Iron(III)-catalyzed Prins-type cyclization using homopropargylic alcohol: a method for the synthesis of 2-alkyl-4-halo-5,6-dihydro-2H-pyrans

[reaction: see text] A new Prins-type cyclization between homopropargylic alcohol and aldehydes in the presence of FeX(3) to obtain 2-alkyl-4-halo-5,6-dihydro-2H-pyrans in good yield is described. Osmium-catalyzed cis dihydroxylation provided direct access to trans-2-alkyl-3-hydroxy-tetrahydro-pyran-4-ones. Anhydrous ferric halides are also shown to be excellent catalysts for the standard Prins cyclization using homoallylic alcohol. Isolation of an intermediate acetal provides substantiation of a proposed mechanism.     

Iron(III)-catalyzed Conia-ene cyclization of 2-alkynic 1,3-dicarbonyl compounds

A cheap, simple, and effective FeCl(3)-catalyzed Conia-ene cyclization of 2-alkynic 1,3-dicarbonyl compounds was stereospecific to afford alkylidenecyclopentanes in (E)-isomers via the 5-exo-dig pathway. The 5-endo-dig and 6-exo-dig cyclizations were also possible, depending on the structure of the substrates.     

Palladium(II)-catalyzed cyclization of urethanes and total synthesis of 1-deoxymannojirimycin

The palladium(II)-catalyzed cyclization of the urethane 8, which was derived from D-mannitol, gave the cyclic compound 9 with excellent diastereoselectivity. During these transformations, the Pd(II) species are not reduced and thus the catalyst can recycle without its reoxidation. The cycloadduct 9 was converted to 1-deoxymannojirimycin.     

Platinum(II)-catalyzed intramolecular cyclization of alkynylbenzonitriles: synthesis of 1-alkoxyisoquinolines and isoquinolones

A facile synthesis of a series of 1-alkoxyisoquinolines and (2H)-isoquinolones by an intramolecular 6-endo-dig cyclization of ortho-alkynylbenzonitriles in the presence of a catalytic amount of hydrido(dimethylphosphinous acid-κP)[hydrogen bis(dimethylphosphinito-κP)]platinum(II) in various alcohols at 65-90 °C is described for the first time.     

Indium(III)-catalyzed hydrative cyclization of 1,7-diynyl ethers

A new hydrative cyclization of 1,7- and 1,8-diynyl ethers is reported. Using catalytic InI(3) and p-TSA as a cocatalyst, several 2,2-disubstituted tetrahydrofurans with exocyclic enone appendages were prepared. Reaction optimization and scope, mechanistic insight, and further transformation to a C-nucleoside analog are presented.     

Ti(III)-catalyzed radical cyclization of 6,7-epoxygeranyl acetate

The reductive cyclization of epoxygeranyl acetate (1) was investigated using a catalytic amount of Cp₂TiCl with various additives. The newly developed Cp₂TiCl-Mn-lutidine · HCl-BEt₃ system was found to be as effective as the reported stoichiometric system to afford the cyclized dehydro products 4 and 5 with 72% selectivity.     

Palladium(0)-catalyzed stereoselective cyclization of allenenes: divergent synthesis of pyrrolidines and 3-azabicyclo[3.1.0]hexanes from single allenenes

Two novel palladium(0)-catalyzed cyclizations of allenenes are described. Treatment of allenenes such as N-(1-alkyl-2,3-butadienyl)-N-allylsulfonamide with an aryl halide and K(2)CO(3) in the presence of a catalytic amount of Pd(PPh(3))(4) in dioxane affords 2,3-cis-pyrrolidines in a stereoselective manner. In sharp contrast, cyclization of the same allenenes using catalytic Pd(2)(dba)(3) x CHCl(3) in the presence of allyl methyl carbonate in CH(3)CN leads to stereoselective formation of a 3-azabicyclo[3.1.0]hexane framework in moderate yields.     

Phosphoramidite gold(I)-catalyzed diastereo- and enantioselective synthesis of 3,4-substituted pyrrolidines

In this article the utility of phosphoramidite ligands in enantioselective Au(I) catalysis was explored in the development of highly diastereo- and enantioselective Au(I)-catalyzed cycloadditions of allenenes. A Au(I)-catalyzed synthesis of 3,4-disubstituted pyrrolidines and γ-lactams is described. This reaction proceeds through the enantioselective Au(I)-catalyzed cyclization of allenenes to form a carbocationic intermediate that is trapped by an exogenous nucleophile, resulting in the highly diastereoselective construction of three contiguous stereogenic centers. A computational study (DFT) was also performed to gain some insight into the underlying mechanisms of these cycloadditions. The utility of this new methodology was demonstrated through the formal synthesis of (-)-isocynometrine.     

Asymmetric synthesis of trans-2,5-disubstituted pyrrolidines from enantiopure homoallylic amines. Synthesis of pyrrolidine (-)-197B

Iodocyclization of sulfinimine-derived enantiopure homoallylic sulfonamides affords trans-2,5-disubstituted 3-iodopyrrolidines and represents valuable methodology for the asymmetric synthesis of this important heterocyclic ring system.     

Nickel(0)-catalyzed cyclization of N-benzoylaminals for isoindolinone synthesis

A nickel(0) catalyst effectively mediates the cyclization of N-benzoyl aminals in the presence of a stoichiometric Lewis acid. This method enables preparation of a variety of isoindolinones with substitution on the benzoyl fragment and C-3 carbon. This reaction likely proceeds via an α-amidoalkylnickel(II) intermediate, which then may cyclize via either an electrophilic aromatic substitution or an insertion pathway.     

Asymmetric synthesis of cis- and trans-2,5-disubstituted pyrrolidines from 3-oxo pyrrolidine 2-phosphonates: synthesis of (+)-preussin and analogs

Pyrrolidine enones, derived from 3-oxo pyrrolidine 2-phosphonates and a HWE reaction with aldehydes, on Luche reduction give pyrrolidine allylic alcohols. The alcohols on hydrogenation (Pd/H2) give cis-2,5-disubstituted pyrrolidines and on treatment with TFA-NaBH3CN undergo a hydroxy directed reduction to trans-2,5-disubstituted pyrrolidines.     

One-pot copper(I)-catalyzed synthesis of 3,5-disubstituted isoxazoles

[reaction: see text] 3,5-Disubstituted isoxazoles are obtained in good yields by a convenient one-pot, three-step procedure utilizing a regioselective copper(I)-catalyzed cycloaddition reaction between in situ generated nitrile oxides and terminal acetylenes. Most functional groups do not interfere with the reaction, which can be performed in aqueous solvents without protection from oxygen. Since all reagents are used in stoichiometric amounts, formation of byproducts is minimized.     

Efficient synthesis of enantiomerically pure trans-2,5-bis(arylethynyl)pyrrolidines. A new entry into C2-symmetric chiral secondary amines

A new class of C₂-symmetric pyrrolidine derivatives bearing arylethynyl groups at the 2,5-positions has been synthesized in enantiomerically pure form from 1,7-octadiyne-3,6-diol in five steps. Some notable features of the synthesis are: (i) the formation of a separable diastereomeric mixture of pyrrolidine carbamates using a newly prepared chiral chloroformate; and (ii) the development of a new method for the deprotection of the carbamate via a novel SmI₂-promoted electron transfer process.     

Tandem Rh(III)-catalyzed oxidative acylation of secondary benzamides with aldehydes and intramolecular cyclization: the direct synthesis of 3-hydroxyisoindolin-1-ones

The rhodium-catalyzed oxidative acylation between secondary benzamides and aryl aldehydes via sp(2) C-H bond activation followed by an intramolecular cyclization is described. This method results in the direct and efficient synthesis of 3-hydroxyisoindolin-1-one building blocks.     

Gold(III) chloride catalyzed cyclization of alpha-hydroxyallenes to 2,5-dihydrofurans

[reaction: see text] Functionalized alpha-hydroxyallenes 1 were smoothly converted into the corresponding 2,5-dihydrofurans 2 by using 5-10 mol % of gold(III) chloride as catalyst. This mild and efficient cyclization method can be applied to alkyl- and alkenyl-substituted allenes at room temperature, furnishing tri- and tetrasubstituted dihydrofurans in good to excellent chemical yields and with complete axis to center chirality transfer.     

Ru(III)-catalyzed cyclization of arene-alkene substrates via intramolecular electrophilic hydroarylation

[reaction: see text] We herein report that RuCl(3)/AgOTf has proven to be a hydroarylation catalyst with an efficiency and scope superior to previously known methods. This catalyst demonstrated consistent performance with arene-ene substrates of diverse structural features, providing good to excellent yields of cyclization products (chromanes, tetralins, terpenoids, dihydrocoumarins).     

Investigation of 2,6-dichlorojulolidines and 1-aryl-2,5-di(chloromethyl)pyrrolidines

9-Substituted 2,6-dichlorojulolidines and 1-aryl-2,5-di(chloromethyl)pyrrolidines-alkylating compounds with alkylating centers in fixed positions — were synthesized, and their basicities and rates of hydrolysis were determined. The relationship between the structure, basicity, and rate of hydrolysis of these compounds is discussed.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 1, pp. 41–44, January, 1972.     

Synthesis of substituted bis(3,3-dialkyl-3,4-dihydro-1-isoquinolyl)methanes

Symmetrical and non-symmetrical substituted bis(3,4-dihydro-1-isoquinolyl)methanes were synthesized by fusion of substituted 1-methylthio-3,4-dihydroisoquinolines with 1-methyl-3,4-dihydroisoquinolines and by the Ritter reaction of 1,1-dialkyl-2-arylethanols with 1-cyanomethylidene-1,2,3,4-tetrahydroisoquinoline or malononitrile.