Reduction of acetals

Vanillin, being an aldehyde, is able to form acetals and hemiacetals. Therefore, in flavor formulations using high concentrations of vanillin in conjunction with carriers such as propylene glycol, a glc analysis often shows a reduced vanillin peak after storage of the compounded flavor, and the presence of new peaks indicating acetal formation. Addition of about 0.5% of water to the formula reverses the reaction, ie, there is a reduction of acetal, and the reappearance of vanillin peaks. 

Similarly, trimethylsilyl inflate can be used as a catalyst for the alkylation of 2 methoxy 1,3-oxazolidines [104] or 1-acetoxyadamantane [105] with allylsilane and for the reduction of acetals to ethers with trialkylsilanes [106]... 

With TMSOTf 20 as catalyst instead, reduction of acetals or ketals has also been achieved with triethylsilane 84b in the presence of triflic acid/BSA 22a [56] or with triethylsilane 84b/Nafion-H, which can be readily recovered [57]. 

Reduction of Acetals, Ketals, Hemiacetals, Hemiketals, and Orthoesters... 

Table 20. organosilane reduction of acetals, ketals, and hemiketals... 

TABLE 20. ORGANOSILANE REDUCTION OF ACETALS, KETALS, AND HEMIKETALS (Continued)... 

Achim von Armin. Production of a sour smelling product (acetic acid) after dipping the ends of a voltaic pile into beer or wine [3b], cf. also [3a] Faraday reduction of acetic acid... 

The specific rotation of alcohol (R)-3c obtained from UAIH4 reduction of acetate (R)-3b is [alp3 -3.8° (CHCI3, c0.8). 

In addition, though less common, there are cases of preceding chemical reactions (preceding, naturally, the electron transfer). In this case, the reagent Ox is the product of a preliminary chemical reaction of a species that is not itself electroactive. For example, the reduction of acetic acid proceeds through the two microscopic stages ... 

In this connection the reduction of acetic acid to ethanol by Humphreys Glasgow, Davy McKee and BASF must be quoted as an attractive route to ethanol. This route combines the high selectivity of the Monsanto acetic acid process with a hydrogenation step. 

An alternative scheme to simultaneous formation of acetaldehyde and acetic anhydride could entail the carbonylation of methyl acetate to acetic anhydride which is subsequently reduced to acetaldehyde and acetic acid. The reaction of acetaldehyde with excess anhydride would form EDA. In fact, Fenton has described production of EDA by the reduction of acetic anhydride using both rhodium and palladium salts as catalysts when modified with triphenylphosphine (26). Two possible mechanisms for the reduction are postulated in equation 16. 

Reduction of acetals or ortho esters 0-80 Reduction of epoxides 0-92 Cleavage of acetals or ortho esters with Grignard reagents... 

Reaction of halides with oxide ion 0-68 Cleavage of oxonium salts 0-79 Reduction of acetals or ketals 0-92 Reaction between Grignard reagents and acetals or ketals dimerization of acetals... 

D. A. Home and A. Iordan, An efficient reduction of acetals and ketals to methyl ethers, Tetrahedron Lett 1357 (1978). 

Dealkoxylation (see Hydrogenolysis, Reduction of acetals and ketals) Debenzylation (see Reduction reactions) Debromination (see Elimination reactions)... 

Dichloro-2,2-difluoroethylene, 105 (Diethylamino)sulfur trifluoride, 110 Reduction reactions (see also Deoxygenation, Reductive. . . ) of acetals and ketals Dibromoalane, 237 Diisobutylaluminum hydride, 237 Triethylsilane-Tin(IV) chloride, 237 of acetates and other esters to alkanes Nickel boride, 197 Triphenylsilane, 334 of acyl halides to alcohols Sodium cyanoborohydride-Tin(II) chloride, 280... 

Reduction of acetals (if, 8, 454). 4,6-O-Benzylidene-hexopyranosides (1) are reduced by NaBU, ( N and hydrogen chloride in the presence of 3 A molecular sieves lo 6-hen/yl ethers with a free (-hydroxyl group (2).1... 

This interesting methodology broadens the preceding electron transfer reduction of acetates and pivaloates, and seems very efficient for synthesizing protected 2 -deoxy uridine such as 85 in high yields (85 %) (Scheme 44). 

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