Expedient Route Research Articles

Radical-Mediated AnnulationReactions

Radical annulation sequences have proven to be versatile and expedient routes towards highly complex cyclic frameworks. The radical annulation reaction allows for the formation of multiple carbon-carbon bonds in a single operation with regio- and stereocontrol. This review covers annulation reactions that have been carried out by four different pathways.

Fluorinated heterocyclic compounds. An expedient route to 5-perfluoroalkyl-1,2,4-triazoles via an unusual hydrazinolysis of 5-perfluoroalkyl-1,2,4-oxadiazoles: first examples of an ANRORC-like reaction in 1,2,4-oxadiazole derivatives.

The hydrazinolysis reaction of 5-perfluoroalkyl-1,2,4-oxadiazoles has been investigated. Nucleophilic addition of the reagent to the C(5)-N(4) double bond of the oxadiazole ring, followed by ring-opening and then ring-closure involving the beta-nitrogen atom of the hydrazino moiety and the C(3) of the oxadiazole ring, explains the formation of 5-perfluoroalkyl-1,2,4-triazoles as final products. Useful applications in synthesis of this uncommon hydrazinolysis can be claimed.

An Expedient Route to the Tetrazole Analogues of α‐Amino Acids.

AbstractFor Abstract see ChemInform Abstract in Full Text.

An expedient route to the tetrazole analogues of alpha-amino acids.

[reaction: see text] Convenient conditions are described for the transformation of alpha-aminonitriles to the tetrazole analogues of alpha-amino acids. Refluxing the starting material in water/2-propanol at 80 degrees C with sodium azide and catalytic zinc bromide affords the tetrazole product in yields generally exceeding 90%.

ChemInform Abstract: A Facile and Expedient Route to Allyl and Propargyl Amines Using N‐(α‐Benzotriazolylalkyl)amines as Stabilized Iminium Salts.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Tandem N-acyliminium/Pictet–Spengler/intramolecular Diels–Alder reaction: an expedient route to hexacyclic tetrahydro-β-carbolines

A mild and efficient synthesis of rigid hexacyclic nitrogen heterocycles with tetrahydro-β-carboline skeleton is described. Acylation of the imines 7a– d , prepared from tryptamine ( 5 ) and furaldehydes 6a– d , with maleic anhydride at room temperature provided the corresponding hexacyclic nitrogen heterocycles 10a– d via a tandem N-acyliminium/Pictet–Spengler/IMDA reaction. In this tandem approach, five stereocenters, including a quaternary center and three rings are generated with excellent stereoselectivity. Key to the success of this approach is the use of furaldehyde and maleic anhydride as the aldehyde and anhydride components, respectively. Transformation of the free acid to the corresponding amide, ester and alcohol is also studied.

Expedient syntheses of indolizidines (−)-167B and (−)-209D

Indolizidine alkaloids (−)-167B and (−)-209D were synthesized via an expedient route using hydroacylation and amination.

An expedient route to aromatic pyrrolo[2,1- c][1,4]benzodiazepines and a study of their reactivity

2-Hydroxypyrrolo[2,1- c][1,4]benzodiazepines were aromatised in refluxing thionyl chloride into 11-chloropyrrolo[2,1- c][1,4]benzodiazepines in high yield. This aromatic system is doubly reactive towards nucleophiles leading to rearranged products such as iminobenzoxazines and quinazolines.

ChemInform Abstract: An Expedient Route to 2,3‐Substituted and Fused Benzo[a]quinolizine‐4‐thione Framework via Ring Annulation with β‐Oxodithioesters.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

An expedient route to 2,3-substituted and fused benzo[a]quinolizine-4-thione framework via ring annulation with beta-oxodithioesters.

[figure: see text] An efficient highly convergent route to hitherto unreported 2,3-substituted and annulated benzo[a]quinolizine-4-thiones 3 has been developed. The methodology involves ring annulation of 3,4-dihydro-6,7-dimethoxy-1-methylisoquinoline 1 with a variety of readily accessible acyclic and cyclic beta-oxodithioesters 2 in the presence of triethylamine in refluxing benzene. These benzo[a]quinolizine-4-thiones can be readily converted to the corresponding benzo[a]quinolizine-4-ones 5 via dethiomethylative hydrolysis of the respective benzo[a]quinolizinium salts 4 obtained by alkylation of 3 with methyl iodide.

α,β-Unsaturated nitriles: preparative MgO elimination

Double deprotonation of β-hydroxynitriles with MeMgCl (2.1 equiv.) generates a dianion that ejects MgO to provide the corresponding α,β-unsaturated nitriles. Structurally diverse β-hydroxynitriles readily eliminate MgO providing an expedient route to highly substituted α,β-unsaturated nitriles.

An expedient route to the Calabar bean alkaloids (-)-physovenine and (-)-physostigmine.

An expedient route to the Calabar bean alkaloids (-)-physovenine and (-)-physostigmine has been devised using a chiral building block which was originally designed for diastereocontrolled construction of aldohexoses.

Highly diastereoselective dihydroxylation of cis-substituted sulfonyl vinyl oxiranes

An expedient route to rare carbohydrate-like fragments that relies on the highly stereoselective osmium-catalyzed dihydroxylation of 2-sulfonyl-2-hydroxyalkyl-3-vinyloxiranes is outlined.

Lewis acid-directed cyclocondensation of piperidone enol ethers with 2-methoxy-4-(N-phenylsulfonyl)-1,4-benzoquinoneimine: a new regioselective synthesis of oxygenated carbolines

Lewis acid-directed cyclocondensations of piperidone enol ethers with 2-methoxy-4-(N-phenylsulfonyl)-1,4-benzoquinoneimine are reported. Benzofurans are obtained with BF3.OEt2 as a promoter, whereas use of excess amounts of TiCl4:Ti(OiPr)4 leads to tetrahydrocarbolines. The latter reactions provide expedient routes to oxygen-substituted tetrahydrocarbolines and carbolines. As applications of this new methodology, the preparations of 1-[3-(dimethylamino)propyl]amino-7-methoxy- and 1-[3-(dimethylamino)propyl]amino-7,8-dimethoxy-5H-pyrido[4,3-b]indoles are described.

ChemInform Abstract: Stereoselective Reactions of N‐(9‐Phenylfluoren‐9‐yl)‐4‐oxoproline Enolates. An Expedient Route for the Preparation of Conformationally Restricted Amino Acid Analogues.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Stereoselective Reactions of N-(9-Phenylfluoren-9-yl)-4-oxoproline Enolates. An Expedient Route for the Preparation of Conformationally Restricted Amino Acid Analogues

Methodology for the stereoselective preparation of 3-alkylprolines from N-(9-phenylfluoren-9-yl)-4-oxoproline is presented. The enolate of a N-(9-phenylfluoren-9-yl)-4-oxoproline ester was shown to give stereoselective aldol condensations with aromatic and aliphatic aldehydes. The enolate was preferentially approached by the electrophile through the Re face, and high threo selectivity was also observed and provided a route to trans 3-substituted prolines. The reactions are kinetically controlled except for the case of electron-rich or sterically hindered aromatic aldehydes. The ease of the equilibration between the erythro- and threo-aldolates is dictated by the electronic nature of the group at C-4 in substituted benzaldehydes, and the steric compression of the aldehyde group increases the rate of erythro/threo equilibration. Very high stereoselection was also observed in the reductions of the keto group in 3-substituted 4-oxoproline esters. Alkylation or Michael additions of the same enolate were poorly stereoselective, probably due to equilibration of the initially formed products. Kinetic protonation of enolates of 3-alkyl-4-oxoprolines proceeded with high diastereoselection to provide the corresponding cis-3-alkylprolines.

ChemInform Abstract: New Expedient Route to Both Enantiomers of Nonproteinogenic α‐Amino Acid Derivatives from the Unsaturated 2‐Aza‐bicyclo Moiety.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

New Expedient Route to Both Enantiomers of Nonproteinogenic α-Amino Acid Derivatives from the Unsaturated 2-Aza-Bicyclo Moiety

New Expedient Route to Both Enantiomers of Nonproteinogenic a-Amino Acid Derivatives from the Unsaturated 2-Aza-Bicyclo Moiety

ChemInform Abstract: Application of the Evans Aziridination Procedure to 2‐Substituted Acrylates and Cinnamates: An Expedient Route to α‐Substituted α‐ and β‐Amino Acids.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Preparation and Synthetic Utility of 2-Methylselenomethyl Allyl Methyl Selenide. A Valuable Precursor to 2-Silylmethylallyllithiums

3-Lithio-2-[silylmethyl]propenes, easily prepared from 3-methylseleno-2-[silylmethyl]propenes by the cleavage of the C-Se bond, are useful intermediates for the preparation of a variety of functionalised allylsilanes. These allylsilanes are interesting building blocks, used for example, as annelating agents in the efficient synthesis of spiroketals by the Intramolecular Silyl-Modified Sakurai (ISMS) cyclisation. The methodology described in this article provides also an expedient route to a range of heterosubstituted methylselenopropenes, which are valuable precursors to a range of useful heterosubstituted allyllithium reagents. Finally, a one-step preparation of functionalised allylsilanes from readily available 3-methylseleno-2-[methylselenomethyl]propene is reported.