Cross-aldol reactions of levoglucosenone and its derivatives with cyclohex-1-en-1-ol ethers

The reaction of levoglucosenone with cyclohex-1-en-1-yl trimethylsilyl ether under Mukaiyama reaction conditions gave [1 + 2]-Michael–aldol condensation product with participation of the acetal center. The reaction was accompanied by opening of the 1,6-anhydro bridge and intramolecular hemiketalization by the hydroxy group of the 2-oxocyclohex-1-enyl fragment. Under analogous conditions, dihydrolevoglucosenone gave rise to four diastereoisomeric 1,2-addition products. Internal cyclohex-1-en-1-ol ether obtained by treatment of the Michael adduct of levoglucosenone and cyclohexanone with Ac₂O–ZnCl₂ underwent intramolecular Mukaiyama reaction involving substituted α-carbon atom of the cyclohexanone fragment and acetal moiety to afford spiro derivative and product of subsequent AdE1 acetylation of intermediate α′-cyclohexenyl ether fragment.     

Reaction of levoglucosenone with diazocyclopropane

Depending of the reaction conditions, reaction of levoglucosenone with diazocyclopropane generated in situ from N-cyclopropyl- N-nitrosourea under the action of bases involved either the carbonyl group to give oxaspiropentane (MeONa/MeOH, s-30 °C), or the double C=C bond to give l-pyrazoline (K2CO3, CH2Cl2, 5 °C). The latter readily reacted with diazocyclopropane at the C=O group or added as a C-nucleophile in a regio-and stereoselective Michael reaction to the C=C bond of levoglucosenone. The direction of reaction depended on the reactant ratio. The reaction of the levoglucosenone—diazomethane adduct with an excess of levoglucosenone in the presence of a base yielded similar product bearing two levoglucosenone moieties.     

1,2- and 1,4-addition reactions of cycloalkanones with levoglucosenone

The reactions of levoglucosenone with 2-acetylcyclohexanone and 2-acetyldodecanone occurred as tandem Michael addition and 1: 1 aldol condensation to give the corresponding spiro derivatives. Conditions ensuring 1,2- and 1,4-additions of C_{5–7, 12}-cycloalkanones and enamines derived therefrom to levoglucosenone were found.     

Pyrrolidine and α-methylene-α-lactam from the cyclization of α-(alkylaminoethyl)acrylate: Synthesis of aza-sarkomycins

Diene readily adds primary amines to give which can cyclize either in a Michael addition fashion or via a displacement reaction to give, respectively, pyrrolidine or methylene lactam which further isomerizes to under the employed reaction conditions. Compound can be obtained as the sole product from the reaction of diene precursor with amines followed by vacuum pyrolysis.     

An Intriguing Case of the Retro-Michael Reaction

In the course of Michael addition of carbanions, derived from malononitrile or cyanoacetic ester, to a nitrostyrol retro reaction has also been observed. Depending on the reaction conditions any of the two compounds formed can be obtained as main product. The entire process has been thoroughly investigated.     

Convenient one-pot synthesis of fluorinated DHPs derivatives and their further transformations

One-pot four-component reactions of aromatic aldehyde, Meldrum’s acid, ethyl-4,4,4-trifluoro-1,3-dioxobutanoate, and ammonium acetate afford ethyl 2-hydroxy-6-oxo-4-aryl-2-(trifluoromethyl)piperidine-3-carboxylate in good yields. The one-pot four-component process consists of an initial Michael addition, and a subsequent intramolecular cyclization. The effect of solvents on the reaction efficiency and yield is briefly investigated. The structure of product is further confirmed by XRD analysis. Meanwhile, the further transformation of hemi-aminal moiety to the corresponding dehydrated product is also achieved under the mild reaction conditions. The possible mechanism for the formation of product is presented.     

Threo selective cross aldol condensation with thioamide enolates generated by a michael addition of organometallics to unsaturated thioamides

Crotonothioamide, sorbothioamide, and cinnamothioamide undergo a threo selective aldol condensation via their enolates generated by a Michael addition of organometallics.     

Addition reactions of thiazol-5(4H)-ones—II : Cycloaddition and Michael addition reactions of 4-substituted 2-phenylthiazol-5(4H)-ones

The mixture of adducts formed under mild conditions between a 4-substituted 2-phenylthiazol-5(4H)-one and an electron-deficient alkene is shown to include a stable cycloadduct and a Michael adduct formed through the 2- or the 4-position of the thiazolone. The reaction can be diverted towards the Michael adduct entirely, by adding traces of aqueous alkali to the reactants in acetone solution. A novel type of 1:2-adduct is present in the reaction mixture, and is shown to be formed through reaction of the cycloadduct with the alkene. A product formed by extrusion of carbonyl sulphide from the cycloadduct is the same as that obtained from the analogous oxazolone and the alkene, but generally the differences between the propensity of oxazolones and thiazolones to undergo various types of addition reaction with representative dipolarophiles are shown to be substantial.     

Reaction of the levoglucosenone Diels–Alder adducts with acetaldehyde under the McMurry conditions

Reactions of acetaldehyde with Diels–Alder adducts of levoglucosenone with butadiene, isoprene, and cyclohexa-diene assisted by low-valence titanium afford products of acetaldehyde addition to the acetal center with opening of the 1,6-anhydro bridge. In the case of the cyclopentadiene adduct, the reaction gives the product of addition of the ethyl substituent to the acetal center while the 1,6-anhydro bridge remains unchanged.     

Eleuthesides and their analogs: V. Medium- and large-ring lactones based on levoglucosenone

Ozonolysis of the bridging double bond in bicyclic enol ethers obtained by the Michael reaction and subsequent intramolecular etherification afforded chiral decanolides fused to a tetrahydropyran ring. Three-step procedures were developed for the synthesis of chiral lactones with medium and large rings via oxidative cleavage with pyridinium chlorochromate of mixed bicyclic ketals which were prepared by treatment with methanolic HCl of Michael adducts derived from levoglucosenone and cyclopenta-, cyclohexa-, cyclohepta-, and cyclododecanone.     

Thiosugars Iii. Stereoselective Approach to β-(1→2)-2,3-Dideoxy-2-C-Acetamidomethyl-2-S-Thiodisaccharides From Levoglucosenone

ABSTRACT

β-(1→2)-2,3-Dideoxy-2-C-acetamidomethyl-2-S-thiodisaccharides were synthesized in four steps by a stereoselective base catalyzed Michael addition reaction of 1-thiosugars to α-nitroalkene 4a, a new chiral synthon from levoglucosenone. It was followed by the reduction of the nitro group with a sodium borohydride/cobalt chloride complex and the hydrolytic opening of the 1,6-anhydro ring.     

Reaction of nitroalkanes with levoglucosenone and its α-bromo and α-iodo derivatives. Cyclopentaannulation of α-halocyclenones

Michael reactions of levoglucosenone and its α-bromo and α-iodo derivatives with α,ω-dinitroalkanes were studied under conditions of chemical and electrochemical generation of base. Procedures were developed for stereospecific fusion of a cyclopentane ring to α-bromo- and α-iodolevoglucosenones, 2-iodocyclopent-2-en-1-one, and 2-iodocyclohex-2-en-1-one by the action of 2,2-dimethyl-1,3-dinitropropane.     

Catalytic Diastereoselective Tandem Conjugate Addition–Elimination Reaction of Morita–Baylis–Hillman C Adducts by C?C Bond Cleavage

Through the cleavage of the C? C bond, the first catalytic tandem conjugate addition–elimination reaction of Morita–Baylis–Hillman C adducts has been presented. Various S_N2′‐like C‐, S‐, and P‐allylic compounds could be obtained with exclusive E configuration in good to excellent yields. The Michael product could also be easily prepared by tuning the β‐C‐substituent group of the α‐methylene ester under the same reaction conditions. Calculated relative energies of various transition states by DFT methods strongly support the observed chemoselectivity and diastereoselectivity.     

Michael addition reactions for the modification of gold nanoparticles facilitated by hyperbaric conditions

The chemical interfacial modification of organic solvent soluble 2.4 ± 0.5 nm maleimide-modified monolayer protected gold nanoparticles (2-C(12)AuNPs) with primary or secondary amines via Michael addition reactions is demonstrated. Michael addition reactions between 2-C(12)AuNPs and primary or secondary amines at ambient temperature and pressure and under the conditions where the AuNP is soluble and stable are possible albeit sluggish, often taking days to weeks to go to completion. The rates and efficacies of the these same reactions are drastically increased at hyperbaric pressure conditions (11?000 atm) with no observed adverse effect to the gold nanoparticle stability. The resulting Michael addition adducts (3-C(12)AuNPs) formed from 2-C(12)AuNPs and the corresponding amines were characterized by TEM and by comparison of the (1)H NMR spectra of the 3-C(12)AuNPs with those of model reactions of the same amines with N-dodecylmaleimide, 2. The Michael addition reactions occur more readily with 2 rather than 2-C(12)AuNPs, consistent with the local environment of the latter imposing additional steric or other barriers to the reaction. The use of hyperbaric conditions makes the reaction of the organic solvent soluble 2-C(12)AuNP via Michael addition a viable interfacial modification process that is otherwise impractical. The results also suggest that it is a useful protocol for facilitating Michael addition reactions generally in solution at low temperatures.     

Polymer-incarcerated gold-palladium nanoclusters with boron on carbon: a mild and efficient catalyst for the sequential aerobic oxidation-Michael addition of 1,3-dicarbonyl compounds to allylic alcohols

We have developed a polymer-incarcerated bimetallic Au-Pd nanocluster and boron as a catalyst for the sequential oxidation-addition reaction of 1,3-dicarbonyl compounds with allylic alcohols. The desired tandem reaction products were obtained in good to excellent yields under mild conditions with broad substrate scope. In the course of our studies, we discovered that the excess reducing agent, sodium borohydride, reacts with the polymer backbone to generate an immobilized tetravalent boron catalyst for the Michael reaction. In addition, we found bimetallic Au-Pd nanoclusters to be particularly effective for the aerobic oxidation of allylic alcohols under base- and water-free conditions. The ability to conduct the reaction under relatively neutral and anhydrous conditions proved to be key in maintaining good catalyst activity during recovery and reuse of the catalyst. Structural characterization (STEM, EDS, SEM, and N(2) absorption/desorption isotherm) of the newly prepared PI/CB-Au/Pd/B was performed and compared to PI/CB-Au/Pd. We found that while boron was important for the Michael addition reaction, it was found to alter the structural profile of the polymer-carbon black composite material to negatively affect the allylic oxidation reaction.     

A Convenient Procedure for the Synthesis of 4,6-Disubstituted 2-OXO-2H-Pyran-5-carboxylic Esters.

A simple procedure for the synthesis of 2H-pyran-2-ones 2a is described: The initial Michael addition product of β-ketoester anions with acetylenic esters readily cyclizes under the basic reaction conditions to give the α-pyrones 2a (Scheme 2).     

Michael addition of indoles to β-nitrostyrenes catalyzed by HY zeolite under solvent-free conditions

Michael addition of indoles to β-nitrostyrenes is reported using HY zeolite as catalyst under mild reaction conditions. This methodology allows the synthesis of various indole derivatives in good to high yields at 50 °C under solvent-free conditions. The short reaction time and achieving high yield of the desired products are the main advantages of the present work. The catalyst can be easily recovered and reused for six successive runs without considerable changes in yields. This Michael addition catalyzed by HY zeolite is operationally simple and can be considered as a greener protocol as it avoids the use of corrosive acids and toxic reagents.     

Sodium tetramethoxyborate: an efficient catalyst for Michael additions of stabilized carbon nucleophiles

Sodium tetramethoxyborate, easily prepared by reaction of inexpensive sodium borohydride with methanol, possesses a suitable combination of a Lewis base and a Lewis acid to catalyze Michael reactions at room temperature under practically neutral conditions. This reaction provides good to excellent yields of Michael addition products from a broad scope of Michael donor and Michael acceptor reagents.     

Synthesis of highly functionalized indeno[1,2-b]furans

Some novel functionalized indeno[1,2-b]furans were synthesized from the reaction of indandione/indanone and aldehydes at room temperature followed by the reaction of the Knoevenagel condendensed intermediate with 4-hydroxycoumarins in the presence of iodine as catalyst in dimethyl sulfoxide (DMSO) under thermal conditions. The reaction involved in a condensation and Michael addition followed by lactone ring opening and intramolecular cyclization process to afford the product in high yield in easy work-up procedure.     

STERIC CONTROL OF THE P-CHIRAL GROUP IN GRIGNARD ADDITION TO THE CARBONYL GROUP OF α - KETOPHOSPHINE OXIDE

Abstract

1,2-Asymmetric inductions in Grignard addition to the carbonyl group of α-keto P-chiral phosphine oxides have been investigated. The favoured reaction product erythro-, 6, is thermodynamically less stable than the threo isomer. This seems to be the first stereochemical evidence of the reversible character of reaction addition of sec-phosphine oxides to the carbonyl group.