- Synthesis and pyrolysis of two novel pyrrole ester flavor precursors
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In order to develop the high-temperature-released pyrrole aroma, two novel flavors precursors of methyl 2-methyl-5-(((2-methylbutanoyl)oxy)methyl)-1-propyl-1H-pyrrole-3-carboxylate and methyl 2-methyl-5-(((2-methylbutanoyl)oxy)methyl)-1-propyl-1H-pyrrole-3-carboxylate were synthesized using glucosamine hydrochloride and methyl acetoacetate as raw materials through cyclization, oxidation, alkylation, reduction, and esterification. The target compounds were characterized by nuclear magnetic resonance (1H NMR, 13C NMR), infrared spectroscopy (IR) and high-resolution mass spectrometry (HRMS). Thermogravimetry (TG), differential scanning calorimeter (DSC) and the pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS) methods were used to analyze the heating-stability of the target compounds, and the pyrolysis mechanism was inferred. Py-GC/MS results indicated that some fragrance compounds were formed during?thermal degradation such as 2-methylbutyric acid, 2-methylbutyrate, alkylpyrroles, and benzoic acid, which were important aroma components or flavor additives. This provided a theoretical reference for the application of pyrrole ester in cigarette and heat-processed food flavoring.
- Cheng, Biao,Chu, Wenjuan,Fan, Wenpeng,Feng, Yingjie,Gao, Ziting,Ji, Xiaoming,Lai, Miao,Tian, Haiying,Zhang, Zhan
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- Regioselective synthesis of 2,3,4- or 2,3,5-trisubstituted pyrroles via [3,3] or [1,3] rearrangements of O-vinyl oximes
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The regioselective synthesis of 2,3,4- or 2,3,5-trisubstituted pyrroles has been achieved via [3,3] and [1,3] sigmatropic rearrangements of O-vinyl oximes, respectively. Iridium-catalyzed isomerization of easily prepared O-allyl oximes enables rapid access to O-vinyl oximes. The regioselectivity of pyrrole formation can be controlled by either the identity of the α-substituent or through the addition of an amine base. When enolization is favored, a [3,3] rearrangement followed by a Paal-Knorr cyclization provides a 2,3,4-trisubstituted pyrrole; when enolization is disfavored, a [1,3] rearrangement occurs prior to enolization to produce a 2,3,5-trisubstituted pyrrole after cyclization. Optimization and scope of the O-allyl oxime isomerization and subsequent pyrrole formation are discussed and mechanistic pathways are proposed. Conditions are provided for selecting either the [3,3] rearrangement or the [1,3] rearrangement product with β-ester O-allyl oxime substrates.
- Wang, Heng-Yen,Mueller, Daniel S.,Sachwani, Rachna M.,Kapadia, Rachel,Londino, Hannah N.,Anderson, Laura L.
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supporting information; experimental part
p. 3203 - 3221
(2011/06/24)
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- Catalytic asymmetric hydrogenation of 2,3,5-trisubstituted pyrroles
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Catalytic asymmetric hydrogenation of N-Boc-protected pyrroles proceeded with high enantioselectivity by using a ruthenium catalyst modified with a trans-chelating chiral bisphosphine PhTRAP. The ruthenium catalyst prepared from Ru(η3-methallyl
- Kuwano, Ryoichi,Kashiwabara, Manabu,Ohsumi, Masato,Kusano, Hiroki
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p. 808 - 809
(2008/09/20)
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- Facile and efficient synthesis of pyrroles and indoles via palladium-catalyzed oxidation of hydroxy-enamines and -amines
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The palladium-catalyzed oxidation of hydroxy-enamines, which were obtained by the condensation of β-aminoalcohols and carbonyl compounds, proceeded to give the corresponding polysubstituted pyrroles and 4,5,6,7-tetrahydroindoles in good yields. The treatment of o-(2-hydroxyethyl)aniline with the palladium catalyst also gave indole in 78% yield.
- Aoyagi, Yutaka,Mizusaki, Toshihiko,Ohta, Akihiro
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p. 9203 - 9206
(2007/10/03)
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