Michael Addition–Lactonization of Arylacetyl Phosphonate to β,γ-Unsaturated α-Keto Esters for the Synthesis of Chiral syn-3,4-Dihydropyranones and 5,6-Dihydropyranones

Catalytic Asymmetric Synthesis of Chiral Thiohydantoins via Domino Cyclization Reaction of β,γ-Unsaturated α-Ketoester and N,N'-Dialkylthiourea

The first catalytic asymmetric route to synthesize chiral thiohydantoins containing a quaternary stereogenic center has been established utilizing a chiral phosphoric acid-catalyzed domino cyclization reaction of N,N'-dialkyl thioureas with β,γ-unsaturated...

A Novel Dual Organocatalyst for the Asymmetric Pinder Reaction and a Mechanistic Proposal Consistent with the Isoinversion Effect Thereof

In general, the Pinder reaction concerns the reaction between an enolisable anhydride and an aldehyde proceeding initially through a Knoevenagel reaction followed by the ring closing process generating lactones with at least two chiral centers. These scaffolds are frequently present in natural products and synthetic bioactive molecules, hence it has attracted intense interest in organic synthesis and medicinal chemistry, particularly with respect to controlling the diastereo- and enantioselectivity. To the best of our knowledge, there has been only one attempt prior to this work towards the development of a catalytic enantioselective Pinder reaction. In our approach, we designed, synthesized, and tested dual chiral organocatalysts by combining BIMAH amines, (2-(α-(alkyl)methanamine)-1H-benzimidazoles, and a Lewis acid motif, such as squaramides, ureas and thioureas. The optimum catalyst was the derivative of isopropyl BIMAH bearing a bis(3,5-trifluoromethyl) thiourea, which afforded the Pinder products from various aromatic aldehydes with diastereomeric ratio >98:2 and enatioselectivity up to 92 ee%. Interestingly, the enantioselectivity of this catalyzed process is increased at higher concentrations and exhibits an isoinversion effect, namely an inverted "U" shaped dependency with respect to the temperature. Mechanistically, these features, point to a transition state involving an entropy-favored heterodimer interaction between a catalyst/anhydride and a catalyst/aldehyde complex when all other processes leading to this are much faster in comparison above the isoinversion temperature.

Construction of Chiral Isotetronic Acid-Fused Thiochromane via Doubly Annulative Strategy

A sulfa-Michael/aldol/lactonization cascade reaction has been established to construct isotetronic acid-fused thiochromanes in a highly stereoselective fashion (≥11:1 dr, 35-98% ee). The tricyclic products were obtained in 35-99% isolated yields in the presence of a bifunctional squaramide. Three reactive sites of β,γ-unsaturated α-ketoester, including the less-explored ester carbonyl group, were sequentially utilized to construct two fused heterocycles in a one-pot operation.

A AgOAc/quinine-derived aminophosphine complex as an efficient catalyst for diastereo- and enantioselective 1,3-dipolar cycloaddition of α,β-unsaturated 7-azaindoline amides and azomethine ylides

The Dixon’s catalyst system is effective for the asymmetric 1,3-dipolar cycloaddition.

Catalyst-controlled diastereoselectivity reversal in the formation of dihydropyrans

In dihydropyran synthesis, use of (S)-3b is crucial for overcoming the inherent trans-selectivity and obtaining unusual cis-adducts with high enantioselectivity.

An asymmetric organocatalytic vinylogous Mannich reaction of 3-methyl-5-arylfuran-2(3H)-ones with N-(2-pyridinesulfonyl) imines: enantioselective synthesis of δ-amino γ,γ-disubstituted butenolides

A series of δ-amino γ,γ-disubstituted butenolides were obtained with satisfactory results via an asymmetric vinylogous Mannich reaction of 3-methyl-5-arylfuran-2(3H)-ones with N-(2-pyridinesulfonyl)imines.

Multiple Hydrogen-Bonding Bifunctional Thiourea-Catalyzed Asymmetric Dearomative [4 + 2] Annulation of 3-Nitroindoles: Highly Enantioselective Access to Hydrocarbazole Skeletons

A method for the enantioselective construction of hydrocarbazole skeletons through dearomative [4 + 2] annulation of 3-nitroindoles with Nazarov reagents is reported. The reactions use multiple hydrogen-bonding bifunctional thiourea as catalyst and are highly diastereo- and enantioselective (up to >20:1 dr and >99% ee). The protocol was demonstrated by preparative-scale experiment and the versatile conversion of the products. The multiple hydrogen-bonding in the catalyst plays a pivotal role in the reactivity and stereoselectivity.