Palladium‐Catalyzed Benzofulvenation of o‐Arylanilines through C−H Bond Activation by Using Two Diarylacetylenes as an Implicit Benzofulvene

Abstract

We report the first example of Pd(II)catalyzed highly step-and atom-economical benzofulvenation through free amine-directed ortho CÀH bond activation of o-arylanilines. This paper presents a novel, simple, and efficient approach for the synthesis of benzofulvene derivatives from oarylaniline substrates through CÀH bond activation with two diarylacetylenes as an implicit benzofulvene unit. The reactivity of synthesized benzofulvenes toward oxidation was investigated, and they were shown to transform into phenanthridines, oxabenzofulvenes, and fluorescent polycyclics.

Transition Metal Catalyzed Free‐Amine (−NH2) Directed C−H Bond Activation and Functionalization for Biaryl Frameworks

“…A variety of symmetrical and unsym- In 2018, Chuang and co-workers unfolded a new reactivity paradigm of Pd(II)-catalyzed free-amine directed one-pot twofold CÀ H bond activation protocol to expedite the access of benzofulvenated o-arylaniline skeletons (Scheme 24a). [31] A combination of Pd(OAc) 2 as catalyst and Cu(OAc) 2 as an oxidant in dichloromethane solvent was effective for coupling of various internal alkynes and substituted 2-arylanilines in a cascade mode. The reaction is very general with wide substrate scope.…”

TfOH-promoted Classical Nazarov-type Cyclization of Benzofulvenes: Synthesis of Polycyclic 5H,10′H-spiro[benzo[k]phenanthridine-5,6′-dibenzopentalenes]

“…It was noteworthy that azulenes were observed in low yields (<5%) under the optimized condition in cases of 1h – 1j . These azulenes were formed through another reaction pathway at lower temperature . Notably, our reaction conditions were well suited for the substituted methoxy ( 1k ) and fluoro ( 1l ) on the o -benzofulvenyl moiety, thus producing moderate yields of the corresponding intramolecular cyclization products 2k / 2k′ and 2 / 2l′ (47% and 54%) with diastereomeric ratios of 79:21 and 76:24, respectively.…”

“…These reactions usually involve protonation and the formation of carbocation to induce intramolecular cyclization. We demonstrated that the compound ( Z )-2-(2-((2,3-diphenyl-1 H -inden-1-ylidene)­(phenyl)­methyl)­naphthalen-1-yl)-5-methylanilines ( 1a ) undergoes intramolecular rearrangement in the presence of TfOH, yielding polycyclic 5- and 7-membered azulene cores . We herein present a simple and metal-free mild condition for the synthesis of 5 H ,10′ H -spiro­[benzo­[ k ]­phenanthridine-5,6′-dibenzopentalenes] through intramolecular cyclization of 1a in the presence of TfOH (Scheme d).…”

“…We demonstrated that the compound (Z)-2-(2-((2,3-diphenyl-1H-inden-1-ylidene)(phenyl)methyl)naphthalen-1-yl)-5-methylanilines (1a) undergoes intramolecular rearrangement in the presence of TfOH, yielding polycyclic 5-and 7-membered azulene cores. 22 We herein present a simple and metal-free mild condition for the synthesis of 5H,10′H-spiro[benzo[k]phenanthridine-5,6′-dibenzopentalenes] through intramolecular cyclization of 1a in the presence of TfOH (Scheme 2d). We found that the tethered naphthalene ring in 1 enhanced the electron delocalization to promote the formation of desired compounds 2, which were not applicable in our previous study.…”

Selective Synthesis of Dihydrophenanthridine and Phenanthridine Derivatives from the Cascade Reactions of o-Arylanilines with Alkynoates through C–H/N–H/C–C Bond Cleavage

“…Chuang et al. disclosed a Pd-catalyzed benzofulvenation of o -arylanilines through C–H bond activation by using two diaryl acetylenes as an implicit benzofulvene (Scheme c) . Baidya et al.…”