NHC-catalyzed cleavage of vicinal diketones and triketones followed by insertion of enones and ynones

• Ken Takaki,
• Makoto Hino,
• Akira Ohno,
• Kimihiro Komeyama,
• Hiroto Yoshida and
• Hiroshi Fukuoka

Beilstein J. Org. Chem. 2017, 13, 1816–1822, doi:10.3762/bjoc.13.176

• ), tribenzoylethylene (4aa) was formed in 64% yield (Table 1, entry 1). Fortunately possible propargylic alcohols by cross-benzoin reaction were not detected [19]. The other products of 4 were obtained as inseparable mixtures of E- and Z-isomer, except for 4ae and 4ar, but their stereochemistry could not be determined

Electron-transfer-initiated benzoin- and Stetter-like reactions in packed-bed reactors for process intensification

• Anna Zaghi,
• Daniele Ragno,
• Graziano Di Carmine,
• Carmela De Risi,
• Olga Bortolini,
• Pier Paolo Giovannini,
• Giancarlo Fantin and
• Alessandro Massi

Beilstein J. Org. Chem. 2016, 12, 2719–2730, doi:10.3762/bjoc.12.268

• examples, α-hydroxy ketones (benzoin reaction) and 1,4-diketones (Stetter reaction) [1][2][3][4]. The synthetic utility of the umpolung methodology has therefore spurred intensive research on process intensification through the heterogeneization of NHC catalysts [5][6][7][8][9] for facilitating the post

Correction: Recent advances in N-heterocyclic carbene (NHC)-catalysed benzoin reactions

• Rajeev S. Menon,
• Akkattu T. Biju and
• Vijay Nair

Beilstein J. Org. Chem. 2016, 12, 2124–2124, doi:10.3762/bjoc.12.201

• Interdisciplinary Science and Technology,Trivandrum 695 019, India.; Fax: +91 471 2491712; Tel: +91 471 2490406 10.3762/bjoc.12.201 Keywords: acyloin reaction; benzoin reaction; N-heterocyclic carbenes; organocatalysis; umpolung; On page 446, column 2, the sentence “Inoue and co-workers found that it promotes

Recent advances in N-heterocyclic carbene (NHC)-catalysed benzoin reactions

• Rajeev S. Menon,
• Akkattu T. Biju and
• Vijay Nair

Beilstein J. Org. Chem. 2016, 12, 444–461, doi:10.3762/bjoc.12.47

• Interdisciplinary Science and Technology,Trivandrum 695 019, India.; Fax: +91 471 2491712; Tel: +91 471 2490406 10.3762/bjoc.12.47 Abstract N-Heterocyclic carbenes (NHCs) have emerged as a powerful class of organocatalysts that mediate a variety of organic transformations. The Benzoin reaction constitutes one of

• ; benzoin reaction; N-heterocyclic carbenes; organocatalysis; umpolung; Introduction The benzoin reaction (or condensation) is named after the product it furnishes via a catalytic assembly of two molecules of aromatic aldehydes. One molecule of the aldehyde functions as an acyl anion and the other as a

• as homo-benzoin reaction and that of two different aldehydes is known as crossed benzoin reaction. Mechanistically the reaction involves polarity reversal (umpolung) of one aldehyde to generate an acyl anion equivalent and this event is mediated by the catalyst. Alkali metal cyanides and N

N-Heterocyclic carbene-catalyzed direct cross-aza-benzoin reaction: Efficient synthesis of α-amino-β-keto esters

• Takuya Uno,
• Yusuke Kobayashi and
• Yoshiji Takemoto

Beilstein J. Org. Chem. 2012, 8, 1499–1504, doi:10.3762/bjoc.8.169

• including C–C bond construction, that is, formal addition of acyl anion equivalents generated from aldehydes 1 with NHCs, to α-imino esters 2 (Figure 1, (f)). Although a large number of NHC-catalyzed umpolung reactions, such as the benzoin reaction and Stetter reaction, have been developed [24][25][26][27

• protecting groups of the nitrogen atom of α-imino esters 2, which have been known to be excellent electrophiles, would suppress an unexpected reaction of 2 with NHCs, enabling the direct use of 2 as acyl anion acceptors in the cross-aza-benzoin reaction. In this communication, we describe a new, efficient

• , and atom-economical synthesis of the α-amino-β-keto esters by NHC-catalyzed cross-aza-benzoin reaction of aldehydes with α-imino esters under mild basic conditions. Results and Discussion First we initiated the cross-aza-benzoin reaction of benzaldehyde (1a) by employing 20 mol % of commercially

Lithium phosphonate umpolung catalysts: Do fluoro substituents increase the catalytic activity?

• Anca Gliga,
• Bernd Goldfuss and
• Jörg M. Neudörfl

Beilstein J. Org. Chem. 2011, 7, 1189–1197, doi:10.3762/bjoc.7.138

• ; lithium phosphonates; umpolung; Introduction Since the discovery of the cyanide catalyzed benzoin reaction by Liebig and Wöhler in 1832 [1], acyloin-type reactions evolved as powerful tools for couplings of acylanion equivalents with carbon electrophiles. In addition to cyanide [2][3][4][5] and

• (14.3 Hz) (Figure 3). A crystal structure was obtained for phosphonate 15, which shows the (M)-(R,S) diastereomers (Figure 4). The lithium phosphonate catalyzed benzoin reaction (Scheme 5) with phosphonates 9–15 as precatalysts led to the benzoin product in low to moderate yields (5–44%) (Figure 5). The