Efficient and fast Heck vinylation of 2-bromo-6-methyl pyridines with methylacrylate. Application to the synthesis of 6-methyl cyclopenta[b]pyridinone

Heck vinylation of 2-bromo-6-methyl-3-substituted pyridines using η³-allylpalladium chloride dimer/P(o-Tol)₃ complex/toluene and dimethylacetamide (DMA) as co-solvent with methyl acrylate is reported. Electronic and steric effects were investigated engaging diversely 2-bromo-3,6-disubstituted pyridines. As application, a new synthesis of the 6-methyl cyclopenta[b]pyridinone building-block connecting Heck vinylation, alkene reduction and Dieckmann condensation is described.     

Stereoselective total synthesis of (−)-zeylenol,a key intermediate for the synthesis of (+)-pipoxide, (−)-uvarigranol G and (−)-tonkinenin A

Total synthesis of (?)-zeylenol, a key intermediate for the synthesis of (+)-pipoxide, (?)-uvarigranol G and (?)-tonkinenin A was achieved from commercially available starting material d-mannose. The key steps are mixed aldol condensation, Grignard reaction, ring closing metathesis and regioselective benzoylation.     

Stereoselective synthesis of N-benzyl conduramine F-1, N-benzyl ent-conduramine E-1, dihydroconduramine F-1 and ent-dihydroconduramine E-1

A short and stereoselective synthesis of conduramine F-1 and ent-conduramine E-1 derivatives have been achieved starting from d-mannitol using nucleophilic vinylation on imine. A concise sequence of vinylation at both ends of d-mannitol and followed by RCM allowed us to prepare target compound.     

Ring-closing metathesis as a new methodology for the synthesis of monomeric flavonoids and neoflavonoids

Basic flavonoid (flavene) and neoflavonoid (neoflavene) skeletons were successfully synthesized using ring-closing metathesis, showing that this methodology can be used as a central synthetic tool for the synthesis of at least two of the three basic flavonoid classes.     

Lewis acid-promoted carbonyl addition of 1,3-bis(silyl)propenes

A novel synthetic protocol for Lewis acid-promoted addition of 1,3-bis(silyl)propenes to N-phenyl glyoxylamide and ethyl glyoxylate is developed. The reaction does not appear to be influenced by the steric bulk of the 1,3-bis(silyl)propenes, and represents a new approach to vinylation of glyoxylates; the products are obtained in good yields.     

Efficient heterogeneous vinylation of aryl halides using potassium vinyltrifluoroborate

An efficient heterogeneously palladium catalysed procedure for the vinylation of aryl iodides and bromides is reported. Using common reaction conditions (Pd/C 2 mol %, AcONa·3H₂O, NMP or NMP/H₂O), good to complete conversions (40-100%) with high selectivities (79-100%) towards the expected vinylaromatic were achieved.     

Dendrimers with 1, 3, 5‐Trisilacyclohexane as Core Unit

1, 1, 3, 3, 5, 5‐Hexavinyl‐1, 3, 5‐trisilacylohexane [Si(CH=CH₂)₂CH₂]₃ was synthesized and hydrosilylated with trichlorosilane to afford the first generation of a dendrimer. Conversion of this molecule with 18 Si–Cl functions on its surface with an excess of vinylmagnesium bromide yielded the 18‐fold vinylated dendrimer. The new compounds were identified by elemental analyses, multi‐nuclear NMR spectroscopy, and mass spectrometry. Crystal structures were obtained for [Si(CH=CH₂)₂CH₂]₃ and [Si(CH₂–CH₂SiCl₃)₂CH₂]₃.     

Intramolecular vinylation of carbanions using N-acyl benzomorpholines as masked vinylureas and vinylcarbamates

Treatment of urea or carbamate derived benzomorpholines with lithium diisopropylamide generates N-vinyl ureas or N-vinyl carbamates by elimination of a phenoxide anion, cleaving the benzomorpholine ring. Simultaneous formation of a carbanion α to a stabilising aryl or nitrile group allows migration of the newly formed N-vinyl substituent to the carbanionic centre, in some cases with high enantiospecificity. Mild hydrolysis of the resulting urea or carbamate returns a C-vinylated amine, alcohol or hydantoin, in some cases with high enantiomeric purity. This ‘masked’ vinylation strategy avoids the need to use the reactive and volatile vinyl isocyanate as a starting material.     

Synthesis of vinylpyrroles, vinylfurans and vinylindoles via a Brønsted acid catalyzed highly regio- and stereoselective cis-hydroarylation of ynamides

A highly regio- and stereoselective Brønsted acid-catalyzed coupling of ynamides and aromatic heterocycles, such as pyrroles, furans, and indoles is described. This process is the equivalent of hydroarylation of ynamides, and leads to the efficient syntheses of an array of vinylheterocycles. Diels-Alder reaction between the vinylindoles and DMAD afforded carbazole derivatives in good yields.     

Preparation of some angularly substituted and highly functionalized quinolizidines as building blocks for the synthesis of various alkaloids and related scaffolds of medicinal interest

The epimeric forms of the angularly substituted quinolizidine 6, representing potentially useful building blocks for the synthesis of various alkaloids, have been prepared via a pathway involving two consecutive ring-closing metathesis reactions. Variously hydroxy-protected derivatives (21, 22, and 26-29) of these compounds have also been generated.