Categories: C-O Bond Formation >
Synthesis of acylals
HBF4-SiO2 is an outstanding catalyst for a convenient, chemoselective, and high-yielding protection of carbonyl compounds as acylals under entirely solvent-free conditions.
V. T. Kamble, B. P. Bandgar, N. S. Joshi, V. S. Jamode, Synlett, 2006, 2719-2722.
Aldehyde 1,1-diacetates are efficiently formed in excellent yields from aldehydes and acetic anhydride under solvent-free conditions at room temperature in the presence of a catalytic amount of copper(II) tetrafluoroborate hydrate.
A. K. Chakraborti, R. Thilagavathi, R. Kumar, Synthesis, 2004, 831-833.
Geminal diacetates and dipivalates were prepared in high yields through a mild and efficient reaction of aldehydes with acetic anhydride or pivalic anhydride using zirconium (IV) chloride as a catalyst under solvent free conditions. Regeneration of aldehydes from the acylals was achieved using the same catalyst in methanol.
G. Smitha, Ch. S. Reddy, Tetrahedron, 2003, 59, 9571-9576.
Various alcohols, phenols, amines and thiols may easily be converted into acetate derivatives by treatment with acetic anhydride in the presence of acetonyltriphenylphosphonium bromide in good yields at room temperature. With the same precatalyst, both aliphatic and aromatic aldehydes can be transformed into the corresponding gem-diacetates under reflux conditions.
A. T. Khan, L. H. Choudry, S. Ghosh, Eur. J. Org. Chem., 2005, 2782-2787.
In the presence of TBAI/TBHP, treatment of esters possessing a methylene carbon α-to oxygen with benzylamines provides bis-esters rather than the expected amides. Under these oxidative conditions, benzylamines generate less nucleophilic carboxylates, which couple at sp3 C-H bonds of esters and cyclic ethers to yield bis-acyl ketals and α-acyloxy ethers, respectively.
G. Majji, S. Rajamanickam, N. Khatun, S. K. Santra, B. K. Patel, J. Org. Chem., 2015, 80, 3440-3446.