Site-Selective Double and Tetracyclization Routes to Fused Polyheterocyclic Structures by Pd-Catalyzed Carbonylation Reactions.

In this contribution, we report novel palladium-catalyzed carbonylative cascade approaches to highly functionalized polyheterocyclic structures. The Pd-catalyzed carbonylative process involves the regioselective insertion of one to three CO molecules and the sequential ordered formation of up to eight new bonds (one C-O, two C-C, five C-N). The exclusive formation of six-membered heterocycles is elucidated by detailed modeling studies.

An Unprecedented Pd-Catalyzed Carbonylative Route to Fused Furo[3,4-b]indol-1-ones.

A novel and efficient catalytic approach to functionalized furo[3,4-b]indol-1-ones is reported. It is based on a palladium-catalyzed sequential process involving an initial cyclization of 2-(hydroxypropyn-1-yl)anilines to form the indole moiety, followed by insertion of carbon monoxide and a second annulation step to build a lactone ring. In a single transformation, two fused heterocycles and three new bonds (C-N, C-C and C-O) are generated. The present methodology gives direct access to structurally complex molecules starting from readily available reagents.

A general and expedient synthesis of 5- and 6-membered cyclic carbonates by palladium-catalyzed oxidative carbonylation of 1,2- and 1,3-diols.

We present a general, practical, and efficient approach to 5- and 6-membered organic carbonates by palladium-catalyzed direct oxidative carbonylation of 1,2- and 1,3-diols, respectively. Reactions were carried out at 100 °C in N,N-dimethylacetamide as the solvent under 20 atm (at 25 °C; 1 atm=101.3 kPa) of a 4:1 v/v CO/air mixture in the presence of 0.5-2 mol % of PdI(2) and KI (KI/PdI(2) molar ratio=10). Excess dehydrating agent, such as trimethyl orthoacetate, was necessary in several cases to obtain appreciable results. The method could also be applied to the synthesis of a high-value-added glycerol carbonate from glycerol, a readily available raw material. When applied to α-D-glucose, a double carbonylation process took place, with direct formation of α-D-glucofuranose 1,2:5,6-dicarbonate.

Versatile synthesis of quinoline-3-carboxylic esters and indol-2-acetic esters by palladium-catalyzed carbonylation of 1-(2-aminoaryl)-2-yn-1-ols.

1-(2-Aminoaryl)-2-yn-1-ols, easily obtained by the Grignard reaction between 1-(2-aminoaryl)ketones and alkynylmagnesium bromides, were subjected to carbonylative conditions in the presence of the PdI2-KI catalytic system, in the presence and in the absence of an external oxidant. Under oxidative conditions (80 atm of a 4:1 mixture of CO-air, in MeOH as the solvent at 100 degrees C and in the presence of 2 mol % of PdI2 and 20 mol % of KI), 1-(2-aminoaryl)-2-yn-1-ols bearing a primary amino group were selectively converted into quinoline-3-carboxylic esters in fair to good yields [45-70%, based on starting 1-(2-aminoaryl)ketones], ensuing from 6-endo-dig cyclization followed by dehydration and oxidative methoxycarbonylation. On the other hand, indol-2-acetic esters, deriving from 5-exo-dig cyclization followed by dehydrating methoxycarbonylation, were selectively obtained in moderate to good yields [42-88%, based on starting 1-(2-aminoaryl)ketones] under nonoxidative conditions (90 atm of CO, in MeOH as the solvent at 100 degrees C and in the presence of 2 mol % of PdI2 and 20 mol % of KI), in the case of 1-(2-aminoaryl)-2-yn-1-ols bearing either a primary or secondary amino group and substituted with a bulky group on the triple bond.

Cascade reactions: a new synthesis of 2-benzofuran-2-ylacetamides by sequential Pd(0)-catalyzed deallylation-Pd(II)-catalyzed aminocarbonylative heterocyclization of 1-(2-allyloxyaryl)-2-yn-1-ols.

A general and efficient synthesis of 2-benzofuran-2-ylacetamides 5 starting from 1-(2-allyloxyaryl)-2-yn-1-ols 1, amines 4, and CO, in the presence of catalytic amounts of PdI2 in conjunction with PPh3 and KI, has been developed based on the "sequential homobimetallic catalysis" concept, that is, a process in which two different complexes of the same metal, but in two different oxidation states, promote two catalytic cycles in sequence. The first cycle corresponds to a Pd(0)-catalyzed aminodeallylation of 1 with formation of the free phenol 2, which then undergoes Pd(II)-catalyzed aminocarbonylative heterocyclization to give the final product 5.

An unprecedented Pd-catalyzed, water-promoted sequential oxidative aminocarbonylation-cyclocarbonylation process leading to 2-oxazolidinones.

An unprecedented, PdI2-catalyzed, sequential oxidative aminocarbonylation-cyclocarbonylation process, leading to 2-oxazolidinone derivatives 3 in good to excellent yields starting from readily available alpha,alpha-disubstituted 2-ynylamines 1 and secondary amines 2, is reported. In the case of an alpha-monosubstituted substrate, the initially formed 2-oxazolidinone derivative underwent shift of the double bond to give a 3H-oxazol-2-one derivative in excellent isolated yield.

Heterocyclic derivative syntheses by palladium-catalyzed oxidative cyclization-alkoxycarbonylation of substituted gamma-oxoalkynes.

4-Yn-1-ones containing different substituents, prop-2-ynyl alpha-ketoesters, and prop-2-ynyl alpha-ketoamides have been caused to react catalytically under oxidative carbonylation conditions to give tetrahydrofuran, dioxolane and oxazoline, dihydropyridinone, and tetrahydropyridinedione derivatives in satisfactory yields. Reactions were carried out in MeOH or MeCN/MeOH mixtures at 65-100 degrees C in the presence of catalytic amounts of PdI(2) in conjunction with KI under 32 bar (at 25 degrees C) of a 3:1 mixture of CO and air. Anti and syn 5-exo-dig cyclization modes account for the formation of different products. It has been found that cyclopentenone, dihydropyridinone, and tetrahydropyridinedione derivatives, formed when the reaction is carried out at higher temperature and for a longer time, can also be selectively obtained through an acid treatment of tetrahydrofuran and oxazoline derivatives involving an unusual rearrangement. The structures of 6-methoxy-2,2-dimethyl-3-oxo-5-phenyl-2,3-dihydropyridine-4-carboxylic acid methyl ester and 2,2,5-trimethyl-3,6-dioxo-1,2,3,6-tetrahydropyridine-4-carboxylic acid methyl ester have been confirmed by X-ray diffraction analysis.

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.

Synthesis of 4H-3,1-benzoxazines, quinazolin-2-ones, and quinoline-4-ones by palladium-catalyzed oxidative carbonylation of 2-ethynylaniline derivatives.

An effective and straightforward approach to the synthesis of 4H-3,1-benzoxazines 3 and 4, quinazolin-2-ones 5, and quinoline-4-one derivatives 6 and 7 is provided by palladium-catalyzed cyclization-alkoxycarbonylation of variously substituted 2-(trimethylsilanyl)ethynylaniline amide or urea derivatives 2. Reactions are carried out in 7:1 MeCN/MeOH at 65 or 75 degrees C in the presence of catalytic amounts of 10% Pd/C in conjunction with Bu(4)NI and KF and under 2.4 MPa of a 3:1 mixture of CO and air. Anti and syn 6-exo-dig cyclization modes account for the formation of the two stereoisomers. Isomerization of the vinylpalladium intermediate may occur as well. Formation of a double carbonylation product 7r and of a gem-dimethoxycarbonylation product 6s, whose structures have been determined by X-ray diffraction analysis, is justified through an unusual type of rearrangement.

A novel and efficient method for the Pd-catalysed oxidative carbonylation of amines to symmetrically and unsymmetrically substituted ureas.

A new method for the Pd-catalysed oxidative carbonylation of amines to symmetrically and unsymmetrically substituted ureas with unprecedented catalytic efficiencies for this kind of reaction has been developed.

An improved procedure for the palladium-catalyzed oxidative carbonylation of beta-amino alcohols to oxazolidin-2-ones.

A highly efficient oxidative cyclocarbonylation of beta-amino alcohols and 2-aminophenol to oxazolidin-2-ones has been achieved by using PdI(2) in conjunction with KI as the catalytic system in DME under relatively mild conditions (100 degrees C and 20 atm of a 4:1 mixture of CO and air).

Efficient and general synthesis of 5-(alkoxycarbonyl)methylene-3-oxazolines by palladium-catalyzed oxidative carbonylation of prop-2-ynylamides.

A variety of prop-2-ynylamides have been carbonylated under oxidative conditions to give oxazolines, oxazolines with chelating groups, and bisoxazolines bearing an (alkoxycarbonyl)methylene chain at the 5 position in good yields. The cyclization-alkoxycarbonylation process was carried out in alcoholic media at 50-70 degrees C and under 24 bar pressure of 3:1 carbon monoxide/air in the presence of catalytic amounts of 10% Pd/C or PdI2 in conjunction with KI. Cyclization occurred by anti attack of an oxygen function on the palladium-coordinated triple bond, followed by stereospecific alkoxycarbonylation, strictly resulting in E-stereochemistry. The structures of representative oxazolines and bisoxazolines have been determined by X-ray diffraction analysis.