The nitroaldol (Henry) reaction is an important carbonyl addition process that affords products that may be transformed into valuable building blocks. 1 Therefore, it is not surprising that recent efforts have focused on the development of catalytic enantioselective reaction variants. The current contributions to this area have been highlighted by the recent studies of Shibasaki and Trost. [2][3][4][5] The purpose of this Communication is to report a new catalyst system for the nitroaldol reaction (eqs 1,2; M ) Cu, X ) OAc). The basis for the current study was to identify a weakly Lewis acidic metal complex bearing moderately basic charged ligands (X) that would facilitate the deprotonation of nitroalkanes (eq 1) as a prelude to the aldol addition process (eq 2). It was felt that divalent metal acetate-ligand complexes of the general structure A might meet these requirements because acetate has been employed as a Brønsted base in the racemic nitroaldol reaction. 1 A series of divalent metal acetates in combination with chiral bidentate ligands were screened as enantioselective catalysts for the nitroaldol process. 6,7 From this survey, bis(oxazoline) 8 (box) complexes derived from Cu(OAc) 2 emerged as promising catalyst candidates. The results from the ligand survey with this metal acetate are summarized in Table 1. The five box ligands (1a-d, 2) with the illustrated absolute configurations that were evaluated with Cu(OAc) 2 ‚H 2 O afforded promising levels of enantioselection (entries 1-5). 8,9 In each instance, the reactions carried out at ambient temperature were complete within 24 h. From this comparison, the indabox ligand 2 proved to be the ligand of choice, 9 providing the nitro alcohol product in 74% ee (Table 1, entry 5). With ethanol as the solvent (Table 1, entry 6), the nitro alcohol product was isolated in 81% ee. Further optimization of this process showed that the reaction may be performed with lower catalyst loadings (1-5 mol %), while the use of 10 equiv of nitromethane was found to be sufficient for the reaction to proceed to completion. Reaction concentrations could also be increased to as high as 1.0 M with no change in enantioselectivity. Cu(II) carboxylate structure was also evaluated with ligand 2, and it was concluded that this catalyst variable is subordinate to ligand architecture. 10 In all instances, the only side reaction observed in these reactions was the accompanying dehydration product.With optimized conditions in hand, the scope of the reaction was explored (Table 2). In general, high enantiomeric excesses (87-94% ee) are observed at room temperature for aromatic aldehydes bearing either electron-withdrawing or electron-donating groups (entries 1-9). 11 Aliphatic branched and unbranched aldehydes are also acceptable substrates, affording nitro alcohol adducts in good yields and enantioselectivities (entries 10-15, 90-94% ee).Reaction enantioselectivity can be further improved by lowering the temperature at the accompanying expense of increasing the reaction time. In one insta...

Nickel-catalyzed additions of arylboronic acids to alkynes, followed by enantioselective cyclizations of the alkenylnickel species onto tethered ketones or enones, are reported. These reactions are reliant upon the formal anti-carbonickelation of the alkyne, which is postulated to occur by the reversible E/Z isomerization of an alkenylnickel species.

Nitrogen-containing aromatic heterocycles (azaarenes) are of widespread chemical significance, and chiral compounds containing azaarenes feature prominently in pharmaceuticals, agrochemicals, and natural products. ThisPerspective highlights the use of a relatively underdeveloped strategy to prepare chiral azaarene-containing compounds: exploitation of the C=N bond embedded within certain azaarenes to activate adjacent functionality in catalytic asymmetric reactions. Work in this area has resulted in the development of several different types of catalytic enantioselective processes, including reductions, nucleophilic additions, and reductive couplings. It is hoped that this Perspective will encourage more researchers to work in this promising area.

1,3-Enynes containing allylic hydrogens cis to the alkyne are shown to act as one-carbon partners, rather than two-carbon partners, in various rhodium-catalyzed oxidative annulations. The mechanism of these unexpected transformations is proposed to occur through double C–H activation, involving a hitherto rare example of the 1,4-migration of a RhIII species. This phenomenon is general across a variety of substrates, and provides a diverse range of heterocyclic products.