Reactions hydroxymethyl

Pterin, 5-formyl-6,7-dimethyl-5,6,7,8-tetrahydro-structure, 3, 281 Pterin, 6-hydroxymethyl-reactions, 3, 304 structure, 3, 273 Pterin, 7-hydroxymethyl-synthesis, 3, 311... 

S. Kobayashi, Lanthanide Trifluoromethanesulfonates as Stable Lewis Acids in Aqueous Media. Yb(OTf)3 Catalyzed Hydroxymethylation Reaction of Silyl Enol Ethers with Commercial Formaldehyde Solution Chem Lett. 1991, 2187-2190. 

Bismuth triflate has been reported by Dubac as an efficient catalyst for the Mukaiyama aldol reaction with silyl enol ethers [27] and was recently used with a chiral ligand, as reported by Kobayashi in an elegant hydroxymethylation reaction... 

Lignin was obtained from an industrial soda bagasse spent liquor as before (5). The lignin was initially evaluated as a thermosetting adhesive by the beech strip test. Prior to its application as adhesive, the lignin was reacted with formaldehyde in alkali at temperatures below 60 °C to afford a hydroxymethylated lignin (fi). The hydroxymethylation reaction was done at pH 12 and 13, and samples of the reaction mixtures were evaluated on beech strips with overlaps of 25 x 25 mm, cured for 4 hours at 90 °C and 12% equilibrium moisture content. 

The hydroxymethylation reaction was carried out under several time-temperature conditions using different mole ratios of reactants in a search for conditions that would maximize the extent of hydroxymethylation. The hydroxymethy-lated lignin (HML) reaction product was then evaluated for its ability to form... 

The novalac phenolic resins react under weakly acidic and anhydrous conditions using metal catalysts of the divalent state, e.g. Ca, Mg, Zn, Pb, Cd, Co, Ni and Cu acetals, halides or sulphonates. The mechanism of this ortho-hydroxymethylation reaction has been attributed to the formation of chelate complexes as intermediates as proposed occurs at the initial and subsequent condensation reaction of the phenolic alcoholics. It has been shown that electropositive bivalent metals work best when pH is between 4 and 7. This may be described as follows ... 

Attack of the chlorine atom either towards the methyl side or the hydroxyl side of CH3OH leads to the formation of a loose molecular complex, MC3. This intermediate complex is a key structure in the reaction mechanism and may yield both the hydroxymethyl and methoxy channel products. The next elementary step for the hydroxymethyl reaction channel is the isomerization of MC3 through TS2 (with a very low energy barrier of below 0.5 kJ mol"1) to the... 

A theoretical analysis of the reaction kinetics was given in the study by Jodkowski et a/.31 A hydrogen-bonded molecular complex was found for the hydroxymethyl reaction channel. The formation of this complex may be a ratedetermining process in the two-step reaction mechanism of the H-abstraction from methyl group. On the other hand, the reaction channel which produces methoxy radicals is a simple metathesis reaction. The profile of the potential energy surface obtained by Jodkowski et al at the G2 level is shown in Fig. 14. 

The purified enzyme requires a methylene tetrahydrofolate cofactor [162]. The hydroxymethylation reaction proceeds with inversion [163] (Fig. 33) and probably occurs by a mechanism analogous to serine hydroxymethyl transferase [48]. 

About one tenth of the total amount of vitamin E produced is semi-synthetic, isomerically pure (2R,4 K,8 R)-a-tocopherol (RRR-3) which is used almost exclusively in human applications (mainly pharma). This product, originating from natural sources, is obtained from soya deodorizer distillates (SDD). Vegetable oils refined on a large scale are the major sources of vitamin E compounds [26-28]. The deodorizer distillate, originally a waste stream, contains considerable amounts (up to 10%) of a-, [I-, y- and b-tocopherols (RRR-3 to RRR-6) which are isolated by several separation methods. To increase the value of the vitamin E concentrate of mixed tocopherols obtained from SDD, the lower (I-, y- and d-homologues (RRR-4 to RRR-6, content ca. 90%) have to be transformed subsequently into the biologically more active a-tocopherol (RRR-3, only ca. 5% in the original mixture) by permethylation reactions. Permethylations are performed by chloro-, amino-, or hydroxymethylation reactions to provide functionalized alkylated intermediates, which are reductively converted into RRR-3 (Fig. 3) [29]. 

Figure 16. Examples of 3-hydroxymethyl reactions of 4-carboxyl esterified cephalosporin derivatives.

Formaldehyde is a versatile reagent as one of the most highly reactive Q electrophiles in organic synthesis [9, 10] and dry gaseous formaldehyde has been required for many reactions. For example, the titanium tetrachloride (TiCl4)-promoted hydroxymethylation reaction of a silyl enol ether was carried out by using tri-oxane as an HCHO source under strictly anhydrous conditions [11, 12]. Formalde-hyde/water solution could not be used because TiCl4 and the silyl enol ether reacted with water rather than with HCHO in that aqueous solution. 

It was found that the hydroxymethylation reaction of silyl enol ethers with commercial formaldehyde solution proceeded smoothly when lanthanide triflates were used as Lewis acid catalysis (Eq. 1) [7, 13]. The reactions were first carried out in commercial formaldehyde solution THF media. 

---