6,6-Dicyanopentafulvenes: Electronic Structure and Regioselectivity in [2 + 2] Cycloaddition–Retroelectrocyclization Reactions

Abstract

We present an investigation of the electronic properties and reactivity behavior of electron-accepting 6,6-dicyanopentafulvenes (DCFs). The electron paramagnetic resonance (EPR) spectra of the radical anion of a tetrakis(silylalkynyl) DCF, generated by Na metal reduction, show delocalization of both the charge and unpaired electron to the nitrogens of the cyano moieties and also, notably, to the silicon atoms of the four alkynyl moieties. By contrast, in the radical anion of the previously reported tetraphenyl DCF, coupling to the four phenyl rings is strongly attenuated. The data provide physical evidence for the different conjugation between the DCF core and the substituents in both systems. We also report the preparation of new fulvene-based push-pull chromophores via formal [2 + 2] cycloaddition-retroelectrocyclization reaction of DCFs with electron-rich alkynes. Alkynylated and phenylated DCFs show opposite regioselectivity of the cycloaddition, which can be explained by the differences in electronic communication between substituents and the DCF core as revealed in the EPR spectra of the radical anions.

Rhodium-Catalyzed Dehydrogenative Coupling of Phenylheteroarenes with Alkynes or Alkenes

“…2, 121.3, 123.6, 127.2, 127.7, 127.9, 128.1, 128.7, 129.7, 131.4, 133.2, 134.67, 134.69, 137.2, 137.9, 139.0, 141.0, 143.7, 148. 4, 122.2, 126.3, 127.2, 127.60, 127.65, 127.8, 128.1, 129.8, 131.4, 131.8, 133.7, 134.3, 135.0, 136.8, 138.9, 143.6, 143.8, 152. (dd, J = 1.6, 4.0 Hz, 1H); 13 C NMR (100 MHz, CDCl 3 ) δ 120. 9, 121.8, 122.9, 126.3, 126.7, 127.0, 127.4, 127.7, 127.9, 128.0, 128.4, 129.9, 131.5, 133.3, 134.4, 134.7, 134.9, 135.9, 138.3, 139.5, 140.2, 144.7, 150.9 2, 125.7, 126.9, 127.6, 129.2, 129.7, 130.1, 133.0, 137.4, 140.4, 143.5, 166 1, 126.5, 127.5 (overlapped), 127.6, 127.9, 128.7, 129.4, 129.7, 129.9, 135.75, 135.77, 137.5, 141.3; HRMS m/z Calcd for C 18 2, 123.5, 125.1, 126.0, 126.4, 126.9, 127.3, 127.5, 129.3, 129.4, 129.7, 129.9, 134.8, 135.6, 135.9, 137.4, 141.4; HRMS m/z Calcd for C 19 Hz, 1H); 13 C NMR (100 MHz, CDCl 3 ) δ 31. 3, 34.6, 123.6, 125.1, 125.6, 126.1, 126.3, 127.2, 127.4, 127.5, 129.4, 129.5, 129.9, 134.8, 135.6, 136.0, 141.4, 150.7 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 29 = 1.6, 5.…”

Azulene‐Based Donor–Acceptor Systems: Synthesis, Optical, and Electrochemical Properties

“…[38] Sequential [2+ +2] CA-RE Reaction of 1-Azulenylbutadiynes with TCNE and TTF In 1991, Hopf et al reported the formal [2+ +2] CA-RE reaction of tetrathiafulvalene (TTF) with electron-deficient alkynes with dicyanoethylene substituents in the formation of 1,2-bis(1,3-dithiol-2-ylidene)ethane derivatives with donor-acceptor structures. [42] In regard to the electrochemical analysis, TCBD-TTF adduct 13 showedao ne-stage oxidation wave (+ 0.57 V) in CV owing Table 2. [40] Inspired by this research, we examined the reactiono fb utadiyne derivatives possessing terminal 1-azulenyl groups.…”

Predicting reduction potentials of 1,3,6‐triphenyl fulvenes using molecular electrostatic potential analysis of substituent effects

“…Recently first metallocene‐pentafulvene type complexes are synthesized and characterized . Although these studies demonstrate fulvene as an excellent functional molecule, the possibility of fulvene chemistry is not yet fully unravelled …”