A synthesis of hydrothiopyran-3-ones. The intramolecular cyclization of allylthiopropionyl and propargylthioacetyl chlorides

Intramolecular cyclization of 2-(allylthio)propionyl chloride ( 3a ) effected by aluminum chloride gave two dihydrothiopyran-3-ones ( 5a,6a ) and 5-chloro-2-methyltetrahydrothiopyran-3-one ( 7a ). Treatment of propargylthioacetyl chloride ( 4a ) with aluminum chloride afforded 5-chloro-3,6-dihydro-2H-thiopyran-3-one ( 10a ). The cyclization reactions of related compounds were also studied.     

Gold-catalyzed intramolecular cyclization of alkynones with pyridine anhydrobases

4-Alkylpyridines functionalized with alkynyl amide substituents can be converted to pyridyl-substituted lactams via Au-catalyzed cyclization at the pyridine benzylic carbon. These transformations proceed through alkylidene dihydropyridine (anhydrobase) intermediates and demonstrate the ability to utilize these species in metal-catalyzed C–C bond forming reactions.     

High-yielding intramolecular direct arylation reactions with aryl chlorides

[reaction: see text] An N-heterocyclic carbene palladium catalyst system is used to promote direct arylation of a broad range of aryl chlorides to form six- and five-membered ring biaryls. An influence of the halide on the palladium precatalyst on catalyst activation has been revealed, as has a beneficial effect of NHC salts that allows the turnover numbers to be increased by simple addition of imidazolium salts to the reaction mixture.     

Intramolecular cyclization of cycloalkene carboxylic acid chlorides

Thermal cyclization of cyclooctene-4-yl-carboxylic acid chloride (5) and cycloheptene-4-yl-carboxylic acid chloride (10) yielded mixtures of mainly endo and exo 2-chlorobicyclo[3.3.1]nonane-9-one (7 and 8), and mixtures of endo and exo 2-chlorobicyclo[3.2.1]octane-8-one (12 and 13), respectively. AlCl₃-catalyzed cyclization of 10 gave the same product composition as the uncatalyzed reaction. In the AlCl₃-catalyzed cyclization of 5 considerable amounts of bicyclo[3.3.1]non-2-en-9-one (6) and exo 3-chlorobicyclo[3.3.1]nonane-9-one (9) were obtained in addition to 7 and 8.     

Ruthenium-catalyzed intramolecular cyclization of hetero-functionalized allylbenzenes

Intramolecular addition of heterofunctionalities to CC double bonds without β-hydride elimination was investigated and catalyzed by ruthenium complexes. The combination of RuCl₃ · nH₂O (10 mol%) and 3 equiv. of AgOTf acted as a catalyst for cyclization of 2-allylphenol (1a) to 2,3-dihydro-2-methylbenzofuran (2a) in good yield in the presence of Cu(OTf)₂ as a co-catalyst and PPh₃ as a ligand. This catalyst system also catalyzed the cyclization of 2-allylbenzoic acid to lactone in 91% yield. Then, a new catalyst system (RuCp¹Cl₂)₂ (1.0 mol%)/4AgOTf/4PPh₃, was found to be more active even in the absence of Cu(OTf)₂. Furthermore, this catalysis was applied to asymmetric reaction of 2-allylphenol (1a). When using TolBINAP as a ligand, over 60% e.e. was achieved.     

Efficient nickel-mediated intramolecular amination of aryl chlorides

The use of an in situ generated Ni(0) catalyst associated with 2,2'-bipyridine or N,N'-bis(2,6-diisopropylphenyl)dihydroimidazol-2-ylidene (SIPr) as a ligand and NaO-t-Bu as the base for the intramolecular coupling of aryl chlorides with amines is described. The procedure has been applied to the formation of five-, six-, and seven-membered rings. [reaction: see text]     

Indium trichloride mediated intramolecular Prins-type cyclization

[reaction: see text] Intramolecular Prins-type reactions of compounds having both functionalities of homoallyl alcohol and acetal moiety are described. The intramolecular Prins cyclizations were performed using indium trichloride in chloroform or 25% aqueous THF. Both 9-oxabicyclo[3.3.1]nonane and 3,9-dioxabicyclo[3.3.1]nonane compounds were successfully obtained in moderate yields.     

A reversible pH-dependent intramolecular pyridine-aldehyde cyclization

A dipicolylamine (DPA) attached to an aldehyde moiety cyclizes to form a pyridinium-fused heterocycle. This intramolecular reaction between the pyridine and aldehyde moieties is reversible, and the position of the equilibrium is controlled by pH. The fused-ring heterocycle is stabilized under acidic conditions, whereas the ring-opened form is the major species under basic conditions. The ring-closed form can be utilized as a masked aldehyde precursor to access a variety of functional metal chelators containing the DPA unit.     

Consecutive cyclization of allylaminoalkene by intramolecular aminolithiation-carbolithiation

Consecutive cyclization of allylaminoalkenes by tandem aminolithiation-carbolithiation proceeded smoothly by using a lithium amide as a lithiating agent as well as protonating agent to give bicyclic amines, octahydroindolizine and hexahydro-1 H-pyrrolizine, in reasonably high yield and diastereoselectivity.     

Synthesis and intramolecular cyclization of bisthiadiazinylmethane derivatives

Bisthiadiazinylmethane derivatives obtained from 1,2,6-thiadiazine 1,1-dioxides and formaldehyde, undergo unusual intramolecular cyclizations to thiadiazino [4,3-g] [2,1,3] benzothiadiazine tetraoxides. The structures of the newly synthesized compounds are discussed on the basis of ¹H and ¹³C-NMR data and X-ray analysis.     

Uncommon intramolecular palladium-catalyzed cyclization of indole derivatives

A novel synthetic strategy based on the intramolecular palladium-catalyzed oxidative cyclization reaction, allows the formation of C-C bond and the synthesis of β-carbolinones. The reaction has been performed in the presence of catalytic amount of PdCl₂(CH₃CN)₂ and benzoquinone as a reoxidant.     

The intramolecular reductive cyclization of cyclic enones

The reductive cyclization (electrohydrocyclization reaction) of tethered cyclic enones has been investigated under electrochemical, metal-mediated, and photochemical conditions. The tricyclic products are generally formed with excellent stereoselectivity, particularly if at least one of the enones is β,β-disubstituted.     

Reaction of isopropenylcyclopropane with arylsulfenyl chlorides and the isomerization of the adducts

Conclusions The addition of arylsulfenyl chlorides to isopropenylcyclopropane may, according to the polarity of the medium, proceed by normal addition at the double bond to give the 1,2-adducts, or by homoallyl rearrangement to give the corresponding homoprenyl chlorosulfides. Some bifunctional isoprenoid C₆-synthones have been obtained.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 10, pp. 2314–2319, October, 1984.     

A novel intramolecular Diels-Alder cyclization involving indoloazepines

The reaction of indoloazepines 1 and α,β-unsaturated aldehydes in reflux toluene led to tetracyclic compounds 2. The key to this reaction was an intramolecular Diels-Alder cycloaddition by the indoloacrylate (dienophile)-dienamine (diene) intermediates generated in situ.     

Unusual cyclization of trimethylsilyl derivative of trisacetylhydrazine

Conclusions The trimethylsilylation of trisacetylhydrazine is accompanied by rearrangement to 2,5-dimethyl-4-acetyl-5-trimethylsiloxy-1, 3,4-oxadiazoline-2.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 3, pp. 694–695, March, 1984.     

Synthesis of riccardin B by nickel-catalyzed intramolecular cyclization

Riccardin B, a macrocyclic bis(bibenzyl) possessing cytotoxic activity, and its dehydroxy derivative were synthesized in high yields using the nickel-catalyzed intramolecular coupling of the acyclic precursors.     

Unusual synthesis of dihydropyrido[2,1-a]isoindolone derivatives by radical cyclization of enamides of Baylis-Hillman adducts

During the radical cyclization of enamide derivatives 4 we found unusual formation of dihydropyrido[2,1-a]isoindolone derivatives 5. The enamides were synthesized in four steps from the Baylis-Hillman adducts of ortho-bromobenzaldehydes.