Michael adduct microwave

Acetylacetone la (10 mmol), metliyl vinyl ketone 2a (10 mmol) and bismuth trichloride (0.32 g, 10% mol) were mixed together without solvent in an Erlen-meyer flask and placed in a commercial microwave oven (operating at 2450 MHz frequency) and irradiated for 15 min. The reaction mixture was allowed to reach room temperature and extracted with chloroform. Removal of solvent and the residue on purification by passing through a short column of silica gel using chloroform as eluent, affords the Michael adduct 4a in 90% yield without tlie formation of any side products. Similarly cadmium iodide (10% mol) was used in place of bismuth trichloride and the corresponding Michael adduct was isolated in 85% yields. 

The reactions of esters of ,/i-unsatu rated acids with a 1.5 fold excess of amines were carried out without a solvent in a commercial microwave oven (Funai M0785VT) in a reaction vessel for several minutes. The power of microwave irradiation depends on the stability of the starting compound under microwave irradiation conditions. The Michael adduct was separated from the unreacted starting substances by column chromatography on silica gel with a hexane-ethyl acetate mixture (2 1) as the eluent. 

An expeditious and highly diastereoselective synthesis of (Z)-2-alkylsulfenyl (or 2-cyano) -2,4-diarylthietanes 53 has been reported by nucleophile (CN, RS") induced cyclization of the corresponding O,O-diethyl 5-(l,3-diaryl-3-oxopropyl) phosphorodithionates under microwave irradiation in solvent free conditions <02S1502>. This reductive cyclization can be considered to be induced by the attack of a hydride ion on the carbonyl carbon of the Michael adduct precursor to give an alkoxide ion, which attacks the phosphorus atom intramolecularly. 

An attempt to use 2-hydroxybenzaldehyde for the DABCO-catalyzed reaction with methyl acrylate in chloroform led to diadduct 103 in 10% yield this product is also obtained on microwave irradiation in a shorter time and with higher yield." However, on using methylene chloride instead of chloroform as the solvent, quaternary salt 104 was isolated, which for the first time proved that the elusive Michael adduct, postulated by all researchers in the area, did exist the counterion chloride is presumably derived from the solvent (Scheme 1.50). "... 

Porco and co-workers used a diversity oriented/ring-closing metathesis approach to construct several complex systems as small molecule protein modulators.Microwave irradiation of Michael adduct 323 in the presence of a catalytic amount of 4 in refluxing dichloromethane gave the corresponding cyclooctene derivative 324 in modest yield. The authors included several additional examples as part of their report. 

A new thiophen synthesis is based on deprotonation and cyclization of the resultant carbanion (65) of a keten dimethylthioacetal. Other applications of cr-(phenylthio)- or cr-(alkylthio)-alkyl-lithiums include preparations of disparlure (the sex pheromone of the gypsy moth) and other chiral epoxides,of an anti-peptic-ulcer diterpene from Croton sublyratus, of carbene-thiometal chelates through reaction with fCr(CO)gl or fW(CO)jl, of olefins via )ff-hydroxy-sulphides, and of Michael adducts of enones. In other work, the chiral solvent l,4-dimethylamino-2,3-dimethoxybutane is employed in enantioselective addition reactions of cr-thio-carbanions with ketones and Michael acceptors. a,P -Elimination of cr-thio-carbanions such as (66) provides a useful synthesis of olefins, and a 2-(lithiomethylthio)-A -oxazoline (67) has been used to prepare a C-labelled thiiran for a microwave study of the valence tautomerism of allene episulphide. ... 

Another Michael-type addition followed by cyclization and dehydration was also reported by Ranu et af, but in a diff erent system [217]. Aryl amines were reacted with a,p-unsaturated ketones to form Michael adducts, and the resulting intermediates proceeded to cyclize, forming quinolines (Figure 8.98). The reaction was catalyzed by InCls impregnated silica gel, using microwave irradiation. The pathway was confirmed through isolation of the Michael product and subsequent reaction of this intermediate. Note that p-disubstituted alkyl vinyl ketone gave dihydroquinolines instead [218]. 

It was observed that the microwave activation of the Michael addition between chiral a-alkoxy imine and methyl acrylate at 100 °C resulted into the corresponding Michael adduct with better yield compared to thermal rearrangement (Camara et al., 2003). The product has same regio- and stereoselectivity. 

A series of Michael adducts has been synthesized with high yields by solvent-free microwave promoted Michael addition of aza-nucleophiles to benzo[b]thiophen-2-yl-2-propenone (Pessoa-Mahana et al., 2009). In this method, aliphatic and aromatic amines act as Michael donors and on treatment with l-(4,7-dimetho2 benzo[b] thiophen-2-yl)-2-propen-l-one led to formation of P-aminoketones and azahetero-cyclic compounds. These aza-nucleophiles were impregnated on silica gel-manganese dioxide as solid inorganic support. 

A mixture of 1,3-dicarbonyl compound 1 (2 mmol), Michael acceptor 2 (2.4 mmol) and Eu3+ catalyst is submitted to microwave irradiation in a kitchen oven under the conditions reported in the Table. Then the crude mixture is directly poured onto the top of silica gel chromatographic column and elution with petroleum ether-ethyl acetate mixtures affords pure adducts 3. 

Narsaiah and Krishnaiah (2002) reported that the hetero-Diels-Alder reaction of A(-acetyl perflnoroalkyl substituted 2(1//) pyridones with DMAD on neutral alumina under solvent-free microwave irradiation conditions extended to undergo an inverse electron demand hetero-Diels-Alder reaction, resulting exclusively in E, Z isomers (3 1) of Michael-type A-adducts. 

Condensations. Alumina promotes the formation of a-hydroxyphosphonate esters from aromatic aldehydes and dialkyl phosphonates, and the adducts are converted to a-aminophosphonate esters on reaction with ammonia. A solvent-free synthesis of a-nitro ketones comprises mixing nitroalkanes, aldehydes, and neutral alumina and oxidizing the adducts with wet, alumina-supported CrOj (15 examples, 68-86%). The Knoevenagel reaction, the Michael addition of nitromethane to gcm-diactivated alkenes, and the formation of iminothiazolines from thioureas and a-halo ketones are readily effected with alumina under microwave irradiation. 

Michael additions of /3-diketones to a-, /3-unsaturated ketones can be run without solvent with the help of microwave radiation (8.5) to give the adducts in 63-95% yields.49 Cerium(III) chloride can also be used. No polymerization of the methyl vinyl ketone takes place. 

An interesting example is the solvent-free Michael addition reaction of nitromethane to chalcone in the presence of alumina under microwave irradiation condition that gives the adduct in 90% yield (Scheme 91). ... 

---