[Cu( malo NHC)]-catalyzed synthesis of 2-aryl pyrazolo[5,1- a ]isoquinolines by annulation of N ′-(2-((trimethylsilyl)ethynyl)benzylidene)hydrazides with terminal aromatic alkynes

[3 + 2] Cycloaddition of N-Amino(iso)quinolinium Salts with Vinylsulfonium Salt: Synthesis of Pyrazolo[1,5-a]quinoline and Pyrazolo[5,1-a]isoquinoline Derivatives

In this study, we reported the utilization of vinylsulfonium salt as a highly efficient dipolarophile, leveraging the facile leaving ability of its sulfide moiety, to engage in a [3 + 2] cycloaddition with N-amino(iso)quinolinium salts. This approach facilitates the construction of various C1/C2-unsubstituted pyrazolo(iso)quinoline skeletons. The transformation is conducted under catalyst- and external oxidant-free conditions. Furthermore, the extended gram-scale reaction demonstrates the practical applicability of the developed protocol.

LiOtBu-Promoted Intramolecular 1,3-Dipolar Cycloaddition of the 2'-Alkynyl-biaryl-2-aldehyde N-Tosylhydrazones Approach to 3-Substituted 1H-Dibenzo[e,g]indazoles

A two-step, one-pot synthesis of 3-substituted 1H-dibenzo[e,g]indazoles in good to high yields via a LiOtBu-promoted intramolecular 1,3-dipolar cyclization of 2'-alkynyl-biaryl-2-aldehyde N-tosylhydrazones was developed. The N-Ts-hydrazones used were prepared in situ via the reactions of 2'-alkynyl-biaryl-2-aldehydes and TsNHNH2(p-methylbenzenesulfonohydrazide). Two types of signals related to the hydrogen bonds, forming in several products, were observed in the 1H NMR spectra recorded in DMSO-d6, assigned to N-H bonds in their dimeric species of product and tautomer.

Copper(I)-Catalyzed Syntheses of Benzo[b]fluorenes by the Cascade Reactions of 2-Alkynylbenzaldehyde N-Tosylhydrazones and Aromatic Terminal Alkynes

Benzo[b]fluorenes were synthesized via CuI-catalyzed cascade reactions of 2-alkynylbenzaldehyde N-tosylhydrazones and aromatic terminal alkynes in the presence of base including the formation of the benzoenyne-allene intermediate in situ and its Schmittel cyclization. Density functional theory calculation was performed to give the energy difference for the formation of 5-phenyl-11H-benzo[b]fluorene and 1,2-diphenyl-1H-cyclobuta[a]indene from the proposed diradical intermediates.

Isoquinolone Synthesis via Zn(OTf)2-Catalyzed Aerobic Cyclocondensation of 2-(1-Alkynyl)-benzaldehydes with Arylamines

A zinc(II) triflate-catalyzed cyclocondensation of ortho-alkynylbenzaldehydes with arylamines in the presence of base under an oxygen atmosphere affording isoquinolones in good to high yields has been developed. The advantages of the present catalyst system include the use of an air-stable and cheap commercially available Lewis acid as the catalyst, high atom utilization and easily available starting materials.

Quinazolinone Synthesis through Base-Promoted SNAr Reaction of ortho-Fluorobenzamides with Amides Followed by Cyclization

A transition-metal-free synthesis of quinazolin-4-ones by Cs2CO3-promoted SNAr reaction of ortho-fluorobenzamides with amides followed by cyclization in dimethyl sulfoxide has been developed. The present procedure can provide efficient synthetic methods for the formation of both 2-substituted and 2,3-disubstituted quinazolin-4-one rings depending on the use of easily available starting materials and an efficient, one-pot protocol for the synthesis of the marketed drug product of methaqualone.

Electrochemically modified Corey-Fuchs reaction for the synthesis of arylalkynes. The case of 2-(2,2-dibromovinyl)naphthalene

The electrochemical reduction of 2-(2,2-dibromovinyl)naphthalene in a DMF solution (Pt cathode) yields selectively 2-ethynylnaphthalene or 2-(bromoethynyl)naphthalene in high yields, depending on the electrolysis conditions. In particular, by simply changing the working potential and the supporting electrolyte, the reaction can be directed towards the synthesis of the terminal alkyne (Et₄NBF₄) or the bromoalkyne (NaClO₄). This study allowed to establish that 2-(bromoethynyl)naphthalene can be converted into 2-ethynylnaphthalene by cathodic reduction.