Volatiles from the tropical ascomycete Daldinia clavata (Hypoxylaceae, Xylariales)

• Tao Wang,
• Kathrin I. Mohr,
• Marc Stadler and
• Jeroen S. Dickschat

Beilstein J. Org. Chem. 2018, 14, 135–147, doi:10.3762/bjoc.14.9

• are already defined. A third extension with malonyl-SCoA and methylation gives rise to intermediate C that can be released, e.g., by a thioesterase to the β-keto acid D, followed by spontaneous decarboxylation to 11a. Two structurally related molecules to 11a have been reported from endophytic

Sustainable synthesis of 3-substituted phthalides via a catalytic one-pot cascade strategy from 2-formylbenzoic acid with β-keto acids in glycerol

• Lina Jia and
• Fuzhong Han

Beilstein J. Org. Chem. 2017, 13, 1425–1429, doi:10.3762/bjoc.13.139

• phthalides in good to excellent yields. Conclusion: A concise and efficient synthesis strategy of 3-substituted phthalides from 2-formylbenzoic acid and β-keto acids via a catalytic one-pot cascade reaction in glycerol has been accomplished. Keywords: β-keto acid; decarboxylation; glycerol; one-pot cascade

• 2b–f, both electron-donating and electron-withdrawing groups such as methyl (2b), methoxy (2c), and halogens (2d–f) afforded the products in relatively high reaction yields. The use of meta-aryl substituted β-keto acids provided the products in good yields, whereas β-keto acid 2i, bearing a methyl

• -keto acid bearing a heteroaromatic ring (2k) afforded the desired product in 85% yield. Unfortunately, acetoacetic acid did not undergo the reaction due to its low reactivity. Finally, the substituted 2-formylbenzoic acid 1b (5,6-(OCH3)2) was also tested for this transformation, and the target product

Biosynthesis of α-pyrones

• Till F. Schäberle

Beilstein J. Org. Chem. 2016, 12, 571–588, doi:10.3762/bjoc.12.56

• the catalytic cysteine residue. Subsequently, the thioester bond is cleaved by the nucleophilic water molecule, which itself is activated through hydrogen bonding to the catalytic cysteine and a histidine residue. Thereby, the β-keto acid intermediate is generated. This intermediate is proposed to be

• placed within the novel pocket, a cavity accessible from the conventional elongation/cyclization pocket. After the replacement of the first β-keto acid, the second β-ketoacyl unit is produced. The catalytic cavity of CysB is loaded with a fatty acyl-CoA which is elongated with one molecule of malonyl-CoA

• reaction to form the α-pyrone, while CysB should first generate a β-keto acid intermediate by hydrolysis of the thioester bond. Then the starter of the second chain is loaded onto the free catalytic cysteine, gets elongated by a malonyl-CoA before the nucleophilic attack of the first chain. In that way the

Photo, thermal and chemical degradation of riboflavin

• Muhammad Ali Sheraz,
• Sadia Hafeez Kazi,
• Sofia Ahmed,
• Zubair Anwar and
• Iqbal Ahmad

Beilstein J. Org. Chem. 2014, 10, 1999–2012, doi:10.3762/bjoc.10.208

• , 267, 373 and 444 nm in the UV and visible regions in aqueous solution and is degraded into various photoproducts on exposure to light [1]. These products include formylmethylflavin (FMF), lumichrome (LC), lumiflavin (LF), carboxymethylflavin (CMF), 2,3-butanedione, a β-keto acid and a diketo compound

• photoproducts thus obtained are also dependent on pH. The main photoproducts of RF are FMF and LC which are formed at pH 1–12 and LF at pH 7–12 due to the oxidation of the ribityl side-chain. Along with these major photoproducts some minor products are also formed such as CMF at pH 1–12, and a β-keto acid and a

• the thermal destruction of RF [150][151][152]. Ahmad et al. [153] carried out a study of the thermal degradation of RF at 50–70 °C and identified a β-keto acid and a dioxo compound as the isoalloxazine ring cleavage products at pH 9–13. These authors developed a multicomponent spectrometric method for

A convenient enantioselective decarboxylative aldol reaction to access chiral α-hydroxy esters using β-keto acids

• Zhiqiang Duan,
• Jianlin Han,
• Ping Qian,
• Zirui Zhang,
• Yi Wang and
• Yi Pan

Beilstein J. Org. Chem. 2014, 10, 969–974, doi:10.3762/bjoc.10.95

• investigating different Lewis acids with various chiral PyBox ligands 4–8 (Table 1), we discovered that Sc(OTf)3 and tridentate PyBox ligand 6a could promote the decarboxylative aldol reaction of β-keto acid 1a with α-keto ester 2a in excellent yield with high enantioselectivity in toluene (Table 1, entry 9

• ). Trace amount of side product acetophenone was formed through decarboxylative protonation of β-keto acid 1a, which was commonly observed in the case of chiral organic base catalysed decarboxylative additions. Further optimisation of the reaction conditions showed that CHCl3 was the best solvent choice in

• enolates. Though in the case of enzymatic reactions, decarboxylation occurs first to form the enolates, followed by condensation with esters; it is believed that in the scandium-catalysed aldol process of β-keto acid, similar to the case of malonic acid half thioesters, decarboxylation happens after the

The myxocoumarins A and B from Stigmatella aurantiaca strain MYX-030

• Tobias A. M. Gulder,
• Snežana Neff,
• Traugott Schüz,
• Tammo Winkler,
• René Gees and
• Bettina Böhlendorf

Beilstein J. Org. Chem. 2013, 9, 2579–2585, doi:10.3762/bjoc.9.293

• intermediate, putatively phloroglucinol (12) [36]. Nitrophenol 13 likely constitutes a direct biosynthetic precursor of the myxocoumarins. Upon O-acetylation of 13 with the long-chain β-keto acid building block 14, putatively recruited from fatty-acid biosynthesis, the intermediate ester 15 could undergo C–C

Approaches to α-amino acids via rearrangement to electron-deficient nitrogen: Beckmann and Hofmann rearrangements of appropriate carboxyl-protected substrates

• Sosale Chandrasekhar and
• V. Mohana Rao

Beilstein J. Org. Chem. 2012, 8, 1393–1399, doi:10.3762/bjoc.8.161

• ] and the Hofmann [10][11][12][13] rearrangements – are not represented in these approaches. This is perhaps surprising, but understandable when the inherent instability of the requisite substrates is considered. Thus, in the Beckmann approach, the oximation of β-keto acid derivatives would be

Asymmetric organocatalytic decarboxylative Mannich reaction using β-keto acids: A new protocol for the synthesis of chiral β-amino ketones

• Chunhui Jiang,
• Fangrui Zhong and
• Yixin Lu

Beilstein J. Org. Chem. 2012, 8, 1279–1283, doi:10.3762/bjoc.8.144

• , catalyzed by cinchonine-derived bifunctional thiourea catalyst has been described. The desired β-amino ketones were obtained in excellent yields and with moderate to good enantioselectivities. Keywords: decarboxylative addition; β-keto acid; Mannich reaction; organocatalysis; Introduction Chiral β-amino

• tosylimine 1a and β-keto acid 2a in the presence of a range of bifunctional catalysts (Table 1). We first evaluated the catalytic effects of several cinchona alkaloid derivatives. Commercially available cinchonidine (CD-1) led to the formation of the product with disappointing enantioselectivity (Table 1

• asymmetric construction of β-amino ketones. Experimental General procedure for the decarboxylative Mannich reaction of β-keto acids and aldimines To a solution of imine 1c (13.8 mg, 0.05 mmol) and C-1 (2.8 mg, 0.005 mmol) in ether (0.5 mL) at room temperature, was added β-keto acid 2a (12.3 mg, 0.075 mmol