Synthesis of acyloins (α-hydroxy carbonyl compounds)
Lanthanum tricyanide efficiently catalyzes a benzoin-type coupling between acyl silanes and ketones. Good yields are obtained over a broad substrate scope encompassing aryl, alkyl, and sterically hindered ketones.
J. C. Tarr, J. S. Johnson, Org. Lett., 2009, 11, 3870-3873.
Operationally simple cyanide-catalyzed silyl benzoin reactions afforded unsymmetrical aryl-, heteroaryl-, and alkyl-substituted silyl ether protected benzoin adducts with complete regiocontrol.
X. Linghu, J. S. Johnson, Angew. Chem. Int. Ed., 2003, 42, 2534-2536.
A hydrogen bond donating substituent to improve enantiocontrol together with an acidifying pentafluorophenyl substituent to enhance catalyst efficiency results in a triazolium ion precatalyst that promotes the asymmetric benzoin condensation with excellent efficiency and unprecedented enantioselectivity.
L. Baragwanath, C. A. Rose, K. Zeitler, S. J. Connon, J. Org. Chem., 2009, 74, 9214-9217.
The development of a triazolium salt as an efficient precatalyst for the asymmetric benzoin condensation is described. The high asymmetric inductions in benzoin condensations are a result of the conformational rigidity of the bicyclic nucleophilic carbene catalyst and the shielding of the Breslow intermediate by the sterically demanding tert-butyl group.
D. Enders, U. Kallfass, Angew. Chem. Int. Ed., 2002, 41, 1743-1745.
The appropriate choice of N-heterocyclic carbene catalysts enables an unprecedented high level of regioselectivities in the intermolecular crossed acyloin condensations of various aromatic aldehydes with acetaldehyde.
M. Y. Jin, S. M. Kim, H. Han, D. H. Ryu, J. W. Yang, Org. Lett., 2011, 13, 880-883.
An operationally simple and mild visible-light, single-electron-transfer (SET), photoredox cross-coupling enables the synthesis of α-alkoxyketones in high yields from various aliphatic and aromatic acyl chlorides and structurally diverse potassium alkoxymethyltrifluoroborates. The bond connection is unique to both alkylboron chemistry and photoredox/Ni catalysis.
J. Amani, E. Sodagar, G. A. Molander, Org. Lett., 2016, 18, 732-735.
A one-pot method allows the synthesis of α-siloxy-Weinreb amides from aldehydes using N,O-dimethylhydroxylamine and a masked acyl cyanide reagent bearing a tert-butyldimethylsilyl group. The TBS group avoids the competitive reaction toward N-methoxy-N-methyl-2-amino-1-siloxymalononitrile.
H. Nemoto, R. Ma, H. Moriguchi, T. Kawamura, M. Kamiya, M. Shibuya, J. Org. Chem., 2007, 72, 9850-9853.
β-Silyloxy-α-keto esters are prepared through a cyanide-catalyzed benzoin-type reaction with silyl glyoxylates and aldehydes. A subsequent dynamic kinetic resolution provides enantioenriched orthogonally protected alcohols, that can be converted to the corresponding β-silyloxy-α-amino esters.
K. M. Steward, J. S. Johnson, Org. Lett., 2010, 12, 2864-2867.
An enantioselective intramolecular crossed-benzoin reaction catalyzed by novel chiral N-heterocyclic carbenes has been developed. A tetracyclic trazolium salt catalyzes the cyclization with generation of a quartenary stereocenter in high yields and excellent enantomeric excess.
D. Enders, O. Niemeier, T. Balensiefer, Angew. Chem. Int. Ed., 2006, 45, 1463-1467.
While 3,4;5,6-di-O-isopropylidene-N-phthaloyl-D-glucosamine propane-1,3-diyl dithioacetal underwent fast β-elimination, the corresponding N-acetyl derivative was easily deprotonated with butyllithium to form the dilithiated intermediate. Stoichiometry and temperature were crucial factors for selective C-C coupling with various electrophiles.
Y.-L. Chen, R. Leguijt, H. Redlich, R. Fröhlich, Synthesis, 2006, 4212-4218.