Divergent Synthesis of Densely Substituted Arenes and Pyridines via Cyclotrimerization Reactions of Alkynyl Triazenes

Abstract

Densely functionalized fused aromatic triazenes can be prepared by [2 + 2 + 2] cyclotrimerization reactions of 1alkynyl triazenes. The Cp*Ru-catalyzed cyclization proceeds well both with simple alkynyl triazenes and tethered 1-diynyl triazenes. Attractively, the methodology can be extended to pyridine synthesis by replacing an alkyne with a nitrile. The reaction is regioselective and yields the sterically more hindered product. The triazene group precisely installed on the synthesized aryl and pyridyl ring is a highly versatile moiety, which is effortlessly converted into the most important and frequently used functional aryl substituents, including fluorides. It is also suited for intramolecular transformations to afford a variety of valuable heterocycles. The coordination chemistry of alkynyl triazenes and Cp*RuCl was studied, and led to the structural characterization of a Cp*RuCl(η 2-alkyne) complex, a Cp*RuCl(η 4-cyclobutadiene) complex, and an unusual dinuclear Ru complex with a bridging tetramethylfulvene ligand. Complexes of this type are potentially involved in catalyst deactivation pathways. 9 tional complexes. These species may be linked to catalyst deactivation and can provide some guidance to design even better performing catalysts. ASSOCIATED CONTENT Supporting Information Synthetic procedures, characterization data for all new compounds. This material is available free of charge via the Internet at http://pubs.acs.org.

Synthesis of Indenyl Triazenes by Rhodium‐Catalyzed Annulation Reactions

“…Compound 1i does not feature acidic protons, and we thus attempted a displacement of the triazene by fluoride using HF · pyridine ,. [10a] However, as main products of the reaction, we observed alkyne 10 along with minor amounts of indenone 11 (Scheme ).…”

“…Most of the 1‐alkynyltriazenes used in this study have already been reported, and they were prepared as described in the literature , ,. [10a], For 1‐((3,3‐dimethylbut‐1‐yn‐1‐yl)diazenyl)pyrrolidine and 3,3‐diisopropyl‐1‐(mesitylethynyl)triaz‐1‐ene, the synthetic method was adapted from a published procedure …”

“…An interesting alternative for synthesizing vinyl triazenes are metal‐catalyzed addition reactions to alkynyl triazenes (Scheme c) , , . In collaboration with the Cramer group, we have shown that polycyclic vinyl triazenes can be prepared by Ru‐catalyzed [2+2] cycloaddition reactions of alkynyl triazenes and bicyclic alkenes .…”

Transition‐Metal‐Mediated/Catalyzed Synthesis of Pyridines, Pyrimidines, and Triazines by [2+2+2] Cycloaddition Reactions

“…The [2 + 2 + 2] cycloaddition of an alkynyltriazene and nitrile in the presence of 5 mol% [Cp*Ru] was reported in 2019 by Cramer's group. [28] In this reaction, the cycloaddition proceeds regioselectively with Cp*Ru(MeCN) PF (10 mol%)/Bu 4 NI (16 mol%) (Scheme 28). The Cp*Ru(MeCN) 3 PF 6 system was effective in the reactions of triazenyldiynes and various nitriles to give pyridyl triazenes 72-77 with good regioselectivity.…”

Conversion of anilines to chiral benzylic amines via formal one-carbon insertion into aromatic C–N bonds

“…However, the direct cleavage of aromatic carbon–nitrogen bonds is challenging due to the particularly inert and stable nature of these bonds 22 , 23 . Although aromatic carbon–nitrogen bonds can be activated by converting anilines to more reactive intermediates such as aryldiazonium salts 24 – 27 , arylammonium salts 28 – 30 , amides 31 , 32 , or triazenes 33 , the nitrogen atom is usually discarded in byproducts (Fig. 1b ).…”