Nitromethane, adduct formation with

In the Mukaiyama aldol additions of trimethyl-(l-phenyl-propenyloxy)-silane to give benzaldehyde and cinnamaldehyde catalyzed by 7 mol% supported scandium catalyst, a 1 1 mixture of diastereomers was obtained. Again, the dendritic catalyst could be recycled easily without any loss in performance. The scandium cross-linked dendritic material appeared to be an efficient catalyst for the Diels-Alder reaction between methyl vinyl ketone and cyclopentadiene. The Diels-Alder adduct was formed in dichloromethane at 0°C in 79% yield with an endo/exo ratio of 85 15. The material was also used as a Friedel-Crafts acylation catalyst (contain-ing7mol% scandium) for the formation of / -methoxyacetophenone (in a 73% yield) from anisole, acetic acid anhydride, and lithium perchlorate at 50°C in nitromethane. 

Electrochemical oxidation of 2,3,4,5-tetraphenylpyrrole in aqueous media yields 3,3,4,5-tetraphenylpyrrolin-2-one, whereas when the oxidation is conducted in nitromethane, nucleophilic attack by the nitromethyl anion and subsequent rearrangement of the adduct with the extrusion of the nitrite ion lead to the formation of 2,3,4,6-tetraphenylpyridine (B-77MI30507, 81H(15)495>. 

For monocyclic pyrylium salts, the realization of an alternative pathway is equally possible [82ACH(Suppl)]. But for 2-benzopyrylium salts, even in the reaction with nitromethane, which is able to act only as a 1,1-nucleophile, the formation of naphthalene 228 was not more than 5%, whereas adduct 227 was isolated quantitatively (90KGS315). 

Equation 26. Electron-deficient flavins will also oxidize nitroalkane anions in model reactions (12). The observation (11) that nitromethane anion and FloXEt yield a stable 4a-adduct is evidence that 4a-adducts are not on the reaction path for nitroalkane oxidation. That the blocking of the N(5)-position of flavin (i.e., FloxEt) prevents oxidation of nitromethane would, however, be in accord with the requirement for an N(5)-adduct (11). The nitroalkane reaction with flavoenzyme has been used to implicate N(5)-adducts as intermediates in the oxidation mechanism of amino acid oxidases. However, it must be understood that nitroalkane anions differ significantly from the carbanions generated from a normal substrate. The nitroalkane anion on loss of its pair of electrons would provide an impossibly unstable carbonium ion, whereas in the case of the amino acid anion an internal electron release obviates carbonium ion formation. 

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. 

For the formation of 7, a change from the conventional SNAr mechanism (cf. p. 353) to a radical SET process with successive dimerization is likely to be responsible [220], Organolithium compounds and CH-acidic compounds add to acridine at the 9-position to give 9,10-dihydroacridines. For instance, with nitromethane in basic medium, the adduct 8 is formed, whereas phenyhnethylsulfone yields 9-methylacridine, since the adduct 9 eliminates phenylsulfinic acid ... 

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