Diastereoselective synthesis of nitroso acetals from (S,E)-γ-aminated nitroalkenes via multicomponent [4 + 2]/[3 + 2] cycloadditions promoted by LiCl or LiClO₄

• Leandro Lara de Carvalho,
• Robert Alan Burrow and
• Vera Lúcia Patrocinio Pereira

Beilstein J. Org. Chem. 2013, 9, 838–845, doi:10.3762/bjoc.9.96

• as 3 (R2 = alkyl) were employed in various synthetic transformations [6][7] (Scheme 1). In addition, Denmark’s group and others investigated the tandem [4 + 2]/[3 + 2] nitroalkene cycloaddition employing unactivated olefins or enol ethers as dienophiles and electron-deficient alkenes as 1,3

• -dipolarophiles to furnish nitroso acetals of type 4 in an inter- or intramolecular fashion [1][2][3][8][9]. These nitroso acetals can be transformed into functionalized pyrrolizidin-3-ones and in sequence into alkaloid nuclei [1][3][10][11]. The majority of the tandem nitroalkene cycloadditions require the

• addition of a Lewis acid as a promoter reaction; however, a limited number of these species have been employed in these reactions, e.g., SnCl4 or Ti(O-iPr)2Cl2 [1][2][3]. However, LiClO4 or LiCl solutions have not been used in tandem nitroalkene cycloadditions, although they are widely employed as

Mechanochemistry assisted asymmetric organocatalysis: A sustainable approach

• Pankaj Chauhan and
• Swapandeep Singh Chimni

Beilstein J. Org. Chem. 2012, 8, 2132–2141, doi:10.3762/bjoc.8.240

• traditional stirring proceeds at a slower reaction rate as compared to ball-milling [47]. The transition state (TS 4) for this transformation involves a hydrogen-bonded ternary complex of catalyst and substrates in which two NH groups of the squaramide moiety activate the nitroalkene and the quinuclidine

• nitrogen activates and orients the dicarbonyl compounds to provide the Michael adduct in high enantioselectivity. Application of grinding with pestle and mortar for highly stereoselective Michael addition of trisubstituted β-ketoesters to nitroalkene derivatives was reported by Chimni’s group (Scheme 8

• mixing of the catalyst and substrates and also provides additional mechanical pressure. The proposed transition state (TS 5) involves a hydrogen-bonded ternary complex of substrates and catalyst, in which the aromatic hydroxy group activates the nitro group of nitroalkene while the tertiary amine of the

Enantioselective Michael addition of 2-hydroxy-1,4-naphthoquinones to nitroalkenes catalyzed by binaphthyl-derived organocatalysts

• Saet Byeol Woo and
• Dae Young Kim

Beilstein J. Org. Chem. 2012, 8, 699–704, doi:10.3762/bjoc.8.78

• nitroalkenes 2i and 2j provided products with high selectivity (93–99% ee, Table 2, entries 9 and 10). The β-alkyl-substituted nitroalkene, 4-methyl-1-nitropent-1-ene (2k), was also an acceptable starting material and provided the corresponding Michael adducts in high yield and excellent enantioeselectivity

• catalyst III (1.3 mg, 0.002 mmol) in THF (0.4 mL) was stirred at room temperature for 5 min. A solution of nitroalkene 2 (0.2 mmol) was added. The reaction mixture was stirred for 2–5 h at room temperature. After completion of the reaction, the resulting solution was concentrated in vacuo and the obtained