IBX/Sc(OTf)3-promoted one-pot oxidative conjugate addition of allyltrimethylsilane to Baylis-Hillman adducts

Baylis-Hillman adducts undergo smooth one-pot oxidative Michael addition with allyltrimethylsilane in the presence of 2-iodoxybenzoic acid (IBX)/Sc(OTf)₃ under mild conditions to afford homoallyl β-ketoesters in good yields with high 1,4-selectivity.     

Ionic liquid-promoted one-pot oxidative Michael addition of TMSCN to Baylis-Hillman adducts

The first example of ionic liquid-promoted one-pot oxidative conjugate hydrocyanation of Baylis-Hillman adducts with trimethylsilyl cyanide (TMSCN) is reported. The oxidation of Baylis-Hillman adducts with IBX/[bmim]Br or isomerization-oxidation with NaNO₃/[Hmim]HSO₄ systems affords β-ketomethylene compounds or [E]-cinnamaldehydes, respectively. These α,β-unsaturated carbonyl compounds undergo Michael addition with TMSCN in the same vessel to afford the corresponding thermodynamically more stable β-cyanated products. Thermodynamically less stable 1,2-addition products were not formed. The present regioselective reactions are promoted by ionic liquids, which can be recycled easily for further use without any loss of efficiency.     

The first one-pot oxidative Michael reaction of Baylis-Hillman adducts with indoles promoted by iodoxybenzoic acid

Baylis-Hillman adducts undergo smooth, one-pot oxidative conjugate addition with indoles in the presence of 2-iodoxybenzoic acid (IBX) under neutral conditions to afford a new class of substituted indoles in good yields.     

The first one-pot oxidative 1,2-acetoxysulfenylation and 1,2-disulfenylation of Baylis-Hillman alcohols in an ionic liquid

The first example of tandem oxidation and 1,2-acetoxysulfenylation/1,2-disulfenylation of Baylis-Hillman (BH) alcohols to afford 1,2-acetoxysulfides/1,2-dithioethers is reported. The reaction involves oxidation of BH alcohols with IBX in [bmim]Br to give β-ketomethylene compounds in situ followed by CuI-imidazole-catalyzed 1,2-acetoxysulfenylation with an organodisulfide and acetic acid under air to afford vicinal acetoxysulfides in excellent yields with complete regioselectivity. In the absence of the Cu(I) catalyst, 1,2-disulfenylation takes place to give vicinal dithioethers in 81-90% yields.     

Ionic liquid [Hmim]HSO4-promoted one-pot oxidative conjugate addition of sulfur-centred nucleophiles to Baylis-Hillman adducts

The first example of the one-pot oxidative conjugate addition of sulfur-centred nucleophiles to Baylis-Hillman adducts is reported. The reaction involves oxidation of Baylis-Hillman adducts with NaNO₃ in the Brønsted acidic ionic liquid [Hmim]HSO₄ to give [E]-α-cyanocinnamaldehydes followed by conjugate hydrothiocyanation/hydrosulfenylation with NH₄SCN/PhSH to afford the corresponding β-thiocyanato (or β-phenylsulfenyl)-α-cyanohydrocinnamaldehydes diastereoselectively in 76-89% yields in a one-pot procedure. After isolation of the product, the ionic liquid [Hmim]HSO₄ could be easily recycled for further use.     

Direct one-pot introduction of 2-methylpyridines to Baylis-Hillman adducts via base-mediated 3-aza-Cope rearrangement

An efficient and regioselective introduction method of 2-methylpyridines to the secondary position of Baylis-Hillman adducts has been developed. A base treatment of 2-methylpyridinium salt of Baylis-Hillman bromide generated N-allylenamine intermediate which underwent a facile 3-aza-Cope rearrangement under mild conditions to produce the product.     

Simple, facile and one-pot conversion of the Baylis-Hillman acetates into 3,5,6-trisubstituted-2-pyridones

A facile route for the synthesis of novel 3,5,6-trisubstituted-2-pyridones from the acetylated Baylis-Hillman esters with β-enamino esters or β-enamino nitriles in one pot with good yields is described.     

Synthesis of N-aryl-3-(arylimino)-3H-indol-2-amines via hypervalent iodine promoted oxidative diamination of indoles

A direct and fast oxidative diamination of substituted indoles with anilines was realized by using 1-fluoro-1,2-benziodoxol-3(1H)-one under mild conditions. This protocol could provide a wide range of synthetically valuable N-aryl-3-(arylimino)-3H-indol-2-amine derivatives under peroxide-free conditions within 30?min in up to 91% yields.     

Synthesis of poly-substituted tetrahydropyridines from Baylis-Hillman adducts modified with N-allylamino group via radical cyclization

An expedient method was developed for the synthesis of 1,4,5,6-tetrahydropyridines by radical cyclization protocol involving consecutive 1,5-hydrogen transfer and double bond isomerization process starting from Baylis-Hillman adducts.     

Synthesis of N-tosyl-3,3,4-trisubstituted pyrrolidine derivatives starting from the Baylis-Hillman adducts via radical cyclization

N-Tosyl-3,3-disubstituted-4-vinylpyrrolidine derivatives 3a-c were synthesized via radical cyclization from the modified Baylis-Hillman adducts 2. The required starting materials 2a-c were prepared in moderate yields from the Baylis-Hillman adducts in three steps: (i) acetylation of the Baylis-Hillman adducts, (ii) S_N2′ reaction with tosylamide to prepare 1, and (iii) alkylation with 1,4-dibromo-2-butene.     

IBX/TEAB-mediated oxidative dimerization of thioamides: synthesis of 3,5-disubstituted 1,2,4-thiadiazoles

Thioamides undergo oxidative dimerization on treatment with hypervalent iodine(V)-containing reagents, particularly o-iodoxybenzoic acid (IBX), in the presence of tetraethylammonium bromide (TEAB) to generate 3,5-disubstituted 1,2,4-thiadiazoles in excellent yield.     

An expedient aralkylation of Baylis-Hillman adduct via the Pd-catalyzed decarboxylative protonation strategy

An expedient protocol of aralkylation of Baylis-Hillman adducts has been developed. This method used Pd-catalyzed decarboxylative protonation strategy to the allyl ester precursor that was made from the Baylis-Hillman adduct and allyl phenylacetate.     

Synthesis of methyl 9-phenyl-7H-benzocycloheptene-6-carboxylates from Baylis-Hillman adducts: use of intramolecular Friedel-Crafts alkenylation reaction

We developed a facile synthetic method for 9-phenyl-7H-benzocycloheptene derivatives from the Baylis-Hillman adducts. Our method involved intramolecular Friedel-Crafts alkenylation reaction of triple bond-tethered methyl cinnamates.     

Organic reactions in water: an efficient one-pot synthesis of acyloxiranes from Baylis-Hillman adducts using hypervalent iodine

Treatment of Baylis-Hillman adducts with iodosobenzene (PhIO) in the presence of a catalytic amount of KBr in water at room temperature afforded the corresponding acyloxiranes in good yields.     

An efficient synthesis of Baylis-Hillman adducts of acrylamide: Pd-catalyzed hydration of Baylis-Hillman adducts of acrylonitrile

An efficient palladium-catalyzed two-step protocol for the synthesis of Baylis-Hillman adducts of acrylamide was developed. The method involved the preparation of Baylis-Hillman adducts of acrylonitrile and a Pd-catalyzed hydration of nitrile with acetaldoxime.     

Chiral hypervalent iodine-catalyzed enantioselective oxidative Kita spirolactonization of 1-naphthol derivatives and one-pot diastereo-selective oxidation to epoxyspirolactones

We demonstrate here the rational design of a conformationally flexible C₂-symmetric iodosylarene 8g based on secondary n-σ^∗ or hydrogen-bonding interactions as a chiral catalyst for the enantioselective Kita oxidative spirolactonization of 1-naphthol derivatives 5. Iodosylarenes 8 were generated in situ from iodoarenes 7 and mCPBA as a co-oxidant. Furthermore, epoxyspirolactone 15 was obtained by the one-pot oxidation of 5 with mCBPA in the presence of 7g. Thus, the enantioselective oxidation of 5 to 6 and the successive enantio- and diastereo-selective oxidation of 5 to 15 proceeded in good yields when we controlled the amount of mCPBA.     

Synthesis of poly-substituted pyrroles starting from the Baylis-Hillman adducts

We synthesized poly-substituted pyrrole derivatives 4a-e, 7a-c and 10a-d from the reaction of phenacyl bromide and the aza-Baylis-Hillman adducts 1a-d or their rearranged derivatives 5a-e. The pyrroles were synthesized via the successive N-alkylation, Michael addition, elimination of p-toluenesulfinic acid and oxidative aromatization processes.     

Synthesis of poly-substituted benzenes starting from Baylis-Hillman adducts: DBU-assisted unusual dehydrogenation

Poly-substituted benzenes were synthesized in moderate yields starting from the Baylis-Hillman adducts. The synthesis was carried out by two steps via first synthesis of cyclohexene intermediates and the following DBU-assisted unusual dehydrogenation.     

CeCl3·7H2O/IBX-promoted oxidation of 3-alkylindoles to 3-hydroxyoxindoles

3-Alkylindoles undergo smooth oxidation with IBX in the presence of CeCl₃·7H₂O in aqueous acetonitrile at ambient temperature to afford the corresponding 3-hydroxyoxindoles in high yields. This method is very useful for the direct preparation of 3-hydroxyoxindoles from 3-alkylindoles. Operational simplicity, mild and neutral reaction conditions in aqueous solution are the key features of this protocol.     

IBX/I2-mediated oxidation of alkenes and alkynes in water: a facile synthesis of α-iodoketones

The conversion of alkenes into α-iodoketones has been achieved in good yields and with high regioselectivity by means of iodohydrin formation and subsequent oxidation with 2-iodoxybenzoic acid (IBX) under mild conditions. Aromatic alkynes are also converted into their corresponding α-iodoketones under similar conditions.