Dehydration, formation microwaves

An improved synthesis of the Cn-terpenic lactone Dihydroactinidiolide was described by A.K. Bose et al. [35]. The synthesis started from a commercially available aldehyde that was subjected to treatment with m-CPBA and a catalytic amount of PTSA (Scheme 10). The intermediate epoxy acid underwent cyclization resulting in the formation of Aeginetolide. Dehydration has been reported earlier by heating of this compound with aqueous NaOH, at 60 °C for 24 h, or with SOCI2 and pyridine at room temperature for 5 h. The authors observed expeditious and convenient dehydration of this compound supported on silica gel, under microwave irradiation for 5 -10 min (domestic oven), yielding Dihydroactinidiolide in 80% yield. 

Resin-bound nitroalkenes were synthesized via a Knoevenagel condensation of resin-bound nitro acetic acid with aryl and alkyl substituted aldehyde (Scheme 9.29). In this way an extra site of diversity can be introduced into the cycloaddition products of these nitroalkenes. Furthermore, the resin-bound nitroalkenes can serve as activated alkenes in other cycloaddition reactions (Diels-Alder, 1,3-dipolar cycloaddition, [2 + 2] cycloaddition) and therefore lead to the solid phase synthesis of other interesting compoimd classes (see also Scheme 9.3, Sect. 9.2). Formation of the resin-bound nitroalkenes 73a-e was realized in one step via a microwave-assisted condensation of aldehyde 72a-e (10 equiv.) with the resin-bound nitro acetic acid 71, followed by dehydration of the intermediate y -nitroalcohol [6] (Scheme 9.29). THF was used as the solvent in order to obtain optimal diffusion of the aldehyde in the polystyrene resin. 

Wipf et al. (2005) reported microwave irradiated rapid 0,N-acylation-cyclo-dehydration cascade reaction of oximes and acid chlorides to give oxazoles. The microwave irradiation allowed considerable acceleration of the rate of oxazole formation and increased the yield of this synthetically attractive heterocycle formation process. The starting oximes were readily obtained from commercially available ketones in yields exceeding 90%, while the yields of isolated oxazoles ranged from 23% to 62%. 

Sheinburg et al have explored several evaporative approaches to powder formation from aqueous nitrate solutions in the Gd-Ba-Cu-0 system including microwave drying and decomposition. Simple microwave dehydration of the nitrate solutions yielded fine powders, with continued heating causing some decomposition (though not the Ba(N03)2). The principle problems with... 

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