The synthesis of the fusarinic acid, its isomers and homologues

Optically active nitrogen ligands. 1. Synthesis of two optically active monoalkyl-substituted 2-(2-pyridyl)pyridines

“…The signal/noise ratio was then improved by a factor of As applications of the versatile Wittig reaction3,4 are directed toward the synthesis of more complex olefins, the requisite phosphonium salts must frequently incorporate labile functional groups and stereochemically sensitive centers.3a,d The presence of sensitive functionality may limit the use of standard elevated temperature conditions (80-140 °C) for salt formation3,4 and, therefore, provide impetus for developing a new mild method for quaternization of triphenylphosphine. In an SN2 type of displacement reaction which results in ionization, the reaction possesses a negative volume of activation, AV*, and such a reaction should be accelerated under very high pressure (15 kbar, 1.5 GPa). The most typical process of this type is the Menshutkin reaction which involves an amine and an alkyl halide, tne AV* having been reported to lie between -20 and -50 cm3 4mol-1.5…”

“…The observed rate enhancement at elevated pressure, a factor of ten-fold at 2.5 kbar pressure8 ***due in part to a charge development along the reaction course, should also be found in the reaction of triphenylphosphine with primary and secondary halides. The present work shows the great utility of high pressure rate enhancement in the formation of phosphonium salts, permitting reaction to occur between 20 and 40 °C. Ph3P + RX -PH3P+R X-A variety of alkyl bromides and chlorides have beerevaluated in their reaction with triphenylphosphine in different solvents, at different temperatures, and at high (15 kbar, 1.5 GPa) and tow (1 bar) pressure, and the results are summarized in Table I. All reactions at elevated pressure were carried out at either 20 °C or 40 °C for 24 or 36 h. The melting points of the resultant, analytically pure salts were compared with those previously reported.…”

Organic chemistry

“…133 The light-catalysed or induced nucleophilic substitution of p-nitrophenyl phosphate by pyridine, reported last year,134 has been extended to other systems. 135 The nitro-group in p-nitroanisole is displaced by pyridine, 4-methylpyridine, and hydroxide ion.135 With the last reagent ca. 20 % p-nitrophenol is also formed: in the presence of oxygen, other products, including 4-methoxy-2-nitrophen01,13~ have been is01ated.l~~ The first step in these reactions appears to be the absorption of light.…”

“…With rigid systems diaxial opening occurs. Under acidic conditions with dimethyl sulphoxide, and to a greater extent with hexamethylphosphoramide, tram-addition takes place 135. The uses of dimethyl sulphoxide have been reviewed.f36 Ketones can often be deuterated more efficiently by proceeding through the enarnines.l37 A new resolving agent is dehydr~abietylarnine.~~~ A new reagent for electropkilic substitution of aromatic systems is the PhNH ion produced from phenylhydroxylamine in tetrahydrothiophen 1,l -dioxide (sulpholane) with tetrafluoroboric acid.139Friedel-Crafts acylations and related reactions have been reviewed.1405.…”

Concise Total Synthesis and Antifungal Activities of Fusaric Acid, a Natural Product

“…Generally, according to the methods of establishing the target structures, these synthetic approaches can be classified into two categories: by constructing a pyridine ring via Diels-Alder type reactions ( Scheme 1 ) [ 19 , 20 , 21 , 22 ] and by elaborating substituted pyridine intermediates ( Scheme 2 ) [ 23 , 24 , 25 , 26 , 27 , 28 ]. The reported syntheses using Diels–Alder reactions either must be carried out under harsh conditions, or substances such as selenium dioxide (SeO 2 ) [ 21 , 23 , 29 ], gaseous hydrogen chloride (HCl) [ 19 ], potassium permanganate (KMnO 4 ) [ 24 ] and magnesium amalgam [ 24 ], which are both toxic to human body and harmful to the environment, were used, and these methods are not suitable for large-scale synthesis. Substituted pyridine intermediates designed and elaborated can readily facilitate the synthesis of FA and its analogs.…”