Polyaromatic Ribbons from Oligo-Alkynes via Selective Radical Cascade: Stitching Aromatic Rings with Polyacetylene Bridges

Abstract

Selective radical generation in conjugated oligomeric o-aryleneethynylenes initiates an intramolecular cascade which involves five fast radical cyclizations followed by aromatization via a 1,5-H shift with a >93% yield per step. This radical cascade transformation opens a new avenue for the systematic and controlled preparation of functionalized graphene nanoribbons where, potentially, each of the peripheral aromatic rings can be different.

How to Lose a Bond in Two Ways ― The Diradical/Zwitterion Dichotomy in Cycloaromatization Reactions

“…As a continuation of our work on cascade alkyne cyclizations,39,79 we reported that the Au‐catalyzed cyclizations of enediynes can be used for the development of “all endo ‐selective” cascades,80 which are complementary to the “all‐ exo ” radical transformations of tri‐ and tetraalkynes39,81 developed according to the revised rules for alkyne cyclization reactions36 (Scheme ).…”

Eaton’s Reagent‐Mediated Domino π‐Cationic Arylations of Aromatic Carboxylic Acids to Iasi‐Red Polymethoxylated Polycyclic Aromatic Hydrocarbons: Products with Unprecedented Biological Activities as Tubulin Polymerization Inhibitors

“…[11b] Given the interest in these polycondensed systems, several synthetic approaches for the elaboration of PAH skeletons as well as for their peripheral modifications have been developed. [14] The most generally used methodologies for the construction of the PAH framework include: 1) intramolecular and intermolecular Diels-Alder cycloaddition, [15] 2) selective radical cascade cyclization of polyalkynes, [16] 3) flash-vacuum pyrolysis (FVP) of vinyl compounds, [14] 4) intramolecular photocyclization of stilbene-type compounds, [14] 5) ring-closing olefin metathesis (RCM), [14] 6) acid-catalyzed benzannulation and electrophilic cyclization, [14] 7) Lewis-acid promoted oxidative cyclodehydrogenation, [14] 8) Pd-catalyzed cyclization in tandem or not with other transformations, [17] 9) decoration of PAHs by direct CÀH arylation with alkyl and aryl systems, [18] and 10) the very popular and efficient Friedel-Crafts reaction. [11b, 19] Our contribution to this area started from an interesting serendipitous observation we made during the execution of one of our research projects concerning the elaboration of new inhibitors of tubulin polymerization, analogous to the potent combretastatin A4 [20] (CA-4; 3 a) and phenstatin (4 a; Figure 1 and Scheme 1).…”

A DFT study on a mutipathways, one product reaction: Initially divergent radical reactions reconverge to form a single product

“…In a multichannels reaction, there are two or more major products in general. It is always thought that if there is no selectivity in the initially divergent step, the overall reaction will not be selective . As illustrated in Scheme , when two diastereotopic groups X and X′ exist in the precursor, they will convert into different substituents A and B in the initially divergent step.…”

“…It is always thought that if there is no selectivity in the initially divergent step, the overall reaction will not be selective. [1][2][3] As illustrated in Scheme 1, when two diastereotopic groups X and X 0 exist in the precursor, they will convert into different substituents A and B in the initially divergent step. In such reaction, a long corollary is that the divergent step, that is, conversion of either X or X 0 to A, controls the stereoselectivity of the reactions completely.…”