Synthesis of substituted 8H-benzo[h]pyrano[2,3-f]quinazolin-8-ones via photochemical 6π-electrocyclization of pyrimidines containing an allomaltol fragment

• Constantine V. Milyutin,
• Andrey N. Komogortsev,
• Boris V. Lichitsky,
• Mikhail E. Minyaev and
• Valeriya G. Melekhina

Beilstein J. Org. Chem. 2023, 19, 778–788, doi:10.3762/bjoc.19.58

• -1,2-diketone [21][22][23][24][25]. However, the direction of the transformation in each case depends on the structure of the bridge fragment. Thus, for example, the 1,3,5-hexatriene cyclization does not occur for pyrazole 1 and imidazole 2 derivatives, and the obtained products are formed exclusively

A study of the photochemical behavior of terarylenes containing allomaltol and pyrazole fragments

• Constantine V. Milyutin,
• Andrey N. Komogortsev,
• Boris V. Lichitsky and
• Valeriya G. Melekhina

Beilstein J. Org. Chem. 2022, 18, 588–596, doi:10.3762/bjoc.18.61

• -induced contraction of the pyranone ring will proceed under UV irradiation. At first, pyrazole 12a was selected as a model object for the investigation of this hypothesis. It was shown that the photoreaction of pyrazole 12a regiospecifically led to the formation of α-hydroxy-1,2-diketone 14a (Scheme 3

• pyranone ring proceeds under UV irradiation of compound 12a, while the 6π-electrocyclization products were not detected in the reaction mixture. However, it should be mentioned that the resulting α-hydroxy-1,2-diketone 14a has a relatively low stability and storing of the NMR sample of compound 14a in

• darkness at room temperature for 5 days resulted in complete decomposition. Despite the labile nature of α-hydroxy-1,2-diketone 14a we attempted to isolate this product in pure form. It should be noted that in contrast to the methylated derivative 16, pyrazole 12a has a low solubility in most organic

An overview on disulfide-catalyzed and -cocatalyzed photoreactions

• Yeersen Patehebieke

Beilstein J. Org. Chem. 2020, 16, 1418–1435, doi:10.3762/bjoc.16.118

• of visible light, oxygen, and disulfide [15]. The diaryl-1,2-diketone products can serve as an important structural component of many natural products and bioactive molecules. This method works for a broad range of substrates with high yields (77–97%). A plausible mechanism for this reaction is that

The LANCA three-component reaction to highly substituted β-ketoenamides – versatile intermediates for the synthesis of functionalized pyridine, pyrimidine, oxazole and quinoxaline derivatives

• Tilman Lechel,
• Roopender Kumar,
• Mrinal K. Bera,
• Reinhold Zimmer and
• Hans-Ulrich Reissig

Beilstein J. Org. Chem. 2019, 15, 655–678, doi:10.3762/bjoc.15.61

• OX17. This sequence demonstrates the potential of the C-5 functionalized oxazoles to be used for further transformations (see below). The examples collected in Table 6 show a dichotomy of oxazole and 1,2-diketone formation that is not fully understood so far. As mentioned above, the presence of bulky

• substituents R2 (and R3) seems to be a prerequisite of the 1,2-diketone formation, however, for the series with R2 = phenyl the observed product distributions are not easy to explain (Table 6, entries 18–23). Nevertheless, a plausible mechanism is presented in Scheme 24 showing the analogy to the Gabriel

• alternative to the strongly acidic conditions, palladium-catalyzed hydrogenolysis of the benzyloxy-substituted derivatives is possible, thus avoiding the condensation to oxazoles. Scheme 25 shows the conversion of KE52 into 1,2-diketone DK14 (compare entry 3 of Table 6). Longer reaction times lead to a

NHC-catalyzed cleavage of vicinal diketones and triketones followed by insertion of enones and ynones

• Ken Takaki,
• Makoto Hino,
• Akira Ohno,
• Kimihiro Komeyama,
• Hiroto Yoshida and
• Hiroshi Fukuoka

Beilstein J. Org. Chem. 2017, 13, 1816–1822, doi:10.3762/bjoc.13.176

• recently obtained by the dimsyl anion-promoted double acylation of enones with benzils, followed by dehydrogenation of the resulting alkanes in one pot [16]. Moreover, if the reaction of cyclic 1,2-diketone I (G = C(O)R1) with activated alkenes may take place similarly, this reaction could be utilized as a

• NHC followed by migration of one neighboring acyl group to the central carbonyl oxygen would generate bisacylated Breslow intermediate 10 (Scheme 5). If this species behaves in a similar manner as the monoacylated intermediate C derived from 1,2-diketone 1, its reaction with enone 6a would be expected

α-Acetoxyarone synthesis via iodine-catalyzed and tert-butyl hydroperoxide-mediateded self-intermolecular oxidative coupling of aryl ketones

• Liquan Tan,
• Cui Chen and
• Weibing Liu

Beilstein J. Org. Chem. 2017, 13, 1079–1084, doi:10.3762/bjoc.13.107

• and TBHP [24][25]. An I−/I2 redox cycle promotes tert-butoxyl and tert-butylperoxyl radical formation from TBHP [26][27][28]. In the presence of TBHP and I2, α-iodoaryl ketones 5 and 6 are oxidized to a 1,2-diketone intermediate 7 and an α-carbonyl radical 9, which can be further transformed to tert

Recent applications of the divinylcyclopropane–cycloheptadiene rearrangement in organic synthesis

• Sebastian Krüger and
• Tanja Gaich

Beilstein J. Org. Chem. 2014, 10, 163–193, doi:10.3762/bjoc.10.14

• , which underwent DVCPR under these conditions to give tetracycle 244 in 50% yield. Matsubara and coworkers [202] investigated the formation of cyclohepta-1,3-diones from 1,2-diketone starting materials. Treatment of 245 with bis(iodozincio)methane resulted in the formation of cis-divinylcyclopropane 246

Synthesis and photooxidation of styrene copolymer bearing camphorquinone pendant groups

• Branislav Husár,
• Norbert Moszner and
• Ivan Lukáč

Beilstein J. Org. Chem. 2012, 8, 337–343, doi:10.3762/bjoc.8.37

• formed in irradiated films of styrene copolymers with pendant BZ groups leads to crosslinking, only small molecular-weight changes in irradiated MCQ/S were observed. Keywords: camphorquinone; 1,2-diketone; (±)-10-methacryloyloxycamphorquinone; photooxidation; polystyrene; Introduction Camphorquinone