Diastereoselective vinyl addition to chiral hydrazones via tandem thiyl radical addition and silicon-tethered cyclization

A diastereoselective method for addition of a vinyl group to alpha-hydroxy hydrazones under neutral tin-free radical cyclization conditions, leading to substituted vinylglycinols, is presented. Tandem thiyl radical addition/cyclization upon a silicon-tethered vinyl group followed by treatment with potassium fluoride accomplishes a one-pot neutral vinyl addition process to afford acyclic allylic anti-hydrazino alcohols in good yield.     

Synthesis of (±)-oleocanthal via a tandem intramolecular Michael cyclization-HWE olefination

A synthesis of racemic oleocanthal has been accomplished in 11 steps from 1,3 propanediol by a key tandem intramolecular Michael cyclization-Horner-Wadsworth-Emmons olefination.     

Enantioselective Michael addition to vinyl phosphonates via hydrogen bond-enhanced halogen bond catalysis

An asymmetric Michael addition of malononitrile to vinyl phosphonates was accomplished by hydrogen bond-enhanced bifunctional halogen bond (XB) catalysis. NMR titration experiments were used to demonstrate that halogen bonding, with the support of hydrogen-bonding, played a key role in the activation of the Michael acceptors through the phosphonate group. This is the first example of the use of XBs for the activation of organophosphorus compounds in synthesis. In addition, the iodo-perfluorophenyl group proved to be a better directing unit than different iodo- and nitro-substituted phenyl groups. The developed approach afforded products with up to excellent yields and diastereoselectivities and up to good enantioselectivities.

An asymmetric Michael addition of malononitrile to vinyl phosphonates was accomplished by hydrogen bond-enhanced bifunctional halogen bond (XB) catalysis.     

Conjugate addition of alkyl groups to α,β-unsaturated sulfoxides via Michael addition of nitroparaffins and subsequent denitration with tributyltin hydride

Michael addition of nitroparaffins to α,β-unsaturated sulfoxides is well effected in the presence of DBU. The nitro group in the adduct is replaced by hydrogen with Bu₃SnH without influence to the sulfinyl function. The overall reations provide an efficient method for the conjugate addition of alkyl groups to α,β-unsaturated sulfoxides.     

Catalyzed double Michael addition of anilines to vinyl sulfone

Substituted anilines and vinyl sulfone undergo a facile double Michael addition to form substituted phenylthiomorpholine dioxide, catalyzed with AlCl₃ or H₃PO₄. Scope and conditions were explored.     

A Novel Approach towards 2,3,5-Trisubstituted Thiophenes via tandem Michael addition/intramolecular Knoevenagel condensation

Starting from the easily available, highly functionalized acetylenic ketories 4a–i (Scheme 1), novel 2,3,5-trisubstituted thiophenes 1a–i (Scheme 2) were synthesized in good yields using a tandem Michael-addition/intramolecular Knoevenagel-condensation strategy, featuring Cs₂CO₃/MgSO₄ (1:2) as an efficient base to effect the cyclization. Subsequent simple one-step transformations yielded 2,3-disubstituted thiophene-5-carbaidehydes 7a–c , carboxylic-acid derivatives 8, 9 , and 11 , and alcohol 10 (Scheme 3). These molecules constitute interesting novel thiophene-containing building blocks, useful for the preparation of low-molecular-weight compound libraries by combinatorial and parallel-chemistry techniques.     

First organocatalyzed asymmetric Michael addition of aldehydes to vinyl sulfones

[reaction: see text] The first asymmetric direct Michael addition of aldehydes to vinyl sulfones catalyzed by N-iPr-2,2'-bipyrrolidine is described. 1,4-Adducts are obtained in good yields and enantioselectivities. The determination of absolute configuration allowed us to postulate a Si,Si transition state model, as shown previously for nitroolefins.     

Tandem Michael addition/ylide olefination reaction for the synthesis of highly functionalized cyclohexadiene derivatives

A tandem Michael addition/ylide olefination for the rapid creation of highly functionalized cyclohexadiene is developed. The tandem annulation reactions afford versatile cyclohexadienes in good to excellent isolated yields. This method has been successfully applied to the synthesis of three biologically active molecules.     

Organocatalyst-mediated enantioselective intramolecular Michael addition of aldehydes to vinyl sulfones

Chiral amines with a hydrogen bond donor promote the intramolecular conjugate addition of aldehydes to vinyl sulfones. Chiral cyclic sulfone-aldehydes are obtained in good yields with an ee of up to 82%.     

A straightforward synthesis of cyclobutenones via a tandem Michael addition/cyclization reaction of 2,3-allenoates with organozincs

An efficient method for synthesis of polysubstituted cyclobutenones, which are not readily available from traditional methods due to the intrinsic ring strain, is described. The reaction of 2,3-allenoates and organozinc reagents proceeds via a tandem Michael addition/cyclic 1,2-addition/elimination mechanism with the functional groups from the organozinc reagents being introduced to the 3-position of the cyclobutenone products regiospecifically in moderate to excellent yields. Application to the synthesis of stereodefined β,γ-unsaturated enones is demonstrated.     

Non-catalyzed addition of heterocyclic thiols and 5-substituted-1H-tetrazoles to vinyl ethers

The alkylation of 1-substituted 1H-tetrazole-5-thiols and 4-substituted 4 H-1,2,4-triazole-3-thiols with alkyl halides or sulfonates lead to the formation of S-alkylated products regardless of the substituent on the heterocycle. In this work, we found that substituted 1H-tetrazole-5-thiols and 4 H-1,2,4-triazole-3-thiols readily reacted with vinyl ethers in the absence of a catalyst to exclusively form N-substituted 1H-tetrazole-5(4H)-thiones and 1H-1,2,4-triazole-5(4H)-thiones, respectively. Furthermore, the reactions of 5-substituted-1H-tetrazoles with vinyl ethers under the same conditions selectively yielded 2,5-disubstitued tetrazoles.     

Vinyl sulfone- and vinyl sulfoxide-modified tetrahydrofurans: a preliminary account of the enantiomeric synthesis of and diastereoselectivity of addition to new classes of Michael acceptors

Enantiomerically pure 2-hydroxymethylene substituted-2,5-dihydro-3-(arylsulfonyl)- and 2-hydroxymethylene substituted-2,5-dihydro-3-(arylsulfinyl)-furans have been prepared from easily accessible carbohydrate derivatives for the first time. The strategy for accessing both these sulfones and sulfoxides is more efficient than the methods reported so far for the synthesis of this type of compounds. Hydroxymethylene group is sufficient to impose diastereoselectivity on the addition of a wide range of nucleophiles to vinyl sulfone-modified tetrahydrofurans. The benzyl protected hydroxymethylene group also suppresses the influence of chirally pure sulfoxides as two diastereomeric vinyl sulfoxide-modified tetrahydrofurans afforded the Michael adducts with same configurations at C-3 and C-4; this has been established by oxidizing the adducts, which were found to be identical to the products obtained by adding the same nucleophiles to the corresponding vinyl sulfones. These highly reactive Michael acceptors may be considered as a new addition to the arsenals of synthetic chemists interested in the functionalization of tetrahydrofurans.     

A new reactivity pattern for vinyl bromides: cine-substitution via palladium catalysed C-N coupling/Michael addition reactions

Palladium catalysed C-N bond formation can be used to convert vinyl bromides to the corresponding enamines, which are reacted in situ with alkylidene malonates to provide Michael adducts. The overall transformation results in cine-substitution of the starting vinyl bromide.     

Synthesis of carbo- and heterocycles via a palladium-catalysed allene insertion-nucleophile incorporation-Michael addition cascade

A novel palladium catalysed three-component cascade process is described involving allenylation of an aryl iodide to generate a (π-allyl)palladium species which is intercepted by a carbon or nitrogen nucleophile followed by intramolecular Michael addition to afford carbo- and heterocycles in good yield.     

Synthesis of heterocyclic compounds via Michael and Hantzsch reactions

Heterocycles represent the largest diversity of organic compounds with signifcant chemical, biomedical, and industrial applications. They exist in numerous natural products, dyes, and as scaffolds in diverse drugs and related pharmaceutically active substances. Substantial attention has been paid to develop various elegant methods to synthesize heterocycles. Among different strategies, Michael and Hantzsch reactions are considered as effective approaches for construction of heterocycles and their corresponding fused derivatives. This review covers this area especially in the last 10 years. The heterocyclic systems reported in this review are classified according to the kind of the heterocyclic systems.     

N719 dye-sensitized organophotocatalysis: enantioselective tandem Michael addition/oxyamination of aldehydes

A remarkably efficient photosensitizer, N719 dye, was used in asymmetric tandem Michael addition/oxyamination of aldehydes, rendering α,β-substituted aldehydes in good yields with excellent levels of enantioselectivity and diastereoselectivity. This is the first report of a multiorganocatalytic reaction involving iminium catalysis and photoinduced singly occupied molecular orbital (SOMO) catalysis. This reaction is expected to expand the scope of tandem organocatalytic reactions.     

Synthesis of carbo- and heterocycles via palladium catalysed cascade allene insertion-nucleophile incorporation-Michael addition processes

Novel palladium catalysed two- and three-component thermal (conventional heating and microwave) cascade processes are described involving allenylation of an aryl iodide to generate a (π-allyl)palladium species, which are intercepted (inter- or intramolecularly) by a carbon or nitrogen nucleophile followed by intramolecular Michael addition to afford carbo- and heterocycles in good yields.     

Regioselective tandem dimethylsulfonium methylide addition-eliminative olefination of diendioates: a novel route to 1,3-butadien-2-ylmalonates

The appropriate choice of dimethylsulfonium methylide generation conditions enables the highly regioselective tandem ylide addition-eliminative olefination to 1,3-dienedioates providing 1,3-butadien-2-ylmalonates, a novel class of 2-substituted 1,3-dienes suitable for quick assembly of precursors for type 2 intramolecular Diels-Alder reactions.     

Total synthesis of (-)-kainic acid via intramolecular Michael addition: a second-generation route

A total synthesis of (-)-kainic acid starting from the commercially available 2-azetidinone is described. The key delta-lactone intermediate was concisely prepared from the commercially available azetidinone through the Reformatsky-type reaction and an introduction of a glycine moiety. The construction of the functionalized pyrrolidine ring was executed by a one-pot sequential elimination-Michael addition protocol of a beta-amino-delta-lactone intermediate with high diastereoselectivity.