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Dehydration
Dehydration reactions also work exceptionally well with microwave irradiation. Simple dehydrations of alcohols to carbon–carbon double bonds639-642, cyclodehydration reactions643,644, and aldehydes to nitriles93,645-651 can all be successfully executed in 1-15 minutes. Scheme 119 exhibits the dehydration of parthenin to anhydroparthenin.639 Flavones can be synthesized from o-hydroxydibenzoylmethanes on clay by cyclodehydration (Scheme 120).644
Scheme 119
Aldehydes on bentonite clay can be converted to nitriles by using hydroxylamine hydrochloride and microwave irradiation (Scheme 121).651
Scheme 120
Scheme 121
Instruments
93. Varma, R.S.; Naicker, K.P. “Hydroxylamine on clay: a direct synthesis of nitriles from aromatic aldehydes using microwaves under solvent-free conditions.” Molecules Online 1998, 2, pp. 94-96.
639. Das, B.; Venkataiah, B.; Kashinatham, A. “Chemical and biochemical modifications of parthenin.” Tetrahedron 1999, 55, pp. 6585-94.
640. Subbaraju, G.V.; Manhas, M.S.; Bose, A.K. “Studies on terpenoids. An improved synthesis of (-)-dihydroactinidiolide.” Tetrahedron Lett. 1991, 32, pp. 4871-74.
641. Das, B.; Venkataiah, B. “Synthetic studies on natural products. 7. Conversion of parthenin to anhydroparthenin using microwave irradiation.” Synth. Commun. 1999, 29, pp. 863-66.
642. Jayaraman, M.; Batista, M.T.; Manhas, M.S.; Bose, A.K. “Studies of lactams. 106. Organic reactions in water: indium mediated synthesis of α-alkylidene-β-lactams.” Heterocycles 1998, 49, pp. 97-100.
643. Meshram, H.M.; Sekhar, K.C.; Ganesh, Y.S.S.; Yadav, J.S. “Microwave thermolysis. XI. Clay catalyzed facile cyclodehydration under microwave: synthesis of 3-substituted benzofurans.” Synlett. 2000, pp. 1273-74.
644. Varma, R.S.; Saini, R.K.; Kumar, D. “An expeditious synthesis of flavones on Montmorillonite K-10 clay with microwaves.” J. Chem. Res. (S) 1998, pp. 348-49.
645. Kumar, H.M.S.; Mohanty, P.K.; Kumar, M.S.; Yadav, J.S. “Microwave promoted rapid dehydration of aldoximes to nitriles on a solid support.” Synth. Commun. 1997, 27, pp. 1327-33.
646. Sabitha, G.; Syamala, M. “Microwave induced conversion of aldozimes to nitriles by DBU.” Synth. Commun. 1998, 28, pp. 4577-80.
647. Das, B.; Madhusudhan, P.; Venkataiah, B. “Studies on novel synthetic methodologies. Part 4. An efficient microwave-assisted one-pot conversion of aldehydes into nitriles using silica gel-supported NaHSO4 catalyst.” Synlett. 1999, 10, pp. 1569-70.
648. Bose, D.S.; Narsaiah, A.V. “Efficient one-pot synthesis of nitriles from aldehydes in solid state using peroxymono-sulfate on alumina.” Tetrahedron Lett. 1998, 39, pp. 6533-34.
649. Chakraborti, A.K.; Kaur, G. “One-pot synthesis of nitriles from aldehydes under microwave irradiation: influence of the medium and mode of microwave irradiation on product formation.” Tetrahedron 1999, 55, pp. 13265-268.
650. Feng, J.C.; Liu, B.; Bian, N.S. “One-step conversion of aldehydes into nitriles in dry media under microwave irradiation.” Synth. Commun. 1998, 28, pp. 3765-68.
651. Delgado, F.; Cano, A.C.; Garcia, O.; Alvarado, J.; Velasco, L.; Alvarez, C.; Rudler, H. “A direct synthesis of aromatic nitriles from aldehydes using a Mexican bentonite and microwave or infrared irradiation, in absence of solvent.” Synth. Commun. 1992, 22, pp. 2125-28.