Benzoic acid esters
Bz-OR, Benzoate ester, Benzoate
T. W. Green, P. G. M. Wuts,
Protective Groups in Organic
Synthesis,
Wiley-Interscience, New York, 1999, 173-178, 712-715.
Stability
| H2O: | pH < 1, 100°C | pH = 1, RT | pH = 4, RT | pH = 9, RT | pH = 12, RT | pH > 12, 100°C |
| Bases: | LDA | NEt3, Py | t-BuOK | Others: | DCC | SOCl2 |
| Nucleophiles: | RLi | RMgX | RCuLi | Enolates | NH3, RNH2 | NaOCH3 |
| Electrophiles: | RCOCl | RCHO | CH3I | Others: | :CCl2 | Bu3SnH |
| Reduction: | H2 / Ni | H2 / Rh | Zn / HCl | Na / NH3 | LiAlH4 | NaBH4 |
| Oxidation: | KMnO4 | OsO4 | CrO3 / Py | RCOOOH | I2, Br2, Cl2 | MnO2 / CH2Cl2 |
Protection
4-(N,N-Dimethylamino)pyridine hydrochloride (DMAP·HCl) was used as a
recyclable catalyst for the acylation of inert alcohols and phenols under
base-free conditions. The catalyst can be reused more than eight times without
loss in activity and works with various acylating reagents.
Z. Liu, Y. Liu, Q. Wang, Org. Lett., 2014,
16, 236-239.
A very fast acylation of alcohols with benzoyl chloride in the presence of TMEDA
at -78°C afforded the corresponding benzoates in excellent yields.
T. Sano, Synthesis,
1999,
1141-1144.
Carbonylimidazole derivatives are highly active acylation reagents for
esterification and amidation in the presence of pyridinium salts as catalysts.
These reactions are thought to involve both Brønsted acid and nucleophilic
catalysis. This mode of activation has been applied to the synthesis of
difficult to access oxazolidinones, as well as esters and amides.
S. T. Heller, T. Fu, R. Sarpong, Org. Lett., 2012,
14, 1970-1973.
The use of diacyl disulfide as an acylation reagent enables an efficient ester
formation under DMAP catalysis. A site-selective acylation of phenolic and
primary aliphatic hydroxyl groups greatly expands the scope of protecting group
chemistry. Diacyl disulfides offer excellent moisture tolerance, high efficiency,
and potential in synthetic chemistry and biologically meaningful natural product
modification.
H.-X. Liu, Y.-Q. Dang, Y.-F. Yuan, Z.-F. Xu, S.-X. Qiu, H.-B. Tan, Org. Lett.,
2016, 18, 5584-5587.
Reversible covalent interactions of organoboron compounds enable a
regioselective borinic acid-catalyzed acylation of polyols. This catalytic
protocol enables differentiation of the secondary OH groups of a wide range of
carbohydrate derivatives with diverse acid chloride and chloroformate reagents,
using a structurally simple diarylborinic acid-derived catalyst.
D. Lee, M. S. Taylor, J. Am. Chem. Soc., 2011,
133, 3724-3727.
Highly regioselective monoprotection of hydroxyl groups in sugars was accomplished along with high chemical
yield in the presence of dimethyltin dichloride as catalyst. The regioselectivity of the
benzoylation of sugars is based on a stereorelationship among their hydroxyl groups.
Y. Demizu, Y. Kubo, H. Miyosho, T. Maki, Y. Matusumura, N. Moriyama, O. Onomura, Org. Lett.,
2008,
10, 5075-5077.
Other Syntheses of benzoyl-protected Hydroxyl Groups
A Cu/2,2′-biquinoline catalyst mediates a benzylic C-H esterification with
limiting C-H substrate. Blue-light irradiation promotes carboxylate-to-copper
charge transfer, reducing resting-state CuII to CuI, which
activates the peroxide to generate an alkoxyl radical hydrogen-atom-transfer
species. This "photochemical redox buffering" sustains the activity of Cu
catalysts in radical-relay reactions.
D. L. Golden, C. Zhang, S.-J. Chen, A. Vasilopoulos, I. A. Guzei, S. S. Stahl, J. Am. Chem. Soc.,
2023, 145, 9434-9440.
A very efficient and highly regioselective ring-opening reaction of epoxides
with benzoic acid and its derivatives in the presence of cat. amount of
tetrabutylammonium bromide (TBAB) in anhydrous acetonitrile gave selectively
protected diols.
A. Khalafi-Nezhad, M. N. Soltani Rad, A. Khoshnood, Synthesis,
2003, 2552-2558.
An enantioselective Ni-catalyzed reaction of an alkyl halide (derived from an
aldehyde and an acyl bromide), an olefin, and a hydrosilane provides esters of
chiral dialkyl carbinols. The method is versatile and tolerates substituents
that vary in size and that bear a range of functional groups. A four-component
variant of this process, wherein the alkyl halide is generated in situ, is also
reported.
Z.-P. Yang, G. C. Fu, J. Am. Chem. Soc.,
2020, 142, 5870-5875.
Deprotection
The combination of Co(OAc)2 with a chiral
phosphine-amido-oxazoline (PAO) ligand catalyzes a mild and efficient asymmetric
hydrosilylation of α-oxygenated ketones to provide synthetically useful 1,2-diol
derivatives. The optically enriched products can be converted into chiral
α-hydroxy acids, 1,3-dioxolan-2-ones, ethylene oxides, and 1,2,3-1H-triazoles.
H. Wen, Y. Chen, L. Shi, J. Chen, Y. Luo, Y. Xia, Org. Lett., 2023, 25,
2184-2189.
Acyloxymethyl radicals, that add to imines, were generated from the
corresponding iodomethyl esters by the action of dimethylzinc or triethylborane.
A facile hydrolysis of the acyloxy moiety of the adducts gave the corresponding
amino alcohols in good yield.
K.-i. Yamada, M. Nakano, M. Maekawa, T. Akindele, K. Tomioka, Org. Lett.,
2008,
10, 3805-3808.
The reaction of different esters, thioesters and amides derived from pivalic,
benzoic and 4-tert-butylbenzoic acids with an excess of lithium and a
catalytic amount of naphthalene led, after methanolysis, to the corresponding
alcohols, thiols and amines, respectively, through a reductive non-hydrolytic
procedure.
C. Behloul, D. Guijarro, M. Yus,
Synthesis, 2006, 309-314.
