Search

A variety of tetrahydro-5 H -indolo[2,3- b ]quinolines were prepared in 40-97% yields through a copper(II)-catalyzed cascade reaction of aza- o -quinone methides generated in situ from 2-(chloromethyl)anilines and indoles. Experimental results showed that the reaction underwent double 1,4-additions and sequential intramolecular cyclization. The present method features broad substrate scope, good functional group tolerance, and easy gram scalable preparation of indolo[2,3- b ]quinolines.

An approach for the construction of furo[3,2- b ]quinolines and furo[2,3- b :4,5- b' ]diquinolines is developed through a metal-free [4 + 2] cycloaddition of easily available in situ generated aza- o -quinone methides and furans. The reaction tolerates a wide range of aza- o -quinone methides and substituted furans to afford the corresponding dihydro- or tetrahydrofuroquinolines in good to excellent yields. Mechanistic studies reveal that the reaction involves a concerted [4 + 2] cycloaddition pathway and shows a high regioselectivity of cycloaddition for a furan ring. The present method features mild reaction conditions, dearomatization of furans, high regio- and diastereoselectivity, gram-scalable preparations, and diversity of furoquinolines.

An atom-economical and practical method for the efficient synthesis of various pyrazino[1,2- a ]indole-2-oxides was developed through a nickel(II)-catalyzed [5 + 1] annulation of 2-carbonyl-1-propargylindoles with hydroxylamine in water without using an organic solvent. The reaction involved an initial condensation of 2-carbonyl-1-propargylindoles with hydroxylamine to afford oxime intermediates, which then underwent a nickel(II)-catalyzed 6-exo-dig cyclization. Preliminary studies showed that ( n -Bu) 4 NI served as a phase transfer catalyst and promoted the formation of active nickel(II) species. More importantly, the nickel(II) salt and phase transfer catalyst-in-water could be recycled seven times, and a gram scalable product was easily obtained in good yields through a filtration and washing protocol.

A series of 1,2- and 2,3-fused quinazolinones have been synthesized in good to excellent yields through gold-catalyzed selective hydroarylations of alkynyl quinazolinone-tethered pyrroles. The studies revealed that 1,2-fused quinazolinones were obtained through a 1,3-rearrangement and sequential 6- exo-trig cyclization of N1-alkynyl quinazolinone-tethered pyrroles, while N3-alkynyl quinazolinone-tethered pyrroles went through 6- exo-dig or 7- endo-dig cyclizations directly to afford 2,3-fused quinazolinones. The fused quinazolinones could be prepared at gram scale in three steps from commercial ortho-aminobenzamide.

An efficient method to synthesize rutaecarpine derivatives via the gold-catalyzed selective cyclization of alkyn-tethered indoles under mild conditions is described. The alkyn-tethered indole can undergo 6-exo-dig cyclization by oxidation and sequential gold catalysis, while it goes through 7-endo-dig cyclization by gold catalysis and sequential oxidation. Substrate scope studies reveal that the selectivity of cyclization was controlled by the substrates with sp 3 and sp 2 hybridization of carbon at the 2 position in quinazolinone. Furthermore, the rutaecarpine scaffold was prepared in 67% yield at gram scale easily in four steps from isatoic anhydride.

A copper-catalyzed selective cross-coupling reaction of 3-(hydroxyimino)indolin-2-ones with alkenyl boronic acids to access (E)-N-vinyl oxindole nitrones has been achieved under mild conditions. The studies showed that catalytic copper salt selectively gave mono N-vinylation products, while 2.0 equiv of copper salt provided double N-vinylation products. The control experiments revealed that the carbonyl group in 3-(hydroxyimino)indolin-2-one played important roles on N-vinylation. Furthermore, the prepared N-vinyl oxindole nitrones could be converted to spirooxindoles in good yields under thermal conditions.

An efficient selective N-arylation of 3-(hydroxyimino)indolin-2-ones with diaryliodonium salts to prepare (Z)-N-aryl oxindole nitrones has been achieved under simple base-mediated conditions. The reaction tolerated a variety of diaryliodonium salts with diverse and sensitive functional groups. Studies on the oxime structures revealed that the pyrroline ring and carbonyl group in 3-(hydroxyimino)indolin-2-ones played important roles in the selective N-arylation process. The N-aryl oxindole nitrones could be prepared rapidly and easily at the gram scale.

A facile synthesis of various spirofluorenylpiperidin-4-ones has been achieved in good yields from fluorenone N-aryl nitrones and methylenecyclopropanes. This method involved an initial cycloaddition to form a 5-spirocyclopropane-isoxazoline, which underwent a highly selective 1,3-rearrangement to give the desired product. The stereochemistry of the spirofluorenylpiperidin-4-one could be controlled by the cycloaddition and sequential rearrangement strategy. Furthermore, the spirofluorenylpiperidin-4-ones could be not only prepared in one-pot procedure but also converted to useful scaffolds by reduction or oxidation conditions.

A metal-free method for synthesis of N-(2-hydroxyaryl)benzotriazoles via O-arylation of N-hydroxybenzotriazoles with readily available diaryliodonium salts and sequential N-O bond cleavage under mild conditions has been developed. The [3,3]-rearrangement of N-O bond cleavage could take place on the N instead of C atom. The reaction was compatible with diverse functional groups and a new type of P,N-ligand was synthesized in three steps.

Metal-free O-arylation and [3, 3]-rearrangement have been shown as an efficient strategy to construct new C-O and C-N bonds in one-pot reactions. The method was used to prepare N-aryl benzo[1,2,3]triazin-4(1H)-one derivatives in good yields from N-hydroxy benzo[1,2,3]triazin-4(3H)-one and diaryliodonium salts. The reaction was tolerated a variety of sensitive functional groups such as iodine, nitro, ester, and aldehyde groups. A rational mechanism was proposed based on the experimental results, and the reaction was easily up to gram scale.

An efficient transition-metal-free method for the preparation of α,β-unsaturated N-aryl ketonitrones under mild conditions has been developed. This reaction shows good functional group tolerance for both electron-rich and electron-deficient substituents on both oximes and diaryliodonium salts. Two examples of gram-scale preparations have been realized in good yields. Further transformations of these nitrones to different N-heterocycles have been demonstrated. DFT calculations suggest that N-arylation products are formed by [1,3]-phenyl migration of an O-coordinated oximate complex via a four-centered transition state, while the O-arylation products are formed by [1,3]-phenyl migration of a N-coordinated oximate complex.

Efficient access to α,α'-diacetoxy ketones has been developed from ethynylcarbinols and PhI(OAc)2. A plausible mechanism for this was proposed on the basis of experimental studies. The usefulness of α,α'-diacetoxy ketone products has been documented, and glycerol derivatives can be easily synthesized in good yields via a one-pot reaction.

An efficient way to access functionalized methylenecyclopropanes has been developed by palladacycle-catalyzed cyclopropanation of bicyclic alkenes with propiolates in high yields. The structure of the palladacycle was kept intact in the reaction, shown by (31)P NMR spectrum studies. A rational mechanism has been proposed with a deuterium-labeled experiment. The usefulness of the functionalized methylenecyclopropanes has also been demonstrated.