Categories: C-O Bond Formation, Synthesis of O-Heterocycles >
Synthesis of acetals
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Protecting Groups
Recent Literature
Perchloric acid adsorbed on silica gel is an extremely efficient, inexpensive,
and reusable catalyst for the protection of aldehydes and ketones and the
subsequent deprotection. Acetalization was mostly carried out under solvent-free
conditions with trialkyl orthoformates, but weakly electrophilic carbonyl
compounds and substrates that can coordinate with the catalyst, required the
corresponding alcohol as solvent.
R. Kumar, D. Kumar, A. K. Chakraborti, Synthesis, 2007, 299-303.
Ketone di-sec-alkyl acetals are obtained in very good yields by treatment
of ketones with tri-sec-alkyl orthoformate and the corresponding alcohol
in the presence of a catalytic amount of cerium(III) trifluoromethanesulfonate.
F. Ono, H. Takenaka, Y. Eguchi, M. Endo, T. Sato, Synlett, 2009,
487-489.
Zirconium tetrachloride (ZrCl4) is a highly
efficient and chemoselective catalyst for the acetalization, and in situ
transacetalization of carbonyl compounds under mild reaction conditions.
H. Firouzabadi, N. Iranpoor, B. Karimi, Synlett, 1999, 321-323.
Treatment of symmetrical O,O-acetals with TESOTf and 2,4,6-collidine
formed weakly electrophilic collidinium salts. Subsequent addition of
nucleophiles, such as alcohols, lithium thioxide, and sodium azide, to the salts
afforded the corresponding O,O-mixed, O,S- and N,O-acetals
in good yields.
H. Fujioka, T. Okitsu, T. Ohnaka, R. Li, O. Kubo, K. Okamoto, Y. Sawama, Y. Kita, J. Org. Chem.,
2007,
72, 7898-7902.
0.01 mol-% Zinc(II) salts catalyze the reaction between acetals and acid halides to
provide haloalkyl ethers in near-quantitative yield in 1 - 4 h. The
solutions of haloalkyl ethers can be utilized directly in
reactions in which the presence of the ester byproduct does not interfere.
Excess carcinogenic haloalkyl ether is destroyed on workup.
M. A. Berliner, K. Belecki, J. Org. Chem., 2005,
70, 9618-9621.
Acyclic and cyclic acetals of various carbonyl
compounds were obtained in excellent yields in the presence of trialkyl
orthoformate and a catalytic amount of tetrabutylammonium tribromide in
absolute alcohol. This convenient, mild, chemoselective method allows acetalization of an
aldehyde in the presence of ketone, unsymmetrical acetal formation, and
tolerates acid-sensitive protecting groups.
R. Gopinath, Sk. J. Haque, B. K. Patel, J. Org. Chem.,
2002,
67, 5842-5845.
The use of a chiral Brønsted acid catalyst for the activation of
trichloroacetimidate glycosyl donors influences the stereochemical outcome of
glycosylation processes in toluene, hinting that perhaps diastereocontrol may
become achievable through the judicious use of chiral organic catalysts.
D. J. Cox, M. D. Smith, A. J. Fairbanks, Org. Lett., 2010,
12, 1452-1455.
Use of La(OTf)3 as a Lewis acid promoter for N-iodosuccinimide-mediated
activation of thioglycosides enables a smooth glycosylation reaction with good
to excellent yields and stereoselectivity.
S. Mukherjee, B. Mukhopadhyay, Synlett, 2010,
2853-2856.
A novel microwave-assisted, operationally simple, tandem bis-aldol reaction of
ketone with paraformaldehyde catalyzed by polystyrenesulfonic acid in aqueous
medium delivers 1,3-dioxanes in high yield.
V. Polshettiwar, R. S. Varma, J. Org. Chem.,
2007,
72, 7420-7422.
Hg(II) salts are highly efficient catalysts for a versatile construction of
spiroketals in an instant reaction in high yields at ambient temperature from
alkyne diols or THP-semiprotected alkyne diols in aqueous conditions.
Monounsaturated spiroketals and furans were accessed with equal ease when
propargylic triols (or propargylic diols) were subjected to similar conditions.
K. Ravindar, M. S. Reddy, P. Deslongchamps, Org. Lett., 2011,
13, 3178-3181.
K. Ravindar, M. S. Reddy, P. Deslongchamps, Org. Lett., 2011,
13, 3178-3181.
An intramolecular hydro-O-alkylation of aldehydes leads to spiroketals, bicyclic ketals, and aminals.
Tertiary and sterically hindered secondary sp3 C-H bonds are
transformed into C-O bonds under the action of a catalytic amount of a variety of
Lewis acids. The mechanism probably involves a tandem hydride transfer/cyclization sequence.
S. J. Pastine, D. Sames, Org. Lett.,
2005,
7, 5429-5431.
A cyclization of monopropargylic triols to form olefin-containing spiroketals is
rapid and high yielding in the presence of 2 mol % of a catalyst generated in
situ from Au[P(t-Bu)2(o-biphenyl)]Cl and AgOTf. Various
substituted triols lead to substituted 5- and 6-membered ring spiroketals.
A. Aponick, C.-Y. Li, J. A. Palmes, Org. Lett., 2009,
11, 121-124.
