Chiral Bifunctional Amine-Squaramide-Catalyzed Highly Diastereo- and Enantioselective Michael/Aldol Cascade Reaction of 2-Mercaptobenzaldehyde and α,β-Unsaturated 7-Azaindoline Amides

Construction of thioglycoside bonds via an asymmetric organocatalyzed sulfa-Michael/aldol reaction: access to 4'-thionucleosides

Thioglycoside bond formation via an asymmetric sulfa-Michael/aldol reaction of (E)-β-nucleobase acrylketones and 1,4-dithiane-2,5-diol has been achieved with a cinchona alkaloid-derived bifunctional squaramide chiral catalyst. Diverse purine, benzimidazole, and imidazole substrates are well tolerated and generate 4'-thionucleoside derivatives containing three contiguous stereogenic centers with excellent results (30 examples, up to 97% yield, >20 : 1 dr and up to 99% ee). Moreover, the novel strategy provides an efficient and convenient synthetic route to construct chiral 4'-thionucleosides.

CPA-catalyzed asymmetric domino thia-Michael/aldol reactions for simultaneous chiral center and axial chirality formation

A highly enantio- and diastereoselective domino thia-Michael/aldol reaction applying 5H-dibenzo[a,c][7]annulen-5-one as a Michael acceptor, catalyzed by a chiral phosphoric acid (CPA), has been developed. The bridged biaryl adduct contains multiple stereogenic centers in the bridging linkage as well as a thermodynamically controlled stereogenic axis. The energy difference between the two atropodiastereomers is about 9.1 kcal mol-1, which accounts for the observed excellent diastereoselectivity (>20 : 1).

Recent Advances in Organocatalyzed Asymmetric sulfa-Michael Addition Triggered Cascade Reactions

The sulfa-Michael addition reaction is a crucial subset of the Michael addition reaction, and aroused the interest of numerous synthetic biologists and chemists. In particular, sulfa-Michael addition triggered cascade reaction has developed quickly in recent years because it offers an efficient method to construct C-S bonds and other bonds in one approach, which is widely applicable for building chiral pharmaceuticals, their intermediates, and natural compounds. This review emphasizes the recent advancements in sulfa-Michael addition-triggered cascade reactions for the stereoselective synthesis of sulfur-containing compounds, including sulfa-Michael/aldol, sulfa-Michael/Henry, sulfa-Michael/Michael, sulfa-Michael/Mannich and some sulfa-Michael triggered multi-step processes. Moreover, some reaction mechanisms and derivatization experiments are introduced appropriately.

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.

Asymmetric synthesis of 9-alkyl tetrahydroxanthenones via tandem asymmetric Michael/cyclization promoted by chiral phosphoric acid

A tandem asymmetric Michael-addition/cyclization of cyclic 1,3-dicarbonyl compounds to β,γ-unsaturated α-ketoesters catalyzed by chiral phosphoric acid is presented. This protocol provides a facile approach for the construction of enantioenriched 9-alkyl tetrahydroxanthenones, an ubiquitous framework found in a number of natural products and pharmaceutical molecules, in high yields with good to high enantioselectivities.

Asymmetric Synthesis of 3-Amine-tetrahydrothiophenes with a Quaternary Stereocenter via Nickel(II)/Trisoxazoline-Catalyzed Sulfa-Michael/Aldol Cascade Reaction: Divergent Access to Chiral Thionucleosides

A generally useful Ni(II)/trisoxazoline-catalyzed asymmetric sulfa-Michael/Aldol cascade reaction is introduced to access chiral 3-amine-tetrahydrothiophene derivatives containing a quaternary stereocenter (32 examples, up to 93% yield, > 20:1 dr and 92% ee). Moreover, the novel strategy offers an efficient and convenient approach to construct chiral thionucleoside analogues.

Organocatalytic enantioselective tandem sulfa-Michael/aldol reaction to access dihydrothiopyran-fused benzosulfolane skeletons bearing three contiguous stereocenters

The first organocatalytic diastereo- and enantioselective tandem sulfa-Michael/aldol reaction of 2-mercaptoindole-3-carbaldehydes and 2-mercaptobenzaldehydes with benzo[b]thiophene sulfones was developed. With multiple hydrogen-bonding thiourea as a catalyst, a wide range of polycyclic dihydrothiopyran-fused benzosulfolanes were smoothly obtained with excellent results (up to 99% yield, >20 : 1 dr and 99% ee) under mild reaction conditions.

Cu(I)-Catalyzed Enantioselective Alkynylation of Thiochromones

A highly efficient asymmetric synthesis of chiral thiochromanones is developed via Cu(I)/phosphoramidite catalyzed asymmetric alkynylation of thiochromones under mild reaction conditions. The catalyst system is tolerant of various thiochromone precursors and terminal alkynes. The established asymmetric transformation provides different enatiomeric-enriched thiochromanones with more molecular complexity and enables access to chiral thioflavanones, a subgroup of flavonoid by further functionalization.