A convenient synthesis of pyridazine-3,4-dicarboxylic acid by a hetero diels-alder reaction

A convenient route to prepare unsubstituted pyridazine-3,4-dicarboxylic acid on a preparative scale is described. The synthesis involves a hetero Diels-Alder reaction between a new 1,2-diaza-1,3-diene and ethyl vinyl ether and oxidation of the intermediate 1,4,5,6-tetrahydropyridazine as the key step.     

A convenient and stereoselective synthesis of allylic sulfides

The fractional distillation of 0-(2-alkenyl or 2-cycloalkenyl) S-alkyl dithiocarbonates (xanthates) affords 2-alkenyl or 2-cycloalkenyl alkyl sulfides. The reaction involves the [3,3]-sigmatropic rearrangement of the xanthates to produce S-(2-alkenyl or 2-cycloalkenyl) S-alkyl dithiocarbonates followed by extrusion of carbon oxysulfide to give 2-alkenyl or 2-cycloalkenyl alkyl sulfides.     

A highly stereoselective synthesis of 11Z-retinal using tricarbonyliron complex

A stereoselective synthesis of 11Z-retinal 2, which is the chromophore of visual pigment (rhodopsin), was accomplished from the beta-ionylideneacetaldehyde-tricarbonyliron complex 3. The Peterson reaction of 3 using ethyl trimethylsilylacetate smoothly proceeded to afford predominantly the Z-ester 6. Transformation of the Z-ester 6 to the methyl ketone 19, followed by the Emmons-Horner reaction of 19 with C2-cyanophosphonate, produced ethyl 11Z, 13E-retinonitrile-tricarbonyliron complex 21 as the only product. Decomplexation of 21 with CuCl2 and subsequent DIBAL reduction gave 11Z-retinal 2 in excellent yield. Mechanistic consideration of Z-selectivity in the Peterson reaction of the aldehyde-tricarbonyliron complex is also discussed.     

A convenient synthesis of 3-aryl-3,4-dihydroisoquinolinium salts

A convenient synthesis of the title compounds proceeding via direct Bischler-Napieralski cyclization reaction of the appropriate N,N-dialkylformamides obtained from the adequate imines is described. The reported procedure implies synthetically useful yields and mild reaction conditions.     

A highly stereoselective synthesis of Z-1,2-dialkylvinylsilanes from acylsilane/ylide chemistry

The reaction, in the presence of soluble lithium salts, of non-stabilized ylides at low temperature with aliphatic derivatives of acylsilanes gives moderate to good (37–82%) yields of Z-1,2-disubstituted vinylsilanes in excellent (96%) isomeric purities for normal alkyl derivatives. Implications of these results on the mechanistic aspects of the Wittig olefination are discussed     

A convenient synthesis of immunosuppressive agent FTY720 using the petasis reaction

A convenient synthesis of immunosuppressive agent FTY720 (1) using the Petasis reaction was developed. 4-Octylbenzaldehyde (9) was converted into 1-ethenyl-4-octylbenzene (11) by two-step synthesis. Hydroboration of 11 using catecholborane and hydrolysis gave (E)-2-(4-octylphenyl)vinylboronic acid (4). The Petasis reaction of 4, dihydroxyacetone (3), and benzylamine following catalytic hydrogenation afforded FTY720 (1).     

A convenient synthesis of 3,4-dihydro-1,4-benzoxazin-2-ones

3,4-Dihydro-1,4-benzoxazin-2-one was prepared for the first time by catalytic hydrogenation of 4-benzyl-3,4-dihydro-1,4-benzoxazin-2-one. A simple and efficient synthesis of 4-benzyl- and 4-alkyl-3,4-dihydro-1,4-benzoxazin-2-one derivatives from ethyl 2-(2-hydroxyphenylamino)acetate and aldehydes is described. Some considerations regarding the reactivity of 3,4-dihydro-1,4-benzoxazin-2-ones are given.     

A convenient synthesis of olefins via deacylation reaction

A convenient and environmentally-friendly synthetic method of olefins via deacylation reaction is described. The reaction gives olefins by condensation of aldehydes with a variety of 1,3-dicarbonyl compounds in the presence of anhydrous potassium carbonate at room temperature in high yields (70-90%) in one step. The synthetic potential of this strategy can be used as an alternative procedure to the Wittig, Wittig-Horner reactions. The stereochemistry of the resulted olefins was determined by NOE experiment with correct radio frequency and X-ray analysis. The E/Z selectivity of the deacylation reaction depends on the α-substituents of the 1,3-dicarbonyl compounds.     

A convenient and highly stereoselective synthesis of 14-substituted 8,13-diazaoestrone analogues by domino ring closures

By means of convenient domino ring closure reactions of 1-(2-aminoethyl)-6,7-dimethoxy-1,2,3,4-tetrahydroisoquinoline 2 and γ-oxo-acids, 14-substituted 8,13-diazaoestrone derivatives (5 and 6) were formed with ∼100% diastereoselectivity.     

A convenient synthesis of muscimol by a 1,3-dipolar cycloaddition reaction

A simple and large scale approach to the synthesis of muscimol 7 has been developed starting from the easily available dibromoformaldoxime 1.     

First total synthesis of salinipyrone A using highly stereoselective vinylogous Mukaiyama aldol reaction

A synthetic approach for the total synthesis of salinipyrone A has been developed. Key steps involve the TiCl₄-mediated vinylogous Mukaiyama aldol reaction (VMAR) of chiral ketene silyl N,O-acetal with propionaldyhyde, an aldol condensation, Witting olefination, and a cyclization. The synthesis proceeds in eight steps.     

A convenient synthesis of novel pyridazino[3,4-b]quinoxaline and pyrazolo[3,4-b]quinoxaline utilizing 1,3-dipolar cycloaddition reaction

The reaction of 2,6-dichloroquinoxaline 4-oxide 4 with methylhydrazine gave 6-chloro-2-(1-methylhydrazino)quinoxaline 4-oxide 5, whose reaction with dimethyl acetylenedicarboxylate or 2-chloroacrylonitrile resulted in the 1,3-dipolar cycloaddition reaction to afford 7-chloro-3,4-bismethoxycarbonyl-1-methyl-1,2-dihydropyridazino[3,4-b]quinoxaline 6 or 6-chloro-3-hydroxymethylene-1-methyl-2,3-dihydro-1H-pyrazolo[3,4-b] quinoxaline hydrochloride 7, respectively.     

A convenient synthesis of novel pyridazino[3,4-b]quinoxalines

Novel 4-chlorophenylhydrazono-3-oxo-1,2,3,4-tetrahydropyridazino[3,4-b]quinoxalines 10a-c were synthesized by the cyclization of the α-hydrazonohydrazides 8a-c. The chlorination of 10a with phosphoryl chloride afforded 3-chloro-4-[2-(o-chlorophenyl)hydrazino]pyridazino[3,4-b]quinoxaline 12.     

A convenient stereoselective synthesis of 5-hydroxy-3-oxoesters and 3-hydroxy-5-oxoesters

A biocatalytic approach was employed for the asymmetric reduction of sterically demanding ketones to prepare 3-hydroxy-5-oxo-5-phenylpentanoates and 5-hydroxy-3-oxo-5-phenylpentanoates. Screening a collection of microorganisms led to the identification of stereocomplementary microbial strains that provide access to both enantiomers of 3-hydroxy-5-oxo-5-phenylpentanoates and 5-hydroxy-3-oxo-5-phenylpentanoates with high enantiomeric excess (up to 99% ee). Moreover, the application of Saccharomyces cerevisiae gave two diastereomers of 3,5-dihydroxy-5-phenylpentanoates with high enantiomeric excess (up to 99% ee). The applicability of the identified strains was demonstrated by transforming the obtained dihydroxy ester into the chemically valuable lactone (4S,6R)-tetrahydro-4-hydroxy-6-phenyl-pyran-2-one.     

A short and convenient procedure for the stereoselective synthesis of 2-hydroxy-1-norbornanesulfonamides

A short and convenient procedure for the stereoselective synthesis of novel optically active 2-hydroxy-1-norbornanesulfonamides starting from commercially available natural camphor and fenchone is reported. The synthetic route involves a nucleophilic substitution at the sulfenyl sulfur atom of 2-methylene-1-norbornylthiotriflates followed by oxidation of the intermediate sulfenamides and highly diastereoselective reduction of the carbonyl group of the parent 2-oxo-1-norbornanesulfonamides.     

A convenient stereoselective synthesis of a (−)-vertinolide precursor

A short practical method for the enantioselective synthesis of (−)-vertinolide precursor 2 is described. The readily available chiral β-alkoxy substituted acrylate 7 has been reacted with the ethyl levulinate to form the tetronic acid nucleus 8, which in three subsequent steps was converted to the known precursor 2 in high overall yield.     

Total synthesis of khafrefungin using highly stereoselective vinylogous Mukaiyama aldol reaction

[structure: see text] A convergent total synthesis of khafrefungin was accomplished on the basis of (1) the highly stereoselective TiCl4-mediated vinylogous Mukaiyama aldol reaction using vinylketene silyl N,O-acetal and (2) syn-selective aldol reaction of enal 5a and ethyl ketone 6 followed by anti-dehydration under Mitsunobu conditions.     

A convenient stereoselective synthesis of trifluoromethyl-substituted polyfunctionalized cyclopropane: synthesis of (+/-)-trans-trifluoronorcoronamic acid

Trifluoromethylated polyfunctionalized cyclopropanes were obtained in high stereoselectivity by reacting 2-bromo-3,3,3-trifluoropropene (BrTFP) with active methylenes. This novel method was further applied to the synthesis of (+/-)-trans-trifluoronorcoronamic acid.