One‐Step Conversion of Aromatic Hydrocarbon Bay Regions into Unsubstituted Benzene Rings: A Reagent for the Low‐Temperature, Metal‐Free Growth of Single‐Chirality Carbon Nanotubes

Abstract

A tube ride: The controlled chemical synthesis of uniform, single‐walled carbon nanotubes from short hydrocarbon templates, such as aromatic belts and geodesic nanotube end‐caps, by a Diels–Alder cycloaddition/rearomatization strategy requires a potent “masked acetylene” capable of transforming hydrocarbon bay regions into new unsubstituted benzene rings in a single operation. Nitroethylene has been found to effect such benzannulations (see scheme).

Extraordinary Transformations to Achieve the Synthesis of Remarkable Aromatic Compounds

“…Whereas the field of total synthesis of natural products can boast many examples of methodology that was invented specifically for application in the synthesis of a particular target, the field of novel aromatics has relatively few. Hopf's biallenyl-based synthesis of [2.2]paracyclophanes (Scheme 6), which underpinned his synthesis of superphane (27), immediately springs to mind as one such case. At the same time, it would be unfair to characterize synthetic endeavors in the novel aromatics arena as being essentially reliant upon existing methodology.…”

“…The reaction leading to 24 is also noteworthy in that it kicks off Hopf's synthesis of superphane (27), [23] which came very shortly on the heels of Boekelheide's landmark synthesis ( Figure 3). [24,25] Whereas Hopf's synthesis relied heavily on intramolecular carbene insertion reactions to build the final four bridges, Boekelheide's synthesis exploited three [4 + 4] cycloaddition reactions, one intermolecular and two intramolecular.…”

“…Larry Scott, who delivered the inaugural Nozoe lecture at ISNA-9 in Hong Kong, reported an extraordinary Diels-Alder reaction between nitroethene (an unusual dienophile) and bisanthene 31 (a very unusual diene) to afford ovalene derivative 35 (Scheme 8). [27] This chemistry, which allows one to seriously consider the metal-free growth of single chirality carbon nanotubes from small hydrocarbon templates, [28] owes its success to the exceptionally strong dienophilicity of nitroethene, the allowed nature of the thermal [ reported that even ethyne will do the job. [29] More forcing conditions are required, but nothing like those used for carbon nanotube production.…”

Combinatorial approach for the synthesis of precursors for chirality-controlled synthesis of SWCNTs

“…4c. In the same manner, the combinatorial synthesis utilizing ketones K1 and K3 (precursor molecules are not shown) will result in the formation of precursors for 22 chiralities, namely-(6,6), (7,5), (8,4), (9,3), (8,8), (9,7), (10,6), (11,5), (12,4), (10,10), (11,9), (12,8), (13,7), (14,6), (15,5), (12,12), (13,11), (14,10), (15,9), (16,8), (17,7), and (18,6). Correspondingly, the combination of K3 and K2a will give a mixture of 22 precursors for (9,0), (9,1), (9,2), (9,3), (12,0), (12,1), …”

“…Among different approaches to tackle this challenge, the use of template molecules to dictate unambiguously the chirality of the produced SWCNTs seems to be very promising, but until recently has not been fully successful [14][15][16][17][18][19][20][21][22][23][24][25][26][27][28]. Attempts to grow single chirality SWCNTs from welldefined template molecules such as CNT-end-caps [29], and small CNT-rings [30], have shown only selectivity in the CNT diameter distribution, but no control over the tube chirality was achieved, pointing on a skeletal rearrangement in template molecules before the CNT growth initiation.…”