Michael microwave assisted

Scheme 27 Microwave-assisted Knoevenagel condensation and Michael addition cascade...

Ranu, B.C., Guchhait, S.K., Gosh, K. and Patre, A., Construction of bicyclo[2.2.2]octanone systems by microwave-assisted solid phase Michael addition followed by AI2O3-mediated intramolecular aldolisation. 

Steroidal, alicyclic or aromatic annulated pyridines were prepared via a microwave-assisted, base-catalyzed Henry reaction of /1-formyl enamides and nitromethane on an alumina support [97]. Highly substituted tri- and tetrasubstituted pyridines were synthesized in a Bohlmann-Rahtz reaction from ethyl /3-amino crotonate and various alkynones. The reaction involved a Michael addition-cyclodehydration sequence and was effected in a single synthetic step under microwave heating conditions [98]. An alternative approach towards polysubstituted pyridines was based on a reaction sequence involving an inverse electron-demand Diels-Alder reaction between various enamines 45 and 1,2,4-triazines 44 (Sect. 3.6), followed by loss of nitrogen and subsequent elimination-aromatization. Enamines 45 were formed in situ from various ketones and piperidine under one-pot microwave dielectric heating conditions [99]. Furthermore, a remarkable acceleration of the reaction speed (from hours and days to minutes) was observed in a microwave-assisted cycloaddition. Unsymmetrically substituted enamines 45 afforded mixtures of regioisomers (Scheme 35). 

FriedelCrafts reactions are almost unknown in pyridine and azine chemistry. Direct electrophilic alkylation at the pyrimidine 5-position can be carried out on pyrimidines which have at least two strongly donating groups, and more readily with three such groups. Thus, -haloketones and -bromocarboxylic esters can be used for direct alkylation of 6-aminouracils 131, for example, in the formation of 132. The 5-position can also act as the nucleophile for Michael additions (e.g., 131 133) <1992AHC(55)129>. A microwave-assisted procedure allows formation of 5-hydroxymethy-luracil 135 from 134 in 98% yield, in just 3 min <2002SL2043>. Barbituric acids also add to Michael acceptors < 1985AHC(38)229>. 

Ranu, B.C., Saha, M., and Bha, S. 1997. Microwave assisted Michael addition of cycloaUc-enones and substituted enones on the surface of alumina in dry media. Synthetic... 

Polshettiwar V, Varma RS (2010) Nano-organocatalyst magnetically retrievable ferrite-anchored glutathione for microwave-assisted Paal-Knorr reaction, aza-Michael addition, and pyrazole synthesis. Tetrahedron 66 1091-1097... 

Fustero, S., Jimenez, D., Sanchez-Rosello, M. and del Pozo, C. (2007) Microwave-assisted tandem cross metathesis intramolecular aza-Michael reaction an easy entry to cyclic P-amino carbonyl derivatives. J. Am. Chem. Soc., 129, 6700-6701. 

Zare A, Hasaninejad A, Zare ARM, Parhami A, Sharghi H, Khalafi-Nezhad A (2007) Zinc oxide as a new, highly efficient, green, and reusable catalyst for microwave-assisted Michael addition of sulfonamides to a,P-unsaturated esters in ionic liquids. Can J Chem 85 438-444... 

Sviridove et al. [75] proposed microwave-assisted Michael addition in the presence of AI2O3 (Scheme 11.22). o-Alkylation under microwave irradiation is reported by Majidoule et al. [76] (Scheme 11.23). The reaction was carried out in the presence of KOH and the yield of product was 74-94%. 

Michael D., Mingos P. (2005) Theoretical aspects of microwave dielectric heating. Microwave Assisted Organic S3mthesis. Tierney J., P., Lidstroem P. editors. Blackwell Publishing Ltd. pp. 63-179. 

The efficient solvent-free microwave-assisted procedure for C-alkyl pyrroles synthesis using silica gel-supported reagent has been reported. Thus, a general procedure for the Michael addition of pyrroles with electron-deficient olefin has been developed. In the case of the moderately bulky electron-deficient olefins, a catalytic amount of BiCls has to be employed to promote the reaction. The experimental results indicated that BiCla exhibited a high catalytic activity and did not induce polymerization and polyalkylation under microwave (Equation 5) [26a]. 

E. Balint, J. Takacs, L. Drahos, G. Keglevich, Microwave-assisted phospha-Michael addition of dialkyl phosphites, a phenyl-H-phosphinate, and diphenylphosphine oxide to maleic derivatives. Heteroatom Chem. 23 (2012) 235-240. 

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