Synthesis of Dibromobenzobarrelene Derivatives and Catalytic Activity of Their Rhodium Complexes

Abstract

A novel synthetic route based on [4+2] cycloaddition for dibromobenzobarrelene derivatives starting from in situ generated 3,5‐dibromo‐1,2‐didehydrobenzene and mesitylene, 1,2,4,5‐tetramethylbenzene, 1,2,3,5‐tetramethylbenzene, pentamethylbenzene, 1,3‐dimethoxybenzene, and 2,4,6‐trimethylbromobenzene, respectively, was developed. Thus, six novel dibromobenzobarrelenes with diverse substitution patterns at the barrelene framework including chiral derivatives are reported. The benzobarrelene 6,8‐dibromo‐1,3,10‐trimethyl‐1,4‐dihydro‐1,4‐ethenonaphthalene (1a) was functionalized at the annulated benzene ring to give three novel carboxylic acids and two novel phosphonic acid esters. Selected benzobarrelene complexes with RhICl were tested for their catalytic activity in the 1,4‐addition of phenylboronic acid towards cyclohex‐2‐enone. Turnover frequencies up to 3405 h–1 were observed, which are among the highest reported so far for Rh–diene complexes in this type of C–C coupling reaction.

Accurate Crystal Structures of C12H9CN, C12H8(CN)2, and C16H11CN Valence Isomers Using Nonspherical Atomic Scattering Factors

“…The C6A-C6B bond length in 4 is sufficiently short as to make it an outlier, and it has therefore been excluded from the combined average. 2a,2b,8b,8c-Tetrahydro-cyclopropa [3,4] 2c) is a direct naphtho-fused analogue to 4 and one of two exemplars in this study with the extended annulene. It is the first structure of its kind to be reported.…”

“…Benzobarrelenes are particularly suited as chelating bis-η 2 -ethene ligands for low-valent transition metals such that more than 70% of the 117 reported crystal structures in the Cambridge Structure Database (CSD, version 2021.2) are of such complexes. Schlesinger et al devised synthetic strategies for an impressive range of partially halogenated benzobarrelene derivatives, which can then be further functionalized . Rhodium complexes of such benzobarrelenes are highly efficient catalysts for 1,4-addition of phenylboronic acid to 2-cyclohexen-1-one.…”

“…Schlesinger et al devised synthetic strategies for an impressive range of partially halogenated benzobarrelene derivatives, which can then be further functionalized. 3 Rhodium complexes of such benzobarrelenes are highly efficient catalysts for 1,4-addition of phenylboronic acid to 2-cyclohexen-1-one. Marder et al have developed a hexadehydro-Diels−Alder (HDDA) reaction in which substituted benzobarrelenes and barrelene-like compounds with extended ring systems can be synthesized from a benzyne-trapping reaction with an aromatic reagent (benzene, toluene, anthracene).…”

“…2a,2b,6b,6c-Tetrahydrobenzo(a)cyclopropa(ca)pentalene-6C-carbonitrile, 4, crystallizes in P2 1 2 1 2 1 with Z′ = 1 and bears the nitrile substituent at the central apical sp 3 site C6C. In dinitrile variant 2a,2b,6b,6c-tetrahydrobenzo(a)cyclopropa(ca)pentalene-1,2dicarbonitrile, 11 (Pbca, Z′ = 2), the cyano groups are located on sp 2 C atoms of the cage edge rather than the apical sp 3 . It crystallizes with two ordered molecules in the asymmetric unit which have very similar geometries, the dimensions of which are presented comparatively in Table 2 (as 11 1 and 11 2 ); only one is shown in Figure 2b.…”

“…There is continuing strong interest in the preparation and applications of benzobarrelenes (1,4-dihydro-1,4-ethenonaphthalenes, I in Chart ), − which are derivatives of the parent barrelene (bicyclo[2.2.2]­octa-2,5,7-triene) first reported by Zimmerman in 1960 . Benzobarrelenes are particularly suited as chelating bis-η 2 -ethene ligands for low-valent transition metals such that more than 70% of the 117 reported crystal structures in the Cambridge Structure Database (CSD, version 2021.2) are of such complexes.…”