And acetal hydrolysis

This reaction is simply the reverse of the reaction by which acetals are formed—acetal formation is favored by excess alcohol acetal hydrolysis by excess water Acetal for matron and acetal hydrolysis share the same mechanistic pathway but travel along that pathway m opposite directions In the following section you 11 see a clever way m which acetal formation and hydrolysis have been applied to synthetic organic chemistry... 

Flynn et al. described the synthesis of thiophene-containing analogs of CA-4, 7 [70]. The synthesis of compound 142 was performed using intermediate 96 (a description of the formation of this intermediate is given in Scheme 23). Aromatization of 96 with DDQ and acetate hydrolysis yielded the hydroxyl intermediate 143. Dilithiation of 143 and reaction with 3,4,5-... 

Step 4c Protonation of the lithium carboxylate and acetal hydrolysis. 

Figure III-21 Characterization of maltose by mild oxidation followed by exhaustive methylation and acetal hydrolysis.

Aldopentoses such as D-ribose and L-lyxose have been prepared applying the methodology reported by Enders and co-workers [141,142,143], followed by stereoselective reduction and acetal hydrolysis (O Scheme 21). 

Since the discovery of the illudane-type sesquiterpenoids, a number of related compounds have been isolated, viz., illudalic acid (167), illudinine (168), and dihydroilludin S (169, R = a-OH). The absolute stereochemistry of illudin S (169, R = =0) has been determined. A sequel to the successful stereospecific synthesis of illudin M (170) has been reported by Matsumoto et in which the diacetate (171, R = Ac), which had previously been prepared in the first synthesis, was selectively hydrolysed to the monoacetate (171, R = H). This compound was converted in three steps to the diacetate (172), which, after another selective hydrolysis, Jones oxidation, and acetate hydrolysis, yielded illudin M (170). 

The diversity associated with silyl protecting groups as well as the chemical conditions available for their removal makes them attractive alternatives to benzyl protection of the hydroxy groups of either D- or L-tartaric acid derivatives. O-isopropylidene-L-threitol (37) is mono-protected with er -butyldimethylsilyl chloride to furnish 266, which is converted in three steps to the nitrile 267. Reduction with DIBAL and Wittig olefination followed by desilylation with fluoride and Swern oxidation of the resulting alcohol provides aldehyde 268, which reacts with methyl 10-(triphenylphosphorane)-9-oxo-decanoate (269) to afford enone 270. Reduction of 270 with subsequent preparative TLC and acetal hydrolysis furnishes (9R)-271 and (9 S)-272, both interesting unsaturated trihydroxy Cig fatty acid metabolites isolated from vegetables [91] (Scheme 62). 

A similar synthetic sequence on the enantiomer 226S provided 227S. Oxidation, phosphonate formation [135], and acetal hydrolysis provided enone phosphonate 230. Condensation with the racemic dienal 231 yielded diastereomeric tetraenes 232, which corresponded to the C12-C25 fragment of pimaricin 54. 

D-Glucono-1,4-lactone derivative 14 was converted to L-gulose by reductive opening, followed by persilylation and acetal hydrolysis to give diol 15, then primary oxidation and deprotection. Acetal hydrolysis in the presence of silyl... 

Competitive Neutralization and Acetal Hydrolysis In this method, HCl is fed to a... 

Now that we have seen examples of hydrolytic reactions and acetal hydrolysis by enzymes, we may wonder how important the stereochemistry of the products and reactants is in these transformations. 

Similarly, a benzyUdene acetal linkage as in 128 could be produced via a DDQ-mediated oxidation of the p-methoxybenzyl group in 126 in the presence of the fucose derivative 127 (Scheme 33) [62], a strategy introduced in O-glycosylations by Ito and Ogawa [63]. Subsequent radical cyclization and acetal hydrolysis afforded the a-L-Fuc(l-2)-D-Glc analog 129 in good (60%) yield. 

Maruoka and coworkers [65] also reported the total synthesis of (+) mono-morine (127) using a phase-transfer-catalyzed conjugate addition of glycine ester 128 to Michael acceptor 129 as an early key step in the synthesis sequence. Monomorine (127) is a bicyclic amine, known to be the trail pheromone of Monomorium pharanois [66]. The conjugate addition product 131 was subjected to an intramolecular reductive amination and acetal hydrolysis in one pot reaction with Hantzsch ester 132 and trifluoroacetic acid in aqueous... 

---