CuBr2-catalyzed diastereoselective allylation: total synthesis of decytospolides A and B and their C6-epimers

An efficient CuBr₂-catalyzed diastereoselective allylation of a cyclic hemiacetal with allyltrimethylsilane as a nucleophile has been developed. The protocol offers a cost effective, protecting group tolerant, and operationally simple approach to 2,6-trans-disubstituted tetrahydropyran with excellent diastereoselectivity. Furthermore, the application of this methodology has been demonstrated in the total synthesis of decytospolides A and B and their C6-epimers.

The Mukaiyama type aldol reaction for the synthesis of trans-2,6-disubstituted tetrahydropyrans: synthesis of diospongin A and B

An efficient synthesis protocol for the preparation of trans-2,6-disubstituted tetrahydropyrans by the reaction of 1-phenyl-1-triemthylsiloxyethylene with six membered cyclic hemiacetals in the presence of iodine is developed. This reaction proceeds smoothly under mild conditions employing a catalytic amount of molecular iodine. The feature of this novel conversion includes milder reaction conditions, broader substrate scope, functional group tolerance and good diastereoselectivity. The efficiency and practicality of the current method were successfully displayed in the total synthesis of diospongin A and B in good yields.

A General Diastereoselective Strategy for Both cis- and trans-2,6-Disubstituted Tetrahydropyrans: Formal Total Synthesis of (+)-Muconin

A protocol for general diastereoselective tandem dihydroxylation followed by S_N2 cyclization was developed for the convenient and efficient synthesis of cis- and trans-2,6-disubstituted tetrahydropyrans from ζ-mesyloxy α,β-unsaturated esters. The application of this novel method was demonstrated through the concise formal synthesis of (+)-muconin, a nonclassical acetogenin, with sequential THP-THF ring formation.

Can a Ketone Be More Reactive than an Aldehyde? Catalytic Asymmetric Synthesis of Substituted Tetrahydrofurans

O-heterocycles bearing tetrasubstituted stereogenic centers are prepared via catalytic chemo- and enantioselective nucleophilic additions to ketoaldehydes, in which the ketone reacts preferentially over the aldehyde. Five- and six-membered rings with both aromatic and aliphatic substituents, as well as an alkynyl substituent, are obtained. Moreover, 2,2,5-trisubstituted and 2,2,5,5-tetrasubstituted tetrahydrofurans are synthesized with excellent stereoselectivities. Additionally, the synthetic utility of the described method is demonstrated with a three-step synthesis of the side chain of anhydroharringtonine.

Transition-Metal-Free Cross-Coupling of Indium Organometallics with Chromene and Isochroman Acetals Mediated by BF3·OEt2

A transition-metal-free coupling of triorganoindium reagents with benzopyranyl acetals mediated by a Lewis acid has been developed. The reaction of R3In with chromene and isochroman acetals in the presence of BF3·OEt2 afforded 2-substituted chromenes and 1-substituted isochromans, respectively, in good yields. The reactions proceed with a variety of triorganoindium reagents (aryl, heteroaryl, alkynyl, alkenyl, alkyl) using only 50 mol % of the organometallic, thus demonstrating the efficiency of these species. Preliminary mechanistic studies indicate the formation of an oxocarbenium ion intermediate in the presence of the Lewis acid.

Gold-catalyzed diastereoselective synthesis of 2,6-trans-disubstituted tetrahydropyran derivatives: application for the synthesis of the C1–C13 fragment of bistramide A and B

An efficient Au(iii)-catalyzed diastereoselective allylation leading to 2,6-trans-disubstituted tetrahydropyrans and application for the synthesis of the C1–C13 fragment of bistramide A and B is described.