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.
Pd catalysis enables a highly efficient and simple method for masking a broad
range of carbonyl groups as acetals and ketals in excellent yields. This
protocol is mild and proceeds with a very low catalyst loading at ambient
temperature.
E. A. Mensah, S. D. Green, J. West, T. Kindoll, B. Lazaro-Martinez, Synlett, 2019,
30,
1810-1814.
Using a photochemical method for acetalization of aldehydes under low-energy
visible light irradiation, a broad range of aromatic, heteroaromatic, and
aliphatic aldehydes have been protected under neutral conditions in good to
excellent yields using a catalytic amount of Eosin Y as the photocatalyst. Even
challenging acid-sensitive aldehydes and sterically hindered aldehydes can be
converted, while ketones remain intact.
H. Yi, L. Niu, S. Wang, T. Liu, A. K. Singh, A. Lei, Org. Lett.,
2017, 19, 122-125.
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.
A perfluorophenyl substituted 1,1′-bi-2-naphthol (BINOL) is an effective photoacid catalyst for promoting the acetalization of enol ethers
with alcohols under irradiation with visible light. The reactions proceed
efficiently with a wide range of substrates under mild and near neutral conditions.
H. Liu, Y. Chen, D. An, X. Zhang, S. Liao, Synlett, 2022,
33,
800-804.
A Pd-catalyzed asymmetric intermolecular hydroalkoxylation of allenes with
phenol as a pronucleophile gives acyclic O,O-acetals in high yields with
very good enantiomeric excesses.
L. Jiang, T. Jia, M. Wang, J. Liao, P. Cao, Org. Lett.,
2015,
17, 1070-1073.
The combination of electrochemical and organoselenium-catalyzed processes
enables an unprecedented synthesis of α-keto acetals from readily available
terminal alkynes and alcohols. The desired products are obtained in a single
operation at room temperature in the absence of basic or metallic additives.
D. Ding, L. Xu, Y. Wei, J. Org. Chem., 2022, 87,
4912-4917.
Chalcone epoxides form α,α-dimethoxyacetophenones on heating with iodine in
methanol through C-C bond cleavage followed by acetalization of the formyl group.
The process occurs through ring opening of the chalcone epoxide by methanol to
form β-methoxy alcohol, cleavage of the C-C bond in the latter to form
α-ketoaldehyde, and acetalization of the formyl group to give the product.
B. G. Jadhav, S. D. Samant,
Synlett, 2014, 25, 1591-1595.
In situ generated hypoiodite catalyzes an oxidative rearrangement of
chalcones under mild and metal-free conditions. This environmental-benign
protocol avoids the use of rare or toxic metals.
M. Zheng, C. Huang, J.-Z. Yan, S.-L. Xie, S.-J. Ke, H.-D. Xia, Y.-N. Duan, J. Org. Chem., 2023, 88,
1504-1514.
A mild and efficient method enables the formation of methylene acetals from 1,2-
and 1,3-diols using methoxymethylphenylsulfide,
1,3-dibromo-5,5-dimethylhydantoin (DBDMH), and dibutylhydroxytoluene (BHT). The
use of BHT suppresses side reactions and enables high-yielding formation of
methylene acetals of various diols, including carbohydrate-type substrates.
T. Maegawa, Y. Koutani, K. Otake, H. Fujioka,
J. Org. Chem.,
2013,
78, 3384-3390.
Nitrosyl tetrafluoroborate (NOBF4) promoted activation of glycosyl
trichloroacetimidate derivatives enables an efficient stereoselective
glycosylation. A series of mono- and disaccharide derivatives were synthesized
in excellent yield and high stereoselectivity at the glycosylation center.
A. Sau, A. Santra, A. K. Misra, Synlett, 2012, 23,
2341-2348.
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.
A gold-catalyzed synthesis of unsaturated spiroketals is regulated by an
acetonide protecting group which undergoes extrusion of acetone to deliver the
desired spiroketals in good yields and diastereoselectivities. The reaction,
which is carried out under very mild conditions employing AuCl as the catalyst,
should be widely applicable.
P. H. S. Paioti, J. M. Ketcham, A. Aponick, Org. Lett.,
2014,
16, 5320-5323.
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.