Facile syntheses of substituted 2,3-dihydrofurans and benzofurans by palladium-catalyzed reactions of propargylic carbonates with nucleophiles

Substituted 2,3-dihydrofurans and benzofurans are synthesized by the palladium-catalyzed reaction of 5-methoxycarbonyloxy-3-pentyn-1-ols and 1-(2-hydroxyphenyl)-3-methoxycarbonyloxy-1-propyne with nucleophiles, respectively. Various substituted propargylic carbonates and nucleophiles are efficiently transformed to their corresponding products. Additionally, a reaction using substrates containing a nucleophilic phenoxy group within the same molecule also produces the corresponding dihydrofuran.     

Selective palladium-catalyzed amination of β-chloroacroleins by substituted anilines

β-Chloroacroleins can undergo a selective amination on their chloro position under palladium catalysis; in those conditions, no imine formation was observed. Their coupling with anilines carrying electron-donating or electron-withdrawing substituents proceeds in moderate to good yields and steric hindrance does not seem to be a limitation as o-substituted anilines react readily.     

Preparation of substituted benzoyltrimethylsilanes by the palladium-catalyzed silylation of substituted benzoyl chlorides with hexamethyldisilane

A direct preparative route to benzoyltrimethylsilane has been found by the reaction of benzoyl chloride with hexamethyldisilane in the presence of a specified palladium(II) complex as catalyst.     

Regioselective syntheses of substituted pteridines

Conclusions 7-Alkyl- or a mixture of 6- and 7-alkylpteridines are formed when 2,5,6-triamino-4-hydroxypyrimidine and tetraaminopyrimidine are reacted with N-substituted -aminoketones in aqueous medium in the presence of piperidine. The cyclocondensation of the indicated pyrimidines with N-acetyl--aminopropionaldehyde in the presence of Et₃N leads to 6-methylpterin and 2,4-diamino-6-methylpteridine.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 11, pp. 2626–2628, November, 1981.     

Synthesis of substituted naphthalenes by the palladium-catalyzed annulation of internal alkynes

[reaction: see text] A variety of substituted naphthalenes have been prepared by the palladium-catalyzed carboannulation of internal alkynes. This method (1) forms two new carbon-carbon bonds in a single step, (2) accommodates a variety of functional groups, and (3) affords excellent yields of highly substituted naphthalenes.     

One-pot synthesis of carbazoles by palladium-catalyzed N-arylation and oxidative coupling

One-pot N-arylation and oxidative coupling can be promoted by a common palladium catalyst in the presence of appropriate additives: palladium-catalyzed N-arylation of anilines with aryl triflates under the standard conditions followed by addition of acetic acid under oxygen or air atmosphere afforded various types of functionalized carbazoles in good to excellent yields.     

Selectively substituted thiophenes and indoles by a tandem palladium-catalyzed multicomponent reaction

A variety of di- and trisubstituted thiophenes were synthesized by a one-pot palladium-catalyzed ortho-alkylation sequence terminated by either Heck or C-H coupling. Initial results toward the functionalization of indoles are also presented.     

Efficient synthesis of ureas by direct palladium-catalyzed oxidative carbonylation of amines

A general synthesis of symmetrically disubstituted ureas and trisubstituted ureas by direct Pd-catalyzed oxidative carbonylation of primary amines or of a mixture of a primary and a secondary amine, respectively, with unprecedented catalytic efficiencies for this kind of process, is reported. Reactions are carried out at 90-100 degrees C in DME as the solvent in the presence of PdI(2) in conjunction with an excess of KI as the catalytic system and under 20 atm of a 4:1 mixture of CO and air. In some cases, working in the presence of an excess of CO(2) (40 atm) in addition to CO and air (60 atm total) had a beneficial effect on substrate reactivity and product yield. Cyclic five-membered and six-membered ureas were easily formed from primary diamines. The methodology has been successfully applied to the synthesis of pharmacologically active ureas, such as those deriving from alpha-amino esters or urea NPY5RA-972, a potent antagonist of the neuropeptide Y5 receptor.     

Highly regioselective synthesis of substituted tetrahydroquinolines by palladium-catalyzed cyclization of substituted 2-amidophenylmalonates with 1,4-diacetoxybut-2-ene

The reaction of 2-amidophenylmalonates with 1,4-diacetoxybut-2-ene in the presence of a palladium catalyst is described. Substituted tetrahydroquinolines having a vinyl group at the 3- or 2-position were synthesized, in which the regioselectivities of the double allylic substitution reactions have been altered depending on the substituent on the amino group.     

Synthesis of substituted naphthalenes and carbazoles by the palladium-catalyzed annulation of internal alkynes

An efficient synthesis of highly substituted naphthalenes has been developed by the palladium-catalyzed annulation of a variety of internal alkynes, in which two new carbon-carbon bonds are formed in a single step under relatively mild reaction conditions. This method has also been used to synthesize carbazoles, although a higher reaction temperature is necessary. The process involves arylpalladation of the alkyne, followed by intramolecular Heck olefination and double-bond isomerization. This method accommodates a variety of functional groups and affords the anticipated highly substituted naphthalenes and carbazoles in good to excellent yields.     

Synthesis of unsymmetrically substituted bipyridines by palladium-catalyzed direct C-H arylation of pyridine N-oxides

Substituted bipyridines were efficiently prepared by direct coupling between pyridine N-oxides and halopyridines using a palladium catalyst. Pyridine N-oxides with electron-withdrawing substituents gave the best yields. This method allows the convenient preparation of 2,2'-, 2,3'-, and 2,4'-bipyridines which are useful as functionalized ligands for metal complexes or as building blocks for supramolecular architectures.     

Solution- and solid-phase syntheses of substituted guanidinocarboxylic acids

A library of guanidine-based compounds was produced to mimic the lead compound 1, which is a substance known to have intensely sweet-taste characteristics. Libraries of guanidinocarboxylic acids were therefore prepared via two synthetic methods. The solid-phase method involving trapping of solution-phase carbodiimides by supported amines was used to produce N,N'-dialkyl derivatives (Scheme 1). The second solid-phase method, featuring supported carbodiimides and solution-phase amines (Scheme 2), was devised to prepare N,N'-disubstituted and N,N',N'-trisubstituted guanidinocarboxylic acids. A small collection of guanadinoacetic acid dimers and trimers was also prepared, but this time via a solution-phase coupling of carbodiimides to a polyamine linker.     

Concise syntheses of bacteriohopanetetrol and its glucosamine derivative

This study describes the syntheses of bacteriohopanetetrol and its glucosamine derivative through a key direct coupling of a ribose derivative to the hopane skeleton.