Molecular Iodine as a Catalyst for Alkene Difluorination.

The difluorination reaction of alkenes catalyzed by molecular iodine was revealed for the first time. This difluorination reaction affords a simple and practical experimental method and can be applied to many aliphatic and aromatic alkenes bearing synthetically useful functional groups, such as ester, amide, hydroxy, and aryl groups. Preliminary mechanistic studies of this alkene difluorination suggest the existence of two catalytic cycles: the IF-driven cycle and the catalytic cycle by the IF adduct.

Iodine-Mediated Fluorination of Alkenes with an HF Reagent: Regioselective Synthesis of 2-Fluoroalkyl Iodides.

Fluorination reaction of alkenes with iodine and HF·pyridine complex (pyr·9HF) was performed under mild conditions in the presence of K2S2O8 or Na2S2O8 as an oxidant. Aliphatic and aromatic alkenes underwent iodofluorination to give the iodofluorinated products with high regioselectivity. The substitution reactions of the iodofluorinated product by nitrogen, sulfur, and oxygen nucleophiles indicated further applications as a building block for synthesis of 2-fluoroalkyl-substituted compounds.

Synthesis of [1]Benzothieno[3,2- b][1]benzothiophene Derivatives via Successive Iodocyclization/Photocyclization of Alkynes.

A new synthetic method for [1]benzothieno[3,2- b][1]benzothiophene derivatives (BTBTs) was developed. The present method consists of iodocyclization of 1,2-bis(2-methylthiophenyl)ethynes and photolysis of 3-iodo-(2-methylthiophenyl)benzo[ b]thiophenes. With 1,2-bis(2-methylthiophenyl)ethynes treated with I2/PhI(OAc)2 in CH2Cl2 at room temperature, selective cyclization at sulfur took place to give 3-iodo-(2-methylthiophenyl)benzo[ b]thiophenes in good yields. Irradiation of the iodinated benzo[ b]thiophenes with a high-pressure Hg lamp (>290 nm) provided BTBTs in good yields. Furthermore, the present method was applied to the synthesis of bis[1]benzothieno[2,3- d;2',3'- d']benzo[1,2- b;4,5- b']dithiophene (BBTBDT).

Difluorination of Functionalized Aromatic Olefins Using Hypervalent Iodine/HF Reagents.

The hypervalent iodine/HF reagent consisting of PhIO and HF·py was found to be effective for fluorination of functionalized aromatic olefins bearing synthetically important carbonyl and hydroxyl groups. Fluorination of 1,3-diphenyl-2-propen-1-one with PhIO/HF·py reagent in CH2Cl2 at room temperature gave 3,3-difluoro-1,2-diphenyl-1-propanone in high yield. Other α-aryl-α,ß-unsaturated ketones underwent the fluorination to yield aryl 2,2-difluoroethyl ketone derivatives in good to high yields. Catalytic fluorination of α-aryl-α,ß-unsaturated ketones using a p-TolI/HF·py/mCPBA reagent system also worked well. Moreover, the fluorination of cinnamyl alcohol derivatives by PhIO/HF·py reagent proceeded smoothly to afford 2-aryl-3,3-difluoro-1-propanols in moderate yields.

Synthesis of ß-Fluorovinyliodonium Salts by the Reaction of Alkynes with Hypervalent Iodine/HF Reagents.

The reaction of alkynes with PhIO and Py·HF followed by treatment with BF3·OEt2 gave ß-fluorovinyliodonium tetrafluoroborates in good to high yields. More conveniently, the reaction using PhI and Py·HF in the presence of m-CPBA also afforded ß-fluorovinyliodonium tetrafluoroborates in good yields. These methods have the advantages that ß-fluorovinyliodonium salts can be prepared without ArIF2.

Hypervalent Iodine/Triflate Hybrid Benzdiyne Equivalents: Access to Controlled Synthesis of Polycyclic Aromatic Compounds.

The 1,4-benzdiyne equvalent, [2,5-bis(trimethylsilyl)-4-(trifyloxy)phenyl](phenyl)iodonium triflate, was prepared from sodium 2,4,5-trichlorophenoxide. The chemoselective generation of an aryne from the side of the phenyliodonio group was observed after treatment with a fluoride ion. Double cycloaddition of 1,4-benzdiyne with different arynophiles was conducted in one pot, giving bis-cycloadducts in high yields. Similarly, the 1,3-benzdiyne equivalent bearing phenyliodonio and triflate groups was prepared from sodium 2,3,6-trichlorophenoxide. The 1,3-benzdiyne equivalent also underwent the chemoselective stepwise generation of arynes and the double cycloaddition with different arynophiles. These hybrid benzdiyne equivalents provided the double cycloadducts in high yields and enabled the convenient one-pot procedure for synthesis of polycyclic aromatic compounds.

ortho-Selective C-H addition of N,N-dimethyl anilines to alkenes by a yttrium catalyst.

The efficient and selective ortho-alkylation of N,N-dimethyl anilines via C-H addition to alkenes was achieved for the first time using a cationic half-sandwich yttrium catalyst. This protocol constitutes a straightforward and atom-economical route for the synthesis of a new family of tertiary aniline derivatives with branched alkyl substituents, which are otherwise difficult to obtain. DFT calculation studies suggest that the interaction between the yttrium atom and the NMe2 group plays an important role and the intramolecular C-H activation through a σ-bond metathesis pathway is the rate-determining step, which is consistent with the experimental KIE observations.

Scandium-catalysed intermolecular hydroaminoalkylation of olefins with aliphatic tertiary amines.

A homoleptic scandium trialkyl complex in combination with a borate compound served as an excellent catalyst for the C-H addition of aliphatic tertiary amines to olefins. This highly regiospecific, 100% atom efficient C-H bond alkylation reaction was applicable to a wide variety of tertiary amines and olefins, including functionalised styrenes and unactivated α-olefins. This work represents the first example of rare-earth catalysed olefin hydroaminoalkylation and also the first example of catalytic C-H addition of aliphatic tertiary amines to olefins with any catalyst.

Hypervalent Iodine-Mediated Fluorination of Styrene Derivatives: Stoichiometric and Catalytic Transformation to 2,2-Difluoroethylarenes.

Fluorination of styrene derivatives with a reagent system composed of µ-oxo-bis[trifluoroacetato(phenyl)iodine] and a pyridine·HF complex gave the corresponding (2,2-difluoroethyl)arenes in good yields. Similarly, the reagent of PhI(OCOCF3)2 and the pyridine·HF complex acted as a fluorinating agent for styrene derivatives. The fluorination of styrene derivatives with the pyridine·HF complex underwent under catalytic conditions using 4-iodotoluene as a catalyst and m-CPBA as a terminal oxidant.

Palladium-Catalyzed Desilylative Acyloxylation of Silicon-Carbon Bonds on (Trimethylsilyl)arenes: Synthesis of Phenol Derivatives from Trimethylsilylarenes.

A strategy for desilylative acetoxylation of (trimethylsilyl)arenes has been developed in which (trimethylsilyl)arenes are converted into acetoxyarenes. The direct acetoxylation is performed in the presence of 5 mol % of Pd(OAc)2 and PhI(OCOCF3)2 (1.5 equiv) in AcOH at 80 °C for 17 h. The acetoxyarenes are obtained in good to high yields (67-98%). The synthetic utility is demonstrated with a one-pot transformation of (trimethylsilyl)arenes to phenols by successive acetoxylation and hydrolysis. Furthermore, desilylative acyloxylation of 2-(trimethylsilyl)naphthalene using several carboxylic acids has been conducted.

Drastic effect of bidentate phosphine ligands on Pd-catalyzed hydroarylation of ethyl propiolate: a simple route to arylbutadienes.

Palladium complexes with bidentate phosphine ligands, Pd(dppe)(OAc)(2) and Pd(dppm)(OAc)(2), were found to be effective catalysts for reactions of simple arenes with ethyl propiolate, affording arylbutadiene derivatives selectively.

Practical and convenient synthesis of coumarins from phenols and propiolic acid esters.

This protocol describes the synthesis of 6,7-methylenedioxy-4-phenylcoumarin from sesamol and ethyl phenylpropiolate using a Pd(OAc)2 catalyst to illustrate coumarin synthesis. This procedure is simple and easy and can be applied to the synthesis of other coumarins that have electron-rich phenol groups. The reaction is conducted by stirring a solution of Pd(OAc)2, sesamol and ethyl phenylpropiolate in trifluoroacetic acid at room temperature (15-20 degrees C) under atmospheric conditions. This protocol can be completed in 3 d.