Chelation-assisted iridium-catalyzed hydroalkenylation and hydroarylation/cyclization with conjugated trienes.

Iridium-catalyzed hydroalkenylation of conjugated trienes by chelation-assisted alkenyl C-H activation of acrylamides has been demonstrated to produce 1,4,6-trienes atom efficiently with excellent - and / selectivities. In contrast, the reaction of benzamides and 1,3,5-trienes proceeds by a tandem hydroarylation of the trienes and cyclization intramolecular 1,2-addition, providing valuable -tetrahydroisoquinolinone derivatives. A broad range of aromatic and aliphatic 1,3,5-trienes bearing various functionalities were compatible to deliver target products with high yields and / selectivity.

Functionality-Directed Regio- and Enantio-Selective Olefinic C-H Functionalization of Aryl Alkenes.

Aryl alkenes represents one of the most widely occurring structural motif in countless drugs and natural products, and direct C-H functionalization of aryl alkenes provides atom- step efficient access toward valuable analogues. Among them, group-directed selective olefinic α- and β-C-H functionalization, bearing a directing group on the aromatic ring, has attracted remarkable attentions, including alkynylation, alkenylation, amino-carbonylation, cyanation, domino cyclization and so on. These transformations proceed by endo- and exo-C-H cyclometallation and provide aryl alkene derivatives in excellent site- stereo-selectivity.

Synthesis of 3-Oxo Quinolines by Cyclization Using Lignin Models and 2-Aminobenzyl Alcohols.

Phenoxy acetophenones were usually employed as β-O-4' lignin models for chemical conversion. Herein, an iridium-catalyzed dehydrogenative annulation between 2-aminobenzylalcohols and phenoxy acetophenones was demonstrated to prepare valuable 3-oxo quinoline derivatives, which are hard to prepare using previous methods. This operationally simple reaction tolerated a wide scope of substrates and enabled successful gram-scale preparation.

Recent advances in chelation-assisted site- and stereoselective alkenyl C-H functionalization.

Olefinic C-H functionalization represents an atom- and step economic approach to valuable olefin derivatives from simpler ones, but controlling the selectivity remains a challenge. Remarkable progress has been made in the site-selective C-H functionalization of arenes and alkanes, but there are still limited examples of selective C-H functionalization of olefins presumably due to the lability and easy decomposition of the alkenyl moiety. Chelation-assisted C-H activation represents an efficient protocol for site- and stereo-selective construction of carbon-carbon and carbon-heteroatom bonds.

Ruthenium-Catalyzed Brook Rearrangement Involved Domino Sequence Enabled by Acylsilane-Aldehyde Corporation.

A ruthenium-catalyzed [1,2]-Brook rearrangement involved domino sequence is presented to prepare highly functionalized silyloxy indenes with atomic- and step-economy. This domino reaction is triggered by acylsilane-directed C-H activation, and the aldehyde controlled the subsequent enol cyclization/Brook Rearrangement other than β-H elimination. The protocol tolerates a broad substitution pattern, and the further synthetic elaboration of silyloxy indenes allows access to a diverse range of interesting indene and indanone derivatives.

Stereoselective and Atom-Economic Alkenyl C-H Allylation/Alkenylation in Aqueous Media by Iridium Catalysis.

A practical and atom-economic protocol for the stereoselective preparation of various 1,4- and 1,3-diene skeletons through iridium-catalyzed directed olefinic C-H allylation and alkenylation of NH-Ts acrylamides in water was developed. This reaction tolerated a wide scope of substrates under simple reaction conditions and enabled successful gram-scale preparation. Furthermore, an asymmetric variant of this reaction giving enantioenriched 1,4-dienes was achieved employing a chiral diene-iridium complex as the catalyst.

Bidentate auxiliary-directed alkenyl C-H allylation via exo-palladacycles: synthesis of branched 1,4-dienes.

An alkenyl C-H allylation by an exo-palladacycle intermediate is demonstrated, employing unactivated (Z)-alkenes and allyl carbonates. With the use of an 8-aminoquinoline (AQ) derived amide as the directing group, the N,N-bidentate-chelation-assisted C-H activation protocol proceeded under mild and oxidant-free conditions with excellent selectivity. The utility of this approach is demonstrated by the preparative scale, selective conversion of inseparable Z/E alkenes and ready removal of the amide auxiliary to provide the corresponding ester.

Iridium-Catalyzed Cross-Coupling Reactions of Alkenes by Hydrogen Transfer.

A range of Ru-, Rh-, or Pd-catalyzed vinylic C-H/C-H cross-coupling reactions of olefins have been demonstrated to provide 1,3-dienes, using a quantitative amount of metal oxidants. Although transfer hydrogenation and C-H alkenylation are two important areas that evolved independently, we herein report the first iridium-catalyzed cross-coupling reactions of alkenes by integration of directed C(alkenyl)-H alkenylation and transfer hydrogenation to obviate the usage of a metal oxidant, employing a hydrogen acceptor such as inexpensive chloranil.

NHC-catalyzed [4+2] cycloaddition reactions for the synthesis of 3'-spirocyclic oxindoles via a C-F bond cleavage protocol.

A chiral NHC-catalyzed cycloaddition of γ-fluoroenals is developed. The nucleophilic γ-carbon generated via C-F bond cleavage undergoes highly enantioselective cycloaddition (up to >99% ee) to isatins and provides 3'-spirocyclic oxindoles in good yields (up to 91%).

Facile Preparation of (2Z,4E)-Dienamides by the Olefination of Electron-deficient Alkenes with Allyl Acetate.

Direct cross-coupling between two alkenes via vinylic C-H bond activation represents an efficient strategy for the synthesis of butadienes with high atomic and step economy. However, this functionality-directed cross-coupling reaction has not been developed, as there are still limited directing groups in practical use. In particular, a stoichiometric amount of oxidant is usually required, producing a large amount of waste.

N-Heterocyclic Carbene-Catalyzed Activation of Esters of N-Hydroxyphthalimide: A Highly Enantioselective Route to Chiral Dihydropyridinones Bearing an All Carbon Quaternary Stereogenic Center.

An N-heterocyclic carbene-catalyzed highly enantioselective [3 + 3] annulation reaction of N-hydroxyphthalimide (NHPI) 3,3-disubstituted acrylates and N-Ts ketimines was developed. In most cases, the desired chiral dihydropyridinone products bearing an all carbon quaternary stereogenic center could be obtained in good yields with excellent enantioselectivities (>99% ee's), which demonstrated the NHPI acrylates as a kind of excellent substrate in NHC-catalysis.

Triflic acid catalyzed formal [3 + 2] cycloaddition of donor-acceptor oxiranes and nitriles: a facile access to 3-oxazolines.

A TfOH-catalyzed chemoselective [3 + 2] cycloaddition of donor-acceptor oxiranes and nitriles is described. This reaction provides an efficient and practical method for the preparation of useful 3-oxazolines in good to excellent yields (up to 99%).