Recent Advances in Palladium-Catalyzed [4 + n] Cycloaddition of Lactones, Benzoxazinanones, Allylic Carbonates, and Vinyloxetanes

Palladium-catalyzed allylation cyclization reaction has recently emerged as an efficient and powerful synthetic platform for the construction of diverse and valuable carbo- and heterocycles. Thus the development of new allylic motifs for achieving this type of transformations in high reactivity and selectivity is of great importance. Generally, these substrates have been utilized as 1,3-, 1,4-, 1,5-, 1,6-dipoles in many reactions, which are applied to prepare highly functionalized products with complete control of chemo-, regio-, diastereo-, and enantioselectivity. In this review, we focus our attention on the development of palladium-catalyzed [4 + n] cycloaddition of allylic motifs and describe a comprehensive and impressive advances in this area. Meanwhile, the related mechanism and the application of these annulation strategies in natural product total synthesis will be highlighted in detail.

Silver/chiral pyrrolidinopyridine relay catalytic cycloisomerization/(2 + 3) cycloadditions of enynamides to asymmetrically synthesize bispirocyclopentenes as PDE1B inhibitors

Significant progress has been made in asymmetric synthesis through the use of transition metal catalysts combined with Lewis bases. However, the use of a dual catalytic system involving 4-aminopyridine and transition metal has received little attention. Here we show a metal/Lewis base relay catalytic system featuring silver acetate and a modified chiral pyrrolidinopyridine (PPY). It was successfully applied in the cycloisomerization/(2 + 3) cycloaddition reaction of enynamides. Bispirocyclopentene pyrazolone products could be efficiently synthesized in a stereoselective and economical manner (up to >19:1 dr, 99.5:0.5 er). Transformations of the product could access stereodivergent diastereoisomers and densely functionalized polycyclic derivatives. Mechanistic studies illustrated the relay catalytic model and the origin of the uncommon chemoselectivity. In subsequent bioassays, the products containing a privileged drug-like scaffold exhibited isoform-selective phosphodiesterase 1 (PDE1) inhibitory activity in vitro. The optimal lead compound displayed a good therapeutic effect for ameliorating pulmonary fibrosis via inhibiting PDE1 in vivo.

Organocatalytic (5+1) benzannulation of Morita–Baylis–Hillman carbonates: synthesis of multisubstituted 4-benzylidene pyrazolones

DABCO-catalyzed (5+1) cycloaddition of MBH carbonate undergoes an α-double deprotonation pathway to de novo assemble the benzene ring.

Asymmetric Decarboxylative [3+2] Cycloaddition for the Diastereo- and Enantioselective Synthesis of Spiro[2.4]heptanes via Cyclopropanation

Asymmetric cycloaddition reaction has emerged as one of the powful and reliable strategies for the construction of enantioenriched molecules, especially those with polycyclic frameworks. Herein, we report the asymmetric decarboxylative...

Diastereodivergent synthesis of fully disubstituted spiro[indoline-3,2′-pyrrolidin]-2-ones via tuneable Lewis base/Brønsted base-promoted (3 + 2) cycloadditions

We have developed unique base-promoted diastereoselective (3 + 2) cycloadditions. A diastereodivergent synthesis of fully disubstituted spiro[indoline-3,2′-pyrrolidin]-2-ones was realized by tuning a Lewis base/Brønsted base.

Cooperative Palladium-Catalyzed and P(NEt2)3-Mediated (4+1) Annulation of Isatins with 2-Hydroxymethylallylcarbonates

P(NR2)3-promoted transformations of isatins with electron-withdrawing alkenes have received consistently attention over the last decades. However, no example involving chemical transformations of nonactivated or weakly activated alkenes is discovered in...