A rhodium(III)‐catalyzed selective olefination of picolinamide derivatives has been developed. The reaction shows high regioselectivity, low catalyst loading (0.5 mol%), high yield and good functional group tolerance, providing a convenient strategy for the synthesis of 3‐alkenylpicolinamides.
1,1,1‐Trifluoroacetone tosylhydrazone is presented as a very convenient substrate for the palladium‐catalyzed cross‐coupling with aryl halides. Under the proper reaction conditions, 3,3,3‐trifluoromethylstyrenes – very valuable trifluoromethylated synthetic intermediates – are obtained with high yields. The reaction features a very wide scope, as the presence of most functional groups is tolerated. Moreover, the reaction has been extended to substituted trifluoromethylstyrenes by employing substituted tosylhydrazones derived from other trifluoromethyl ketones.
A simple and efficient protocol was developed for the synthesis of 2‐iminothiazolidines through a base‐mediated [3+2] annulation involving substituted thioureas and allylic bromides bearing electron‐withdrawing groups. This domino process consists of nucleophilic displacement, followed by intramolecular anti‐Michael addition of the preformed allylic isothiourea under mild conditions to give the thiazolidine core.
An efficient regioselective synthesis of 2‐acylpyrroles via palladium‐catalyzed addition of pyrroles with benzonitriles and subsequent hydrolysis is developed. The direct acylation reaction of protected as well as (NH)‐free pyrroles proceeded smoothly to afford 2‐acylpyrrole scaffolds of high biological interest.
Readily available cyclobutanols having a butyne‐1,4‐diol moiety underwent a sequential regioselective Meyer–Schuster rearrangement and 1,2‐shift, furnishing α‐hydroxy‐α‐vinylcyclopentanones. The reaction mechanism is consistent with the formation of an allenol intermediate that racemizes under the reaction conditions. Subsequent activation of the allenol leads to an enantio‐ and diastereoselective route to this scaffold.
A copper‐catalyzed cascade reaction involving trifluoromethylation of acrylamides coupled with ring closure and indole dearomatization is reported. This facile transformation was highly regioselective and proceeded under mild conditions, allowing efficient access to trifluoromethyl‐substituted spiro[indole‐3,3′‐pyrrolidine] derivatives, which are of increasing interest to the pharmaceutical industry.
An efficient strategy for the regioselective ortho‐acylation of azoxybenzenes with various aldehydes in the presence of palladium catalysts has been developed and furnishes good to excellent yields. The reaction proceeds smoothly and can tolerate a variety of functional groups.
An efficient method for the construction of cyclopropane‐fused dihydroquinolines was established by a novel Povarov‐type three‐component reaction of aromatic aldehydes, anilines and cyclopropenes in the presence of trifluoromethanesulfonic acid. The reaction proceeded in a regioselective and diastereoselective manner. Furthermore, the dihydroquinolines were smoothly converted to benzazepine derivatives via a ring opening/isomerization sequence, further expanding the synthetic scope.
Multifunctional 3‐amino‐4‐dialkylphosphono‐2‐quinolinones have been prepared by “one‐pot” nucleophilic addition and regioselective ring enlargement of imino isatins. The addition reaction between imino isatins and dialkyl (diazomethyl)phosphonate proceeds smoothly using potassium carbonate as a catalyst, and a subsequent regioselective ring expansion promotes by salicylic acid to afford the desired products in high yields.
A direct enantioselective reaction of cyclopent‐2‐enone‐derived Morita–Baylis–Hillman alcohols with 4‐hydroxycoumarins has been developed under the catalysis of a chiral primary amine derived from cinchonine in combination with a Brønsted acid. The reaction provides pyranocoumarin products with three vicinal chiral carbon centers in highly regio‐, diastereo‐ and enantioselectivities through a tandem allylic alkylation/intramolecular oxa‐Michael addition.
A series of 1,2‐ and 1,4‐dihydroquinolines has been successfully prepared. The Pd‐catalyzed intramolecular N‐arylation of Z‐enamines, formally prepared by the Horner–Wadsworth–Emmons olefination, proceeded efficiently to furnish the cyclized products. Depending on the cyclization conditions, substituted 1,4‐dihydroquinolines and further isomerized 1,2‐dihydroquinolines were independently obtained in high yields with an excellent control of isomerization of the double bond.
An efficient approach for the synthesis of 1,2,3,4,5,6‐hexahydrobenzo[f]isoquinolines via a tandem aza‐Prins/Friedel–Crafts cyclization from 2‐arylethyl‐2,3‐butadienyl tosylamides and aldehydes has been developed. This iron(III) chloride‐catalyzed cascade cyclization at the room temperature with different types of aldehydes, such as aromatic and heteroaromatic aldehydes, alkyl aldehydes, and α,β‐unsaturated aldehydes, affords the products in moderate to excellent yields (up to 97 %). In this reaction, chlorotrimethylsilane was applied to activate the aldehydes. The cheap catalyst, the mild reaction conditions, and the broad scope of the substrates make this method highly useful.
A novel and efficient domino process has been developed for the synthesis of 1,4‐benzoxazepine derivatives from a range of readily accessible N‐tosylaziridines, 2‐iodophenols and isocyanides. This process involves the aziridine ring‐opening reaction with 2‐iodophenol, followed by a palladium‐catalyzed isocyanide‐insertion reaction. This regioselective and high‐yielding transformation could be extended to its application for the synthesis of natural products and biologically interesting heterocycles.
A novel regioselective α‐arylation of coumarins with readily available arenesulfonyl chlorides and sodium arenesulfinates via palladium‐catalyzed direct C H functionalizations under mild reaction conditions is described. This protocol presents an unexpected and highly regio‐controlled arylation of coumarins at C‐3 to construct interesting 3‐arylcoumarins with fascinating biological and fluorescent properties. The regioselectivity observed is in sharp contrast with that expected for the Heck reactions.
A cationic gold(I)‐catalyzed decarboxylative etherification of propargyl carbonates to selectively produce propargyl ethers is reported. In the reaction the gold(I) catalyst shows a distinct σ‐Lewis acidity rather than the commonly observed π‐Lewis acidity, and thus catalyzes the decarboxylation of a variety of propargyl carbonates to give the corresponding propargyl ethers with high selectivity. This reaction represents a rare example of the tunable reactivity of cationic gold(I) complexes between σ‐Lewis acidity and π‐Lewis acidity.
The 8‐aminoquinoline‐directed, nickel(II)‐mediated ortho‐iodination of benzamides using molecular iodine has been developed. The process is highly regioselective and furnishes only monoiodinated products. A broad range of arenes and heteroarenes with diverse functional groups provided monoiodinated products in good to excellent yields.
A new silver(I) triflate‐promoted tandem reaction comprising the ring opening of aziridines and a Michael reaction has been developed. Using secondary amines or primary amines as nucleophiles, this methodology allows for the synthesis of cis‐1‐alkyl‐4‐aminotetrahydroisoquinolines or cis‐1,3‐disubstituted isoindolines in good yields with excellent diastereoselectivities, respectively. Besides, easy operation and mild reaction conditions are also notable features of this tandem reaction.
A new and efficient nickel‐based protocol for the N‐arylation of indoles and carbazoles with aromatic chlorides, the least expensive of the aryl halides, is described. The procedure provides selectively N‐(hetero)arylation products in good to high yields, in short reaction times and without adding an excess of ligands.
The reaction of glyceraldehyde with alkynes delivers furfuryl alcohol derivatives within only one reaction step in the presence of a gold(III) catalyst. The reaction cascade is initiated by an intermolecular gold‐catalyzed A3 coupling sequence in which morpholine is used as additive. Intramolecular cyclization and subsequent aromatization under elimination of the amine then deliver the target molecules. The protocol offers a valuable alternative to the common routes that are based on functionalization of already existing furan cores.
A method for using amine–borane complexes directly in palladium catalyzed borylation has been developed. The reaction proceeds through the sequential formation of a boronium species followed by deprotonation leading to the aminoborane. This reagent is then directly used in the borylation process leading, after work‐up, to various boronic acid derivatives. The reaction was applied to (hetero)aryl triflates, iodides, bromides and chlorides.
