Six-membered ring systems: with O and/or S atoms

A large variety of publications involving O- and S-6-membered ring systems have appeared in 2017. The importance of these heterocyclic compounds is highlighted by the huge number of publications on the total synthesis of natural oxygen derivatives and of other communications dedicated to synthetic derivatives. Reviews on stereoselective organocatalytic synthesis of tetrahydropyrans (17EJO4666), of tetrahydropyrans and their application in total synthesis of natural products (17CSR1661), on the synthesis of the less thermodynamically stable 2,6-trans-tetrahydropyrans (17S4899), on enantioselective synthesis of polyfunctionalized pyran and chromene derivatives (17TA1462), and on enantioselective and racemic total synthesis of camptothecins, including the formation of their pyran-2-one ring (17SL1134), have appeared. Advances in the transition metal-catalyzed synthesis of pyran-2/4-ones (17TL263), N-heterocyclic carbene (NHC)-catalyzed achiral synthesis of pyran-2-one, coumarin and (thio)chromone derivatives (17OBC4731), on the synthesis and transformation of 2H-pyran-2-ones (17T2529) and 2-styrylchromones (17EJO3115) into other heterocyclic compounds, have been surveyed. The strategies to build up the tetrahydropyranyl core of brevisamide (17H(95)81) and the reactions of ketyl radicals, generated from carbonyl derivatives under transition-metal photoredox-catalyzed conditions, leading to isochromen- and chroman-type compounds (17CC13093) were disclosed. Developments in the synthesis of pentafluorosulfanyl(chromene and coumarin) derivatives (17TL4803), photoswitchable D9-tetrahydrocannabinol derivatives (17JA18206), and aminobenzopyranoxanthenes with nitrogen-containing rings (17JOC13626) have been studied.info:eu-repo/semantics/publishedVersio

Catalytic asymmetric formal gamma-allylation of deconjugated butenolides

A formal gamma-allylation of deconjugated butenolides is reported based on a two-step sequence consisting of a catalytic diastereo- and enantioselective vinylogous nucleophilic addition to vinyl sulfones and Julia-Kocienski olefination. This highly modular approach delivers densely functionalized butenolides containing a quaternary stereogenic centre in excellent yield with high enantioselectivity

Catalytic Enantioselective Synthesis of 3,4-Unsubstituted Thiochromenes through Sulfa-Michael/Julia–Kocienski Olefination Cascade Reaction

A highly enantioselective cascade sulfa-Michael/Julia–Kocienski olefination reaction between 2-mercaptobenzaldehydes and β-substituted vinyl PT-sulfones has been realized for the synthesis of 3,4-unsubstituted 2<i>H</i>-thiochromenes. This reaction, catalyzed by diphenylprolinol TMS ether, proceeds through an aromatic iminium intermediate and furnishes a wide range of 2-substiuted 2<i>H</i>-thiochromenes with excellent enantioselectivities (up to 99:1 er)

A Catalytic Enantioselective lodocyclization Route to Dihydrooxazines

The first catalytic enantioselective synthesis of 5,6-dihydro-4H-1,2-oxazines bearing an oxygen-containing quaternary stereogenic center has been developed through iodoetherification of gamma,delta-unsaturated oximes. This operationally straightforward reaction is catalyzed by Cinchona alkaloids-based bifunctional tertiary aminothiourea derivatives and furnishes the products generally in good to excellent yields and with moderate to high enantioselectivities (up to 97:3 er)

Enantioselective Hydroalkenylation and Hydroalkynylation of Alkenes Enabled by a Transient Directing Group

The catalytic enantioselective synthesis of α-chiral alkenes and alkynes represents a powerful strategy for rapid generation of molecular complexity. Herein, we report a transient directing group facilitated site-selective palladium-catalyzed reductive Heck-type hydroalkenylation and hydroalkynylation of alkenylaldehyes using alkenyl and alkynyl bromides, respectively, allowing for construction of a stereocenters at the δ position with respect to the aldehyde

A Catalytic Enantioselective Iodocyclization Route to Dihydrooxazines

The first catalytic enantioselective synthesis of 5,6-dihydro-4<i>H</i>-1,2-oxazines bearing an oxygen-containing quaternary stereogenic center has been developed through iodoetherification of γ,δ-unsaturated oximes. This operationally straightforward reaction is catalyzed by <i>Cinchona</i> alkaloids-based bifunctional tertiary aminothiourea derivatives and furnishes the products generally in good to excellent yields and with moderate to high enantioselectivities (up to 97:3 er)

Catalytic Addition of Nitroalkanes to Unactivated Alkenes via Directed Carbopalladation

We report a redox-neutral catalytic coupling of nitroalkanes and unactivated alkenes that proceeds by a directed carbopalladation mechanism. The reaction is uniquely enabled by the combination of PdI2 as the precatalyst and HFIP solvent. Structurally complex nitroalkane products, including nitro-containing carbo- and heterocycles, are prepared under operationally convenient conditions without the need for toxic or corrosive reagents. Deuterium labeling experiments and isolation of a catalytically relevant intermediate shed light on the reaction mechanism. By taking advantage of different catalytic activation modes, we demonstrate orthogonal methods for site-selective functionalization of a polyfunctional nitroalkyl ketone

A Catalytic Enantioselective Iodocyclization Route to Dihydrooxazines

The first catalytic enantioselective synthesis of 5,6-dihydro-4<i>H</i>-1,2-oxazines bearing an oxygen-containing quaternary stereogenic center has been developed through iodoetherification of γ,δ-unsaturated oximes. This operationally straightforward reaction is catalyzed by <i>Cinchona</i> alkaloids-based bifunctional tertiary aminothiourea derivatives and furnishes the products generally in good to excellent yields and with moderate to high enantioselectivities (up to 97:3 er)