Diels–Alder Reactions of 9-Ferrocenyl- and 9,10-Diferrocenylanthracene: Steric Control of 9,10- versus 1,4-Cycloaddition

Abstract

Cycloadditions of benzynes, N-methyl-or Nphenylmaleimide, dimethyl acetylenedicarboxylate, and benzoquinone to 9-ferrocenylanthracene (1) and 9,10-diferrocenylanthracene (2) are described. Benzyne and 3-fluorobenzyne add to 1 and 2 to form the corresponding 9-ferrocenyl-or 9,10-diferrocenyltriptycenes; in contrast, bulkier benzynes such as 3-trifluoromethylbenzyne preferentially add to 2 across C 1 and C 4 to form 6,11-diferrocenyl-5,12-etheno-5,12-dihydrotetracenes. The maleimides undergo Diels−Alder reactions with 1 to form the 9-ferrocenylbarrelenes 10 and 11, but cycloaddition to 2 occurs not only across C 9 and C 10 to form the barrelene 13 but also across C 1 and C 4 to yield ethenoanthracenes as both endo and exo adducts, 14 and 15, respectively. Likewise, DMAD forms 11,12-dicarbomethoxy-9-ferrocenylbarrelene (16) with 1 but reacts with 2 by addition across C 1 and C 4 to form 17. Hydrolysis of 16 cleaves only the ester distant from the ferrocenyl group. Treatment of the Diels−Alder adduct 20 of 9-ferrocenylanthracene (1) and benzoquinone with base and RX (R = Me, Et, CH 2 OMe, CH 2 CO 2 Me) yields the corresponding 1,4-dialkoxy-9-ferrocenyltriptycenes 22−25. The factors influencing the regiochemistry of the cycloadditions are discussed, and several examples of each reaction type have been characterized by X-ray crystallography.

Ferrocenyl‐Pyrenes, Ferrocenyl‐9,10‐Phenanthrenediones, and Ferrocenyl‐9,10‐Dimethoxyphenanthrenes: Charge‐Transfer Studies and SWCNT Functionalization

“…The distance between the ferrocenyl cyclopentadienyl ipso ‐carbon atoms and the aromatic units is similar for all investigated compounds (from 1.476(3) Å ( 7 a ) to 1.554(8) Å ( 10 )) and agree well with literature values …”

“…The distance between the ferrocenyl cyclopentadienyl ipsocarbon atoms and the aromatic units is similar for all investigated compounds (from 1.476(3) (7a)t o1 .554(8) (10)) and agree wellwith literature values. [2,6,8,15,[47][48][49] In Tables SI3 and SI4 (in the Supporting Information), the bond lengths of the different aromatic cores are summarized. The substitution pattern does not affect the position of the single and double bonds in the aromatic moieties.…”

A Ferrocenyl Kaleidoscope: Slow Interconversion of Six Diastereo‐atropisomers of 2,6‐Di‐tert‐butyl‐9,10‐diferrocenyltriptycene

“…[13][14][15] Cycloaddition of benzyne to 1 and 2 furnished 9-ferrocenyltriptycene, 3, and 9,10-diferrocenyltriptycene, 4, respectively. Variable-temperature and 2D-EXSY NMR data on 3 straightforwardly yielded a rotational barrier of (16.5 AE 0.5) kcal mol À1 .…”

“…General approach to substituted ferrocenyltriptycenes 3, 4 and 6 from the corresponding anthracenes. [13][14][15] Synthesis of 2,6-di-tert-butyl-9,10-diferrocenyltriptycene, 6, requires repeated treatment of 5 with benzyne followed by separation. cycloaddition proceeded only in modest yield and that the separation of 5 and 6 was tedious.…”

“…[19] We note that, in the current work, 2,6-di-tert-butyl-9,10-diferrocenyltriptycene, 6, is racemic; in principle it could be obtained in enantiomerically pure form. However, despite our previous acquisition of crystallographic data on numerous ferrocenyltriptycenes and -dibenzobarrelenes, [7,[11][12][13][14][15] attempts to acquire X-ray quality crystals of 6 were unsuccessful, possibly because of the presence of so many coexisting rotamers of similar energy.…”