Palladium‐Catalyzed [4+2] Cycloaddition of Hydroxy‐Tethered Allylic Carbonates with Alkenes: Synthesis of Functionalized Tetrahydropyrans

Abstract

A palladium‐catalyzed [4+2] cycloaddition of hydroxy‐tethered allyl carbonates with five types of electron‐deficient alkenes has been achieved, in which a type of new hydroxy‐tethered allyl carbonates acted as valuable precursors for the formation of 1,4‐C,O‐dipole allylpalladium intermediates. The reaction proceeded efficiently under mild reaction conditions to provide the corresponding tetrahydropyran derivatives in moderate to high yields with excellent diastereoselectivities.

Palladium-catalyzed asymmetric (4 + 3) cycloaddition of N-2,2,2-trifluoroethylisatin ketimines: access to optically active spirooxindoles

“…Based on our experimental results and the reported literature, 10,11 a possible reaction pathway was proposed. As shown in Scheme 4, initially, the oxygen anion of the π-allylpalladium intermediate E was formed by decarboxylation of substrate 2 , which first acted as a Brønsted base to abstract the proton of substrate 1 , affording intermediate A .…”

Pd-catalyzed oxa-[4 + n] dipolar cycloaddition using 1,4-O/C dipole synthons for the synthesis of O-heterocycles

“…Furthermore, in 2022, the same group reported diastereoselective oxa-[4 + 2] dipolar cycloadditions of 2-aryl- or 2-alkyl-substituted 2-hydroxymethylallyl carbonates 2 with five different types of trisubstituted alkenes 13–15 , 19 and 20 , which afforded spirocyclic compounds 16′–18′ and multisubstituted tetrahydropyrans 21 and 22 (Scheme 6B). 16 The [4 + 2] cycloadducts were obtained in high yields with excellent dr values (>20 : 1 dr in all cases) using Pd 2 (dba) 3 ·CHCl 3 and L7 or PPh 3 as a ligand. A plausible reaction mechanism to explain the diastereoselectivity of the reaction of 2 and indandiones 14 was proposed.…”

Palladium-catalyzed [4 + 2] cycloaddition of amido-tethered allylic carbonates with oxazol-5-(4H)-ones: synthesis of piperidine-2,6-dione derivatives

“…The π-allyl-Pd oxa-1,4-dipoles were synthesized to realize a number of useful [4 + 2] cycloaddition reactions with various alkenes. 12 c ,13–17 The [6 + 5], [5 + 4] and [4 + 5] cycloaddition reactions of isatin derivatives through π-allyl-Pd oxa-1,6/5/4-dipoles were also developed for modular synthesis of medium-sized fluorinated and nonfluorinated heterocyclic lactones. 18 In addition to these types of oxygen-containing π-allylpalladium zwitterionic intermediates, aza-1,4-dipoles have also been prepared by decarboxylation from vinyl oxazinanones or benzovinyloxazinones to synthesize nitrogen-containing heterocycles (Scheme 1c).…”