The β-H-elimination in the (iPr)AuEt complex and its microscopic reverse, the insertion of ethene into (iPr)AuH, were investigated in a combined experimental and computational study. Our DFT-D3 calculations predict free-energy barriers of 49.7 and 36.4 kcal mol(-1) for the elimination and insertion process, respectively, which permit an estimation of the rate constants for these reactions according to classical transition-state theory. The elimination/insertion pathway is found to involve a high-energy ethene hydride species and is not significantly affected by continuum solvent effects. The high barriers found in the theoretical study were then confirmed experimentally by measuring decomposition temperatures for several different (iPr)Au(I) -alkyl complexes which, with a slow decomposition at 180 °C, are significantly higher than those of other transition-metal alkyl complexes. In addition, at the same temperature, the decomposition of (iPr)AuPh and (iPr)AuMe, both of which cannot undergo β-H-elimination, indicates that the pathway for the observed decomposition at 180 °C is not a β-H-elimination. According to the calculations, the latter should not occur at temperatures below 200 °C. The microscopic reverse of the β-H-elimination, the insertion of ethene into the (iPr)AuH could neither be observed at pressures up to 8 bar at RT nor at 1 bar at 80 °C. The same is true for the strain-activated norbornene.

A series of indolo[2,3-b]quinoxaline derivatives were efficiently synthesized from 2,3-dibromoquinoxaline by two pathways. A one-pot approach using Pd-catalyzed two-fold C-N coupling and C-H activation reactions gave indolo[2,3-b]quinoxaline derivatives in good yields, but with limited substrate scope. In addition, a two-step approach to indolo[2,3-b]quinoxalines was developed which is based on Pd-catalyzed Suzuki coupling reactions and subsequent annulation by Pd-catalyzed two-fold C-N coupling with aromatic and aliphatic amines. The electrochemical and photochemical properties of indolo[2,3-b]quinoxaline derivatives were investigated. These studies show that 6-(4-methoxyphenyl)-6H-indolo[2,3-b]quinoxaline showed the highest HOMO energy level and lowest band gap.

The genus Glycosmis, family Rutaceae, is a rich source of alkaloids, including those of the quinolone, quinazoline, furoquinoline, acridone, sulphur-containing amides and carbazole types.1,2) Carbazole alkaloids were isolated from the seeds 3) and the roots 4,5) of G. pentaphylla, from the bark of G. mauritiana 6) and G. rupestris, 7) and from the roots of G. arborea. 8) Carbazole alkaloids have also been found in other Rutaceous genera, e.g., Micromelum, Murraya, and Clausena. From two genera, Murraya and Clausena, nearly four fifths of the natural carbazole alkaloids have been isolated.9,10) In a continuing search for bioactive natural products from Vietnamese plants, a number of plants, including species Glycosmis stenocarpa (DRAKE) TAN., have been screened for cytotoxic, antifungal, and antibacterial activities.11,12) G. stenocarpa, local name "com ruou trai hep," is a small shrub, 0.75-1 m high. It is an endemic plant, found in some provinces in north Vietnam.13) This paper reports the isolation and structural elucidation of a new dimeric pyranocarbazole alkaloid, named bisisomahanine (1), and two known monomeric carbazole alkaloids, viz. murrayafoline-A (2) 14) and murrayanine (3), 15) from the roots of G. stenocarpa. Results and DiscussionBisisomahanine (1) was obtained as a pale ivory powder, mp 130-140°C, [a] D 20 Ϫ13.1°. The UV spectrum showed the typical absorbances at 209, 224, and 245 nm, closely similar to those of 2 and 3, and indicative of the carbazole skeleton in 1. Furthermore, it exhibited absorbances at 298 (sharp, strong) and 335 nm (broad, weak), typical of an angular pyranocarbazole unit as described for isomahanine (4). (Table 1) and the peak at m/z 83 in the EI-MS spectrum were assignable to the isohexenyl side chain.16,17) The assignments of carbons at positions C-1Ј and C-2Ј of alkaloid 1 are different than those reported for isomahanine (4), 16) and were confirmed by data from HMQC and HMBC experiments ( Table 1). The HMQC spectrum of 1 showed the direct .1 (C-3Ј), and 22.7 (C-2Ј). The 1 H-1 H COSY and NOESY spectra of 1 also confirmed the above assignment of the isohexenyl side chain (Fig. 1).In the downfield region of the 1 H-NMR spectrum, two broad singlets at d 7.51 and 5.14 were assigned to an NH and a phenolic hydroxyl group, respectively; this was supported by the IR bands at 3470 and 3362 cm Ϫ1, and the fact that no carbons were attached to these proton signals, as shown by the HMQC spectrum. There were two isolated pairs of orthocoupled protons: the first pair at d 6.73 (H-5) and 7.71 (H-6), and the second at d 6.43 (H-1) and 5.54 (H-2). The COSY spectrum confirmed the two separate spin systems. The NMR spectral data of the latter pair were similar to those in some Murraya alkaloids such as isomahanine (4) and mahanine (5), 16) murrayamine C (7), 18) and pyrayafoline-D (6) (assigned the same structure as 4 by Ito et al.), 17) indicating the presence of a pyran ring double bond in the pyranocarbazoletype skeleton of 1.The position of fusion between the pyrano and carbazole ...

A series of 5,10-dihydroindolo[3,2-b]indoles was successfully prepared by an efficient two-step strategy based on site-selective Pd-catalyzed cross-coupling reaction with N-methyl-2,3-dibromoindole and subsequent cyclization by two-fold Pd-catalyzed C-N coupling with amines. The products show a strong fluorescence.