Solvent-free organic syntheses. using supported reagents and microwave irradiation
Recent developments in microwave-accelerated solventless organic syntheses are summarised. This expeditious and solvent-free approach involves the exposure of neat reactants to microwave (MW) irradiation in conjunction with the use of supported reagents or catalysts which are primarily of mineral origin. The salient features of these high yield protocols are the enhanced reaction rates, greater selectivity and the experimental ease of manipulation. Among other reagents recently described in the literature on this eco-friendly green approach, the use of recyclable mineral oxides or supported reagents from our laboratory such as Fe(NO3)3–clay (clayfen), Cu(NO3)2–clay (claycop), NH4NO3–clay (clayan), NH2OH–clay, PhI(OAc)2–alumina, NaIO4–silica, CrO3–alumina, MnO2–silica, NaBH4–clay, etc. are highlighted in MW-promoted deprotection, condensation, cyclization, rearrangement, oxidation and reduction reactions including the rapid one-pot assembly of heterocyclic compounds from in situ generated intermediates.