Catalytic, Asymmetric Synthesis of β-Lactams

N‐Heterocyclic Carbene‐Catalyzed Cyclization of Unsaturated Acyl Chlorides and Ketones

“…

Abstract: A straightforward synthesis of optically active trifluoromethyl dihydropyranones and spirocyclic oxindole-dihydropyranones has been realized by the chiral N-heterocyclic carbenes-catalyzed cy-A C H T U N G T R E N N U N G clization of a,b-unsaturated b-methylacyl chlorides with activated trifluoromethyl ketones or isatin derivatives.Keywords: asymmetric catalysis; cyclization; dihy-A C H T U N G T R E N N U N G dropyranones; N-heterocyclic carbenes; organocatalysis; vinylketenes Since Staudingers discovery of ketenes and the cycloaddition of ketene with imines to form b-lactams in early 1900s, [1] the cycloaddition reactions of ketene have become one of the powerful methodologies for construction of cyclic compounds.[2] In last decades, the catalytic enantioselective [2 + 2] or [2 + 4] cycloaddition of ketenes with aldehydes, [3] imines, [4] azo compounds, [5] nitro compounds, [6] oxadienes, [7] and azadienes [8] had been well established. In 2008 and later, we, [9] independently with Smith et al, [10] have demonstrated that N-heterocyclic carbenes (NHCs) [11] were efficient catalysts for the formal cycloaddition reactions of ketenes.

…”

Organocatalytic Asymmetric Cycloaddition Reaction of Ketenes

“…10 mol% 1c LiClO 4 , EtN(i-Pr) 2 Nelson 等认为该反应的机理是: 现场生成的烯酮在 亲核催化剂和 Lewis 酸作用下首先生成金属配位的烯醇 盐, 烯醇盐再通过一个含有金属离子的六元环状过渡态 与醛进行加成, 最后环化生成 β-内酯(Scheme 9). 六元 环状过渡态的形成, 不仅活化了底物, 而且创造了一个 紧密的手性控制环境, 使得 C-C 键的生成具有很高的 立体选择性.…”

Asymmetric aza‐Henry reaction of N‐tosyl imine

“…[18][19][20][21][22][23][24][25][26] The toluenesulfonyl activating group of imine can be removed easily by treatment with Mg/MeOH, 27,28 treatment with phenol in refluxing HBr/HOAc solution with addition of H 2 O, 29 or treatment with SmI 2 in THF at room temperature. 30 Our group found that the Ln(O i Pr) 3 was a very effective catalyst for the aza-Henry reaction when the N-tosyl imine was used as the substrate (cat., 5 mol %; yield, 99%). 31 But combination La(O i Pr) 3 with a series of chiral ligands such as BINOL, chiral diamines, and chiral aminoalchols as catalysts, all led to low yield and low ee.…”