Organocatalytic and enantioselective synthesis of beta-(hydroxyalkyl)-gamma-butyrolactones

Organocatalytic aldol approach for the protecting group-free asymmetric synthesis of (7R')-parabenzlactone, (-)-hinokinin, (-)-yatein, (-)-bursehernin, (-)-pluviatolide, (+)-isostegane and allied lignans

A short and efficient catalytic asymmetric protection-free synthesis of dibenzylbutyrolactone lignans, such as (-)-hinokinin, (-)-yatein, (-)-bursehernin, (-)-pluviatolide, and their 7'-hydroxylignans - (7'R)-parabenzlactone, (7'R)-hydroxyyatein, (7'R)-hydroxybursehernin, and (7'R)-hydroxy pluviatolide, respectively, is described. The syntheses of (+)-isostegane and the formal synthesis of (-)-podophyllotoxin and bicubebins are also described. Organocatalytic aldol-reduction-lactonization and Pd/C-catalyzed hydrogenative debromination are two-pot sequential reactions for the enantioselective synthesis of hydroxybutyrolactone 13b with excellent diastereo- and enantioselectivity (dr 33 : 1 and >99% ee). The protecting group-free chemoselective α-alkylation of 13b directly led to 7'-hydroxydibenzylbutyrolactone lignans, followed by hydrogenative dehydroxylation, which led to their (deoxy) dibenzylbutyrolactone lignans, and the syntheses were completed in three to five steps from 6-bromopiperonal.

Catalytic Enantioselective Synthesis of (-)-Podophyllotoxin

The first catalytic enantioselective total synthesis of (-)-podophyllotoxin is accomplished by a challenging organocatalytic cross-aldol Heck cyclization and distal stereocontrolled transfer hydrogenation in five steps from three aldehydes. Reversal of selectivity in hydrogenation led to the syntheses of other stereoisomers from the common precursor.

Catalytic Asymmetric Synthesis of Butenolides and Butyrolactones

γ-Butenolides, γ-butyrolactones, and derivatives, especially in enantiomerically pure form, constitute the structural core of numerous natural products which display an impressive range of biological activities which are important for the development of novel physiological and therapeutic agents. Furthermore, optically active γ-butenolides and γ-butyrolactones serve also as a prominent class of chiral building blocks for the synthesis of diverse biological active compounds and complex molecules. Taking into account the varying biological activity profiles and wide-ranging structural diversity of the optically active γ-butenolide or γ-butyrolactone structure, the development of asymmetric synthetic strategies for assembling such challenging scaffolds has attracted major attention from synthetic chemists in the past decade. This review offers an overview of the different enantioselective synthesis of γ-butenolides and γ-butyrolactones which employ catalytic amounts of metal complexes or organocatalysts, with emphasis focused on the mechanistic issues that account for the observed stereocontrol of the representative reactions, as well as practical applications and synthetic potentials.

Proline Sulfonamide-Based Organocatalysis: Better Late than Never

The history of proline sulfonamides for use in catalyzing highly enantioselective and diastereoselective C-C bond forming reactions is described. Highlighted is the development of N-(p-dodecylphenylsulfonyl)-2-pyrrolidinecarboxamide ("Hua Cat") and N-(carboxy-p-dodecylphenylsulfonyl)-2-pyrrolidinecarboxamide ("Hua Cat-II") by Yang and Carter. Specific reactions covered include the aldol reaction, Mannich reaction, formal aza-Diels-Alder reaction, tandem Michael/Mannich reaction and Yamada-Otani reaction. The ability of proline aryl sulfonamides to construct all-carbon quaternary stereocenters in high enantioselectivity and diastereoselectivity is a notable feature of the reported work. The practicality of this chemistry for large scale and industrial applications is also included. Finally, a discussion of the future directions of proline sulfonamide organocatalysis is provided.

Asymmetric syntheses of (-)-enterolactone and (7'R)-7'-hydroxyenterolactone via organocatalyzed aldol reaction

Short syntheses of (-)-enterolactone (1a) and (7'R)-7'-hydroxyenterolactone (1b) have been achieved utilizing organocatalyzed asymmetric cross-aldol reaction of aldehydes 2 and 3 and base-mediated alkylation of lactones 5 and 4.