2,1-Bensoidoxazoles [anthranils]. Synthesis and opening of the isoxazole ring (review)
The present review covers the literature on the synthesis of 2,l-benzoisoxazoles (anthranils) (I), and reactions of this bicyclic system which involve opening of the isoxazole ring. Since a detailed and satisfactorily full review of the chemistry of 2, l-benzoisoxazoles was published in 1967 [96], the main thrust of the present review is to cover the literature of the last twenty years. It has nevertheless been necessary to include earlier publications, especially when these deal with general methods of synthesis of anthranils. t i. Synthesis of 2~l-Benzisoxazoles
Die photolyse von Anthranilen in saurer Lösung; Vergleich mit der photochemischen und thermischen Zersetzung entsprechender 2-Azido-acylbenzole in saurer Lösung. Vorläufige Mitteilung†‡
Anthranils 1a, b, 4 und 5 yield on irradiation in cone. sulfuric acid 2-amino-5 hydroxy-acylbenzenes 2a, b, 6 and 7 which are isolated mainly as their acetates. Small amounts of 2-amino-3-hydroxy-acylbenzenes 3a and 3b are formed as by-products (cf. tables 1 and 2). Simila results were obtained when the corresponding 2-azido-acylbenzenes were decomposed thermally i cone. sulfuric acid (cf. tables 1 and 2). 3,5-Dimethylanthranil (8) forms, on irradiation in sulfuric acid and subsequent acetylation, 2-acetamino-5-acetoxy-6-methylacetophenone (6) and 2-acetamino-5-acetoxymethyl-acetophenone (10). The same compounds were obtained from the thermaldecomposition of 2-azido-5-methyl-acetophenone (19) in sulfuric acid.
An Extended Chain and Trinuclear Complexes Based on Pt(II)-M (M = Tl(I), Pb(II)) Bonds: Contrasting Photophysical Behavior.
The syntheses and structural characterizations of a Pt-Tl chain [{Pt(bzq)(C6F5)2}Tl(Me2CO)]n 1 and two trinuclear Pt2M clusters (NBu4)[{Pt(bzq)(C6F5)2}2Tl] 2 and [{Pt(bzq)(C6F5)2}2Pb] 3 (bzq = 7,8-benzoquinolinyl), stabilized by donor-acceptor Pt → M bonds, are reported. The one-dimensional heterometallic chain 1 is formed by alternate "Pt(bzq)(C6F5)2" and "Tl(Me2CO)" fragments, with Pt-Tl bond separations in the range of 2.961(1)-3.067(1) Å. The isoelectronic trinuclear complexes 2 (which crystallizes in three forms, namely, 2a, 2b, and 2c) and 3 present a sandwich structure in which the Tl(I) or Pb(II) is located between two "Pt(bzq)(C6F5)2" subunits. NMR studies suggest equilibria in solution implying cleavage and reformation of Pt-M bonds. The lowest-lying absorption band in the UV-vis spectra in CH2Cl2 and tetrahydrofuran (THF) of 1, associated with (1)MLCT/(1)L'LCT (1)[5dπ(Pt) → π*(bzq)]/(1)[(C6F5) → bzq], displays a blue shift in relation to the precursor, suggesting the cleavage of the chain maintaining bimetallic Pt-Tl fragments in solution, also supported by NMR spectroscopy. In 2 and 3, it shows a blue shift in THF and a red shift in CH2Cl2, supporting a more extensive cleavage of the Pt-M bonds in THF solutions than in CH2Cl2, where the trinuclear entities are predominant. The Pt-Tl chain 1 displays in solid state a bright orange-red emission ascribed to (3)MM'CT (M' = Tl). It exhibits remarkable and fast reversible vapochromic and vapoluminescent response to donor vapors (THF and Et2O), related to the coordination/decoordination of the guest molecule to the Tl(I) ion, and mechanochromic behavior, associated with the shortening of the intermetallic Pt-Tl separations in the chain induced by grinding. In frozen solutions (THF, acetone, and CH2Cl2) 1 shows interesting luminescence thermochromism with emissions strongly dependent on the solvent, concentration, and excitation wavelengths. The Pt2Tl complex 2 shows an emission close to 1, ascribed to charge transfer from the platinum fragment to the thallium [(3)(L+L')MM'CT]. 2 also shows vapoluminescent behavior in the presence of vapors of Me2CO, THF, and Et2O, although smaller and slower than those of 1. The trinuclear neutral complex Pt2Pb 3 displays a blue-shift emission band, tentatively assigned to admixture of (3)MM'CT (3)[Pt(d) → Pb(sp)] with some metal-mediated intraligand ((3)ππ/(3)ILCT) contribution. In contrast to 1 and 2, 3 does not show vapoluminescent behavior.