Wyniki wyszukiwania - Biblioteka Nauki

1

Synteza polihydroksyindolizydyn z L,B-nienasyconych [delta]-laktonów

100%

Rabiczko J. , Socha D. , Jurczak M. , Chmielewski M.

Wiadomości Chemiczne

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2002

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tom [Z] 56, 7-8

561-583

EN

The isolation, synthesis and biological properties of polyhydroxylated alkaloids (iminosugars) constitute a well-visible trend in organic chemistry nowadays. Due to their structural resemblance to sugars, iminosugars are recognized by glycosidases, the enzymes that catalyse the hydrolysis of glycosidic bonds in carbohydrates and glycoconjugates. Since glycosidases play a very important role in many biological systems, the iminosugars which inhibit them display interesting biological activities. Indolizidines represented by castanospermine, swainsonine and lentiginosine are particularly interesting as they exhibit a variety of important biomedical properties. The present paper is not a survey of the literature, but only deals with syntheses towards lentiginosine, with the aim of illustrating representative approaches in the syntheses of polyhydroxyindolizidines. The high stereoselectivity of both the conjugate addition of hydrazine and the (1,3)-dipolar cycloaddition of nitrones to the a,b-unsaturated sugar d-lactones, prompted us to use the adducts of both reactions as substrates for the syntheses of polihydroxyindolizidines. The conjugate addition offers a stereocontrolled entry to derivaties of both D- and L-2-pyrrolidineacetic acids which can be easily transformed into desired indolizidines. As an example, the syntheses of lentiginosine are demonstrated. The (1,3)-dipolar cycloaddition of Brandi's nitrone to the title lactones proceeded with high stereoselectivity in the case of D- and L-glycero lactones, whereas there was a high kinetic resolution in the case of racemic D,L-glycero lactone. It was shown that adducts can be easily transformed into lentiginosine, 7-hydroxylentiginosine and 7,8-dihydroxylentiginosine.

2

Otrzymywanie hydrofobowych półproduktów do syntezy diesterquatów z wykorzystaniem wielofunkcyjnego reaktora LabMax

84%

Zieliński W. , Skrzela R. , Lamch Ł. , Wilk K. A.

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tom T. 91, nr 4

499-505

PL

Przedstawiono wyniki badań wpływu parametrów, takich jak temperatura i szybkość dozowania substratu, na przebieg reakcji addycji Michaela w wielkolaboratoryjnych badaniach procesu addycji metyloaminy do akrylanów alkilowych. Dokonano optymalizacji warunków reakcji Michaela decydującej o kinetyce procesu. Zastosowanie odpowiedniej temperatury początkowej i szybkości dozowania roztworu metyloaminy pozwoliło na zwiększenie wydajności procesu (w stosunku do wcześniej stosowanych warunków) i praktyczne wyeliminowanie tworzenia się produktów ubocznych.

EN

Three CH₂=CHCOOR (R = Me, C₆H₁₃, C₁₂H₂₅) were converted with MeNH₂ at 10–20°C in alc. soln. (2 L reactor) to resp. MeN(CH₂CH₂COOR)₂ diesterquats. The reaction course was followed by IR spectroscopy to det. the optimum rate of MeNH₂ dosing. The reaction yield decreased with increasing the dosing rate and the R chain length. The initial temp. did not show any substantial effect on the reaction course.

3

Zastosowanie trietyloaminy w syntezie organicznej

67%

Kowalski P. , Sikorska-Jarosz J.

Wiadomości Chemiczne

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2003

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tom [Z] 57, 11-12

1133--1162

EN

This review shows examples of application of Et3N in oxidations, eliminations, substitutions, and addition reactions. Triethylamine (Et3N) appears to be most popular organic amine base in organic synthetic chemistry. The popularity comes from its low price along with easiness of removal by distillation. However, Et3N is a very dangerous fire hazard when exposed to the heat, flame, or oxidizers. Their salts with inorganic acids are somewhat insoluble in most organic solvents of low polarity and for that reason may by removed from the reaction media by simple filtration. Examples of application of Et3N in oxidation reactions are shown in ozonolysis of cycloalkene 1-8 [3-5] (figs 1-4-5), and figs 1-6-8 show oxidation of 1-14, 1-16, and 1-18 alcohols, employing activated DMSO [6-12]. Various oxidation processes of hydrazones with iodide in the presence of Et3N are presented in fig. 1-9 [13]. Elimination reactions, concerned mainly with dehydrohalogenations, are described in examples of halogen derivatives of lactone 2-1 [17], ketone 2-3 [18,19], sulfone 2-6 [20], and acids 2-9 and 2-11 [21,22] (figs 2-1-5). Dehalogenation of 2-13 [23], 2-17 [26-28], and 2-22 [31-37] acid chlorides are presented in figs 2-6-8, while formation of nitrile oxides in figs 2-11-13 [38-42]. Competitive dehydrobromination and dehydrochlorination reaction occurs in the presence of Et3N in 1,1,1-trichloro-3-bromo-3-fenylopropane (2-35) is described in fig. 2-15 [44]. Mechanizm and examples of transformation of chlorosulfonyl chlorides are presented in figs 2-17-20 [47-51], and dimerization of aldiminium salts [63] in fig. 2-25 as well. Applications of Et3N in carbon-carbon bond formation in an intramolecular Heck reaction are shown in fig. 3-1 [70-74]. Example of use of Et3N in enolboronation of carbonyl compounds is described in fig. 3-2 [75-78], and additionally, in synthesis of silyl enol ethers can be found in figs 3-3-6 [89-104]. Application of Et3N as the base in neutralizing the acids liberated in preparing diazo ketones and mixed anhydrides are indicated in fig. 3-7 [105-107] and fig. 3-8 [108-117] respectively, while in protecting of hydroxy group in figs 3-9-11 [118-126]. Use of Et3N as the effective catalyst in cyjanoethylation reaction of active methyl group in acetylacetone (4-2) [130] and alkylpyridine methiodides 4-4-5, 4-8-9 [131] are shown in figs 4-1-3, and in isomerization reaction of pyrazolines 4-14 [133] and cycloaddition of indane-1,3-dione (4-16) [134] in figs.4-5?6.