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

Abstract

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 5phenyl-11H-benzo[b]fluorene and 1,2-diphenyl-1H-cyclobuta[a]indene from the proposed diradical intermediates.

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

“…Based on our previous studies on the use of N-tosylhydrazones in cyclizations [31][32][33], herein we report a one-pot synthetic method towards 3-substituted 1H-dibenzo[e,g]indazoles (2) from 2 ′ -alkynyl-biaryl-2-aldehyde N-tosylhydrazones, which was then optimized to a one-pot two-steps manner starting from 2 ′ -alkynyl-biaryl-2-aldehydes (1) (Scheme 1c). In addition, in order to explain the observed two types of N-H signals in the 1 H NMR spectra in DMSO-d 6 , the formation of dimeric species is proposed, which is supported by the X-ray structure of one product with the studies of DFT (density functional theory) calculations using the Gaussian 09 program [34] with an SMD solvation model [35].…”

Copper(I)‐Catalyzed Reactions of 2’‐Cyano‐biaryl‐2‐aldehyde N‐Tosylhydrazones with Terminal Alkynes: An Approach towards 9‐Amino‐10‐alkynylphenanthrene Modules

“…Simultaneously, 9‐benzylphenanthrenes could also be obtained from o ‐formyl biphenyl N ‐tosylhydrazones via coupling with terminal alkynes catalyzed by CuBr 2 [10b] (Scheme 1, b). In our previous work, a new synthetic method for the construction of benzo[ b ]fluorene ring has been developed, involving a Cu(I)‐catalyzed formation of benzoenyne‐allene intermediate in situ by the reaction of 2‐alkynylbenzaldehyde N ‐tosylhydrazones with aromatic terminal alkynes [10i] . Thus in this study,we designed a Cu(I)‐catalyzed cascade strategy for one‐pot access to 9‐amino‐10‐alkynylphenanthrenes from the reactions of 2’‐cyano‐biaryl‐2‐aldehyde N ‐tosylhydrazones with terminal alkynes via an allene‐intermediate formed in situ , and followed a 6‐ exo ‐ dig cycloaromatization (Scheme 1, c).…”