Synthesis of alpha-hydrazino ketones via regio- and stereoselective electrophilic amination of manganese enolates and enamines

A straightforward procedure for the regio- and stereoselective synthesis of alpha-hydrazino ketones is described. Manganese enolates and manganese enamines derived from ketones and from the corresponding N-sulfinylimines react with azodicarboxylate esters (DTBAD and DEAD) in a regioselective fashion to afford in good to excellent yields the kinetic alpha-hydrazino ketones as sole or highly prevalent products. When enantiopure N-sulfinyl manganese enamines were used the stereoselectivity of these reactions ranged from 40% to 68% ee.     

Highly regio- and stereoselective synthesis of indene derivatives via electrophilic cyclization

[reaction: see text] Indene or naphthalene derivatives are readily prepared in moderate to excellent yields with high regio- and stereoselectivity under very mild reaction conditions by the reaction of acetylenic malonates and ketones with I2, ICl, or NIS. The resulting iodides can be further elaborated using palladium-catalyzed coupling reactions.     

Synthesis of seven-membered lactones via nickel- and zinc-catalyzed highly regio- and stereoselective cyclization of 2-iodobenzyl alcohols with propiolates

A new class of substituted seven-membered lactones 3 were conveniently synthesized via cyclization of o-iodobenzyl alcohol 1 (o-IC(6)H(4)CH(2)OH) with various propiolates 2 (RC triple bond CCOOMe) in the presence of Ni(dppe)Br(2) and Zn powder in acetonitrile at 80 degrees C. The catalytic reaction is highly regio- and stereoselective affording seven-membered lactones in moderate to good yields. This methodology can be successfully extended to various substituted o-iodobenzyl alcohols. An intermediate 7 was obtained from the reaction of 1a with methyl 2-octynoate (2a) in the presence of Ni(dppe)Br(2) and Zn at room temperature. A mechanism involving an unusual E/Z isomerization of the carbon-carbon double bond of 7 prior to lactone formation is proposed to account for the catalytic reaction.     

Ruthenium-mediated regio- and stereoselective alkenylation of pyridine

A novel alkenylation reaction of pyridine is developed. Heating a cationic ruthenium vinylidene complex [CpRu(=C=CHR)(PPh(3))(2)]PF(6) in pyridine at 100-125 degrees C for 24 h affords (E)-2-alkenylpyridine. Initially, pyridine coordinates to ruthenium by displacement of one of the phosphine ligands. Then, [2 + 2] heterocycloaddition occurs to form a four-membered ruthenacyclic complex. Deprotonation of the beta-hydrogen affords a neutral pi-azaallyl complex. Protonolysis furnishes the product. As a result, a vinylidene group is inserted into the alpha C-H bond of pyridine. The alkenylation reaction is made catalytic in ruthenium by the use of (alkyn-1-yl)silane as the vinylidene source. Treatment of (alkyn-1-yl)trimethylsilane with pyridine in the presence of a cationic ruthenium complex [CpRu(PPh(3))(2)]PF(6) affords the corresponding (E)-2-alkenylpyridine in good yield in a regio- and stereoselective manner.     

Synthesis of cis-1,2-dichlorovinylsulfones via Fe-catalyzed regio- and stereoselective addition of sulfonyl chlorides to aromatic chloroalkynes

An iron-catalyzed regio- and stereoselective chlorosulfonylation of aryl chloroalkynes has been described, producing cis-1,2-dichlorovinylsulfones in satisfactory yields with good to excellent stereoselectivity (Z/E up to 95:5). A variety of functional groups such as F, NO₂, Cl, Br, OMe, and t-Bu are found to be compatible under the reaction conditions.     

Two-step regio- and stereoselective synthesis of cis-vinylstannanes

Herein we describe a novel stereoselective synthesis of cis-vinylstannanes employing the widely established Li/Te exchange pathway. In contrast to previously reported methods of cis-selective hydrostannation (i.e., ZrCl4), this method demonstrates compatibility toward oxygenated substrates.     

Synthesis of regio- and stereoselective alkoxy-substituted spirobifluorene derivatives for blue light emitting materials

Three new octyloxy substituted spirobifluorenes, 2,7-diphenyl-3′,6′-bis(octyloxy)-9,9′-spirobifluorene (DPBSBF, 1a), 2,7-dibiphenyl-3′,6′-bis(octyloxy)-9,9′-spirobifluorene (DBBSBF, 1b) and 2,7-diterphenyl-3′,6′-bis(octyloxy)-9,9′-spirobifluorene (DTBSBF, 1c) were prepared. All the compounds had been fully characterized by ¹H and ¹³C NMR, UV-Vis, DSC, mass spectrometry and gave satisfactory elemental analyses. They possessed good solubility in common organic solvents and good homogeneous film formation. The optical energy band gap of DBBSBF was 3.27 eV between the HOMO energy level, 5.85 eV, measured by UPS and the LUMO, 2.58 eV, calculated from absorption spectrum. A blue organic light emitting diode (OLED) based on the structure of ITO/TPD (60 nm)/DBBSBF (40 nm)/Alq₃ (20 nm)/LiF (1 nm)/Al (100 nm) showed good performance. The luminance of 3125 cd/m² was observed at a drive voltage of 12.8 V and the colour coordinate in CIE chromaticity was (0.14, 0.12). The external quantum efficiency was obtained to be 2.8% at 100 cd/m².     

Highly regio- and stereoselective synthesis of 1,3-enynes from unactivated ethylenes via palladium-catalyzed cross-coupling

An efficient procedure for regio- and stereoselective synthesis of a series of conjugated enynes by a simple Pd-catalyzed cross-coupling reaction of unactivated ethylenes and ethynyl bromide has been developed. The reaction proceeds smoothly in DMF to give the corresponding products in good to excellent yields. The protocol can tolerate a broad range of functional groups on the substrates.     

Novel efficient routes to heparin monosaccharides and disaccharides achieved via regio- and stereoselective glycosidation

A new methodology for the synthesis of heparin building blocks has been developed. We describe novel efficient routes to both L-iduronic acid and D-glucuronic acid acceptors. Glycosylation with thioglycosides donors gave corresponding disaccharides in a regio- and stereoselective fashion. An improved approach to synthesizing azido-glucose thioglycoside donor to render azido-sugar from mannose via nucleophilic substitution is described. [reaction: see text]     

Tandem regio- and stereoselective organocuprate-mediated bis-allylic substitutions

anti-5-Acetoxy-4-halo-alpha,beta-enoates undergo sequential or tandem reactions with two different magnesium cuprate reagents to afford anti-2,3-dialkyl-4,5-enoates in high chemical yield and with excellent diastereoselectivity. The one-pot tandem procedure can be achieved with 30 mol % of CuCN and affords a rapid stereoselective combinatorial approach to vicinal disubstituted gamma,delta-enoates containing functionality at either end of the carbon chain for subsequent functional group elaboration. The methodology should provide a powerful practical strategy for acyclic stereoselection.     

Synthesis of vinylpyrroles, vinylfurans and vinylindoles via a Brønsted acid catalyzed highly regio- and stereoselective cis-hydroarylation of ynamides

A highly regio- and stereoselective Brønsted acid-catalyzed coupling of ynamides and aromatic heterocycles, such as pyrroles, furans, and indoles is described. This process is the equivalent of hydroarylation of ynamides, and leads to the efficient syntheses of an array of vinylheterocycles. Diels-Alder reaction between the vinylindoles and DMAD afforded carbazole derivatives in good yields.     

Organocatalyzed regio- and stereoselective diamination of functionalized alkenes

The first organocatalyzed diamination reaction of alkenes with N,N-dichlorotoluenesulfonamide (TsNCl₂) and acetonitrile as nitrogen sources was reported. The catalytic diamination reaction was convenient to carry out, resulting in imidazoline products with good yields and excellent regio- and stereoselectivities. Several other organic molecules were also tried as catalyst for this reaction and good results were achieved. A new one-pot synthesis of vicinal diamines via the current PPh₃-catalyzed diamination and the hydrolysis of resulting imidazoline products with SnCl₄ as promoter was also established.     

Pt-catalyzed regio- and stereoselective pyridylthiolation of terminal alkynes

Three-component cross-coupling reactions among 3-iodopyridynes, terminal alkynes and ArSK took place in the presence of Pt-catalyst to give pyridine derivatives with conjugated vinyl groups in moderate yields.     

Platinum-catalyzed regio- and stereoselective arylthiolation of internal alkynes

Unsymmetrical internal alkynes such as ethyl phenylpropiolate (2b) successfully underwent Pt-catalyzed decarbonylative arylthiolation by thioesters. The regio- and stereoselective insertion of 2b into an S-Pt bond was confirmed by reaction with a platinum complex with an S-Pt-Cl framework.     

Palladium-catalyzed regio- and stereoselective hydrosilylation of electron-deficient alkynes

Highly regio- and stereoselective hydrosilylation applicable to a broad range of electron-deficient alkynes has been established using palladium catalysis. The synthetic utility of the method has been demonstrated by further transformations of α-silylalkenes, particularly Hiyama coupling and stereoinverting iododesilylation followed by Suzuki-Miyaura coupling, which enables stereodivergent syntheses of α-arylenoates.     

Cu-catalyzed regio- and stereoselective sulfonylation of multi-substituted allenes

Regio- and stereoselective sulfonylation of allenes under Cu catalysis is described. Allenyl sp carbons exclusively react with TsCN to give the corresponding alkenyl sulfones. The reaction is initiated by addition of tosyl radical to form benzyl radical intermediates, which determines the reaction pathway. The structure of the products is highly dependent on the substituents on allenes.     

A highly regio- and stereoselective synthesis of internal olefins via an elimination of trimethylstannyl group

Internal reaction of secondary alkyltin(IV) compounds having thionium ion gave internal trans olefins with high yield and regio- and stereoselectivity via 1,5- or 1,6-transfer of a hydride β to the trialkylstannyl group.     

Highly regio- and stereoselective synthesis of tetrasubstituted cyclobutenes via cyclodimerization of alkynes mediated by zirconium

Zirconium-induced cyclodimerization of a variety of heteroaryl-substituted alkynes is described. This method provides a facile synthesis of tetrasubstituted cyclobutenes with high regio- and diastereoselectivity. A ligand-induced reductive elimination mechanism accounting for this novel cyclodimerization is suggested.     

Ruthenium(II)-catalyzed regio- and stereoselective hydroarylation of alkynes via directed C-H functionalization

The ruthenium-catalyzed hydroarylation of alkynes with benzamides proceeds regio- and stereoselectively through a directed C-H bond cleavage. Preliminary mechanistic investigations indicate that the reaction involves amide-directed ortho-metalation, carbometalation of alkyne, and protonolysis. Similarly, phenylazoles also add to alkynes regioselectively.     

Synthesis of diverse heterocyclic scaffolds via tandem additions to imine derivatives and ring-forming reactions

A novel strategy has been developed for the efficient syntheses of diverse arrays of heterocyclic compounds. The key elements of the approach comprise a Mannich-type, multicomponent coupling reaction in which functionalized amines, aromatic aldehydes, acylating agents, and π- and organometallic nucleophiles are combined to generate intermediates that are then further transformed into diverse heterocyclic scaffolds via a variety of cyclization manifolds. Significantly, many of these scaffolds bear functionality that may be exploited by further manipulation to create diverse collections of compounds having substructures found in biologically active natural products and clinically useful drugs. The practical utility of this strategy was exemplified by its application to the first, and extraordinarily concise synthesis of the isopavine alkaloid roelactamine.