Categories: C-H Bond Formation >
Reduction of carboxyl compounds to aldehydes
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The combination of an air-stable Ni precatalyst, dimethyl dicarbonate as an
activator, and diphenylsilane as reductant enables a direct conversion of
carboxylic acids to aldehydes for a wide range of substrates in good yields and
with no overreduction to alcohols.
A. V. Iosub, S. Moravčík, C.-K. Wallentin, J. Berman,
Org. Lett., 2019, 21, 7804-7808.
The reduction of tertiary amides to aldehydes via Cp2Zr(H)Cl shows
several distinct advantages: The reaction requires a very short reaction time
and provides very high yields of the aldehydes with good chemoselectivity.
Furthermore, the reaction does not require extensive workup procedures, nor does
it require scrupulously dry conditions. Additionally, substrate dependence is minimal.
J. M. White, A. R. Tunoori, G. I. Georg, J. Am. Chem. Soc., 2000,
122, 11995-11996.
A highly efficient in situ generation of the Schwartz reagent provides a
convenient method for the reduction of amides to aldehydes and the
regioselective hydrozirconation-iodination of alkynes and alkenes. These
single-step processes proceed in very short reaction time, show excellent
functional group compatibility, and use inexpensive and long-storage stable
reducing reagents.
Y. Zhao, V. Snieckus, Org. Lett., 2014,
16, 390-393.
A chemoselective activation of a secondary amide with triflic anhydride in the
presence of 2-fluoropyridine enables a mild reduction using triethylsilane, a
cheap and rather inert reagent. Imines can be isolated after a basic workup or
readily transformed to the aldehydes following an acidic workup. The amine
moiety can be accessed by addition of Hantzsch ester to the reaction mixture.
G. Pelletier, W. S. Bechara, A. B. Charette, J. Am. Chem. Soc., 2010,
132, 12817-12819.
In a sequential one-pot process for the conversion of sterically demanding
N,N-diisopropylamides to aldehydes, amides are activated with EtOTf to form
imidates, which are reduced with LiAlH(OR)3 [R = t-Bu, Et] to
give aldehydes by hydrolysis of the resulting hemiaminals. The non-nucleophilic
base 2,6-DTBMP remarkably improves reaction efficiency. The reaction tolerates
various reducible functional groups, including aldehyde and ketone.
P. Xiao, Z. Tang, K. Wang, H. Chen, Q. Guo, Y. Chu, L. Gao, Z. Song, J. Org. Chem., 2018, 83, 1687-1700.
A palladium-catalyzed reduction of 2-pyridinyl esters using hydrosilanes is
applicable to the preparation of aliphatic, aromatic, and α,β-unsaturated
aldehydes. Various functional groups, such as fluoro, methoxy, aldehyde, acetal,
and ester, are tolerated.
J. Nakanishi, H. Tatamidani, Y. Fukumoto, N. Chatani, Synlett,
2006, 869-872.
The combination of Pd(OAc)2/Et3SiH enables
ligand-controlled non-decarbonylative and decarbonylative conversions of acyl
fluorides. When tricyclohexylphosphine (PCy2) was used as the ligand,
aldehydes were obtained as simple reductive conversion products, whereas
1,2-bis(dicyclohexylphosphino)ethane (Cy2P(CH2)2PCy2,
DCPE) as the ligand favored the formation of hydrocarbons as decarbonylative
reduction products.
Y. Ogiwara, Y. Sakuria, H. Hattori, N. Sakai, Org. Lett.,
2018, 20, 4164-4167.
Re2(CO)10 efficiently catalyzes the direct reduction of
various carboxylic acids under UV irradiation at ambient temperature. While
aliphatic carboxylic acids were readily converted to the corresponding
disilylacetals with low catalyst loading in the presence of Et3SiH,
aromatic analogues required more drastic conditions.
D. Wei, R. Buhaibeh, Y. Canac, J.-B. Sortais,
Org. Lett., 2019, 21, 7713-7716.
Treatment of ethanethiol esters with triethylsilane and palladium on carbon
at ambient temperature furnished aldehydes. In addition, a variety of
ketones has been prepared by a palladium-catalyzed reaction of ethanethiol
esters with organozinc reagents. Both transformations tolerate various
functional groups, including esters, ketones, aromatic halides and
aldehydes.
H. Tokuyama, S. Yokoshima, T. Yamashita, S.-C. Lin, L. Li, T. Fukuyama,
J. Braz. Chem. Soc., 1998, 9, 381-387.
Reduction of ethanethiol esters of α-amino acids to α-amino aldehydes by
triethylsilane and catalytic palladium-on-carbon is described. α-Amino
aldehydes with Boc, Cbz, or Fmoc protection could be obtained without
racemization in high yield.
H. Tokuyama, S. Yokoshima, S.-C. Lin, L. Li, T. Fukuyama, Synthesis,
2002, 1121-1123.
A copper hydride-catalyzed enantioselective reduction of α,β-unsaturated
carboxylic acids provides various saturated β-chiral aldehydes in good yields,
with high levels of enantioselectivity and broad functional group tolerance. A
reaction pathway involving a ketene intermediate is proposed.
Y. Zhou, J. S. Bandar, R. Y. Liu, S. L. Buchwald, J. Am. Chem. Soc., 2018,
140, 606-609.
A copper hydride-catalyzed enantioselective reduction of α,β-unsaturated
carboxylic acids provides various saturated β-chiral aldehydes in good yields,
with high levels of enantioselectivity and broad functional group tolerance. A
reaction pathway involving a ketene intermediate is proposed.
Y. Zhou, J. S. Bandar, R. Y. Liu, S. L. Buchwald, J. Am. Chem. Soc., 2018,
140, 606-609.