whilst [4-14C]cholesterol was incorporated into 3/3-hydroxymethyl-A-nor-5a-steranes by A. verrucosa, no incorporation of tracer from [l-14C]acetate could be demonstrated.355 These results suggest that the unusual nor-sterols in sponge species might arise by modification of dietary sterols. Ring contraction in cholesterol to yield the A-nor-steranes does not result in the elimination of C-4 of the substrate, nor does this carbon form the 3/3-hydroxymethyl group of the product. 

C6C2 monomeric compounds, corresponding to peaks 7 and 9, originate from a minor reaction pathway via elimination of the y-hydroxymethyl group similar to the minor degradation pathway identified in acidolysis (Lundquist... 

As shown by thioacidolysis of coniferyl alcohol, compounds 22 and 23 are formed from coniferyl alcohol end groups. They are recovered in larger amounts, relative to compound pair 11, from kraft lignin than from than from milled wood lignin. Compound 24 originates from Q.C-, alkyl aryl ether structures with a-carbonyl substituents via elimination of the Cy hydroxymethyl group (Lapierre 1986, Lapierre et al. 1987). 

Elemental analyses of the polyformals agreed with or were reasonably close to the calculated values therefore, the polymers contained substantially no poly-(methylene oxide) in the chains. Since excess formaldehyde was used in preparing the prepolymers, presumably their chains were terminated with hydroxymethyl groups. Both water and formaldehyde must then be eliminated during the buildup of polymers ... 

A number of elimination reactions have been reported for drugs including the elimination of the hydroxymethyl group from trimelamol (51), and the iodine from levoihyroxine (52). Perhaps the most common elimination reaction is decarboxylation which has been reported for drugs such as etodolac (53) and foscamet (54). 

Enamines. In a synthesis of 19/3-norsteroids, Habermehl and Haaf1 found that the 19 -hydroxymethyl group of (1) is eliminated as formaldehyde on formation of the enamine (2). Thus, when (1) is heated to reflux with pyrrolidine in methanol, the enamine (2) separates within minutes. The enamine is hydrolyzed to the A4-3-ketone (3) by treatment with sodium acetate in acetic acid-methanol. Such an elimination had been observed previously by retroaldol... 

Other elimination reactions have been reported for various drug substances, as shown in Scheme 43. Trimelamol eliminates its hydroxymethyl groups and forms formaldehyde.171 Levothyroxine eliminates iodine. 172 ADD-17014, a derivative of triazoline, eliminates nitrogen and forms a derivative of aziridine.173 Ditiocarb eliminates carbon disulfide.174... 

Elimination of angular hydroxymethyl groups with formation of enamines Ketones from enamines... 

---