Reaction of aldehydes with N-hydroxybenzenesulfonamide. Acetal formation catalyzed by nucleophiles

Method for the Selective Formation of Dimethyl Acetals in the Presence of Hydroxylamine

“…Although Hassner previously reported a related process employing catalytic amounts of N-phenyl hydroxylamine for the preparation of acetals or ketals, [5] our conditions have the potential to be selective for aldehydes in the presence of ketones. As shown in Table 3, a number of aldehydes were treated with 0.1 mol equivalents each of hydroxylamine hydrochloride and sodium hydroxide (powder).…”

“…These results indicate that the catalytic variant of this reaction will be selective for aldehydes in the presence of ketones, which is an improvement over previous hydroxylamine-induced acetalization processes. [4,5] DISCUSSION From the exploration of reaction conditions summarized in Table 2, it appeared that free hydroxylamine was responsible for the clean conversion of aldehydes to dimethyl acetals. Because the nonnucleophilic hydrochloride salt was inefficient in this conversion and base alone resulted in no reaction, it was logical to conclude that the nucleophilic hydroxylamine played a key role in the reaction.…”

Hydroxamic Acids: Chemistry, Bioactivity, and Solutionand Solid‐Phase Synthesis

“…Hassner et al [130] proposed that the mechanism for hydroxamic acid formation may involve nucleophilic attack of the anion of N-hydroxybenzenesulfonamide to give 35, followed by ring closure to give an N-hydroxyaziridine, 36, which would ring open to give the hydroxamic acid (Scheme 3.16, a). Nucleophilic attack of an N-hydroxynitrene, on the aldehydic carbonyl carbon was also suggested as a possible route to 36 (Scheme 3.16, b) …”

“…Synthesis of 4-Chlorobenzohydroxamic Acid [130] O HN Cl OH A 1.93 M sodium methoxide/methanol solution (2.18 ml, 4.2 mmol) was added dropwise with stirring to an ice-cooled solution of N-hydroxybenzenesulfonamide (0.37 g, 2.1 mmol) in methanol. 4-Chlorobenzaldehyde(0.28 g, 2 mmol) dissolved in methanol (2 ml) was added, and the reaction mixture was warmed to room temperature and stirred for an additional 2 h. The solution was concentrated under vacuum, diluted with 100 ml of ether, and extracted twice with 2 M NaOH.…”

Solvent‐switchable Acetalization by Yb(OTf)3‐Catalyzed Procedures

“…A variety of proton or Lewis acids have been used as catalysts to accomplish O,O'-diethyl acetal formation. [5][6][7][8][9][10][11][12][13][14][15] However, most of these procedures often require high temperatures, or a large excess of reagents, or long reaction time, and/or other drastic reaction conditions that generate potentially harmful environment waste. In addition, chemoselectivity is often difficult to achieve in a multi-carbonyl system.…”