Exceptionally short central bonds in the cumulogue and the vinylogue of 2,2-dicyano-1,1-bis(dimethylamino)ethylene

Abstract

The preparation and crystal structures of twofold push-pull butatriene 2-cyano-5,5-bis(dimethylamino)penta-2,3,4-trienentrile 9 and butadiene 2-cyano-5.5-bis(dimethylamino) penta-2.4-dienenitrile 4 with bis-dimethylamino and dicyano substituents are described. These compounds may be compared with the known corresponding ethylene derivative 1 ,I -dicyano-2,2-bis(dimethy1amino)ethylene 5. The exceptionally short central bonds in 9 and 4 are in agreement with the earlier proposed concept of cumulogy and of vinylogy to 5.Vinylogous activation of the methyl group by cyano substituents is much stronger than by ester substituents.' Thus, et hylidenemalononitrile I condenses with N,N-dimethyldichloromethyleneaminium chloride 22 to the new 2-chloro dienamine 3 whereas the diester analogue fails to react.' The substitution of the chlorine atom in 3 with N,N-dimethylamine leads to the twofold push-pull butadiene 43 (Scheme 1). Compound 4 is the vinylogue4 of the known I,l-dicyano-2,2bis(dimethy1amino)ethylene 5 (Scheme 2).

Push–Pull Buta‐1,2,3‐trienes: Exceptionally Low Rotational Barriers of Cumulenic CC Bonds and Proacetylenic Reactivity

“…The two extremes are symmetric, electronically neutralc umulenes (average BLA = 0.10 ) [6] and polarized ones (highest reported BLA = 0.18 ). [13] All new [3]cumulenes reported here display significant BLA. Likewise, the strength of electron donor and acceptor have an impact on the BLA of the [3]cumulene inserted between them.…”

“…Compounds 3a-c were synthesized in good yields using the previously reported route to polarized [3]cumulenes, [7,13,14,21] by addition of electron-rich terminal olefins 5a,b to the electronpoor 1,1-dichloroethene derivatives 6a,b, [22] followed by dehydrohalogenation in ao ne-pot reaction (Scheme 1). The symmetric olefin 5a was synthesized from Michler's ketone by reaction with methylmagnesium bromide.…”

“…[12] Upon polarization of [3]cumulenes by donors and acceptors at the terminal Ca toms, the BLA increases significantly,w ith the central C=Cb ond adopting nearly the length of an acetylenic bond, around1 .21 . [7,13] In ap reliminaryc ommunication, [14] we showed that the central C=Cb ond in push-pullsubstituted [3]cumulene 1,w ith al ength of 1.22 , indeed features characteristic acetylenic reactivity,i na ddition to olefinic reactivity. [15] Similart od onor-polarized alkynes, 1 reacteda t room temperature with tetracyanoethene (TCNE) in af ormal [2+ +2] cycloaddition-retroelectrocyclization (CA-RE) [16] reaction to give the stable zwitterionic tetracyanobuta-1,3-diene 2 as the exclusive product ( Figure 1).…”

“…decomp. ); 1 HNMR (500 MHz, C 2 D 2 Cl 4 ,2 58 C) d = 1.49 (d, J = 6.9 Hz, 12 H; 4C HCH 3 ), 3.35 (s, 6H;2NCH 3 ), 3.78 (s, 3H;O CH 3 ), 4.31 (sept, J = 6.9 Hz, 2H;2NCH), 6.90 (d, J = 9.3 Hz, 2H;H -C(3'',5'')), 7.06 (d, J = 9.5 Hz, 2H;H -C(3'',5'')), 7.61-7.42 ppm (m, 4H;2H-C(2'',6''));13 CNMR (101 MHz, C 2 D 2 Cl 4 ,2 58 C; 1:1m ixture of stereoisomers) d = 20.81 (2 CHCH 3 ), 41.03 (2 NCH 3 ), 50.84 (OCH 3 ), 52.29 (2 NCH), 78.30 (C(1')), 111.61 (2 CN), 112.33 (2 CN), 114.22 (C(3'',5'')), 115.95 (2 CN), 117.28 (C(3'',5'')), 117.72 and 118.27 (C(1'')), 129.44 and 130.18, 140.16 (2 C(2'',6'')), 156.35 (2 C(4'')), 158.69 and 160.26, 166.05 and 166.77 ppm (C=O);3Ch idden by the noise;I R( ATR): ñ = 2974 (w), 2206 (m), 2191 (s), 1678 (s), 1614 (m), 1577 (s), 1524 (m), 1456 (s), 1433 (s), 1382 (s), 1336 (S), 1308 (m), 1272 (s), 1198 (s), 1159 (m), 1114( s), 1007 (w), 938 (m), 912 (s), 859 (w), 831 (s), 814 (m), 791 (w), 780 (w), 764 (w), 741 (w), 682 (s), 653 (w), 627 (w), 613 cm À1 (w);U V/Vis (CH 2 Cl 2 ): l max (e) = 828 (29 500), 457 (22 700), 317 nm (28 400 m À1 cm À1 ); HR-MALDI-MS: m/z (%): 580.…”

2,6‐Di‐tert‐butyl‐4‐(3,3‐diarylpropadienylidene)‐2,5‐cyclohexadien‐1‐ones, the First Stable p‐Quinopropadienes

“…The structural properties account for the higher reactivity of radical anions 2 − · relative to 1 − · . The characteristic points of each of these structures are the short central double bond (C7−C8) and the long side double bonds (C4−C7 and C8−C9); the central double bond of 2a (1.228 Å) is the second shortest among the known butatrienes, the shortest one being the highly polarized 1,1‐dicyano‐4,4‐bis(dimethylamino)butatriene ( 10 ) (1.201 Å) 14. In those structures of low symmetry, the lengths of the side double bonds are different; the quinone methide double bonds (C4−C7) are 0.24Å for 2a and 0.27 Å for 2e longer than the diarylmethylene double bonds (C8−C9).…”