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psyloxy (Hive Addict) 09-26-03 05:26 No 461187 |
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2,5-diMeO-benzaldehyde,an unusual synth from 14DMB (Rated as: excellent) |
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1,4-diMeO-benzene is first nitromethylated with Mn(Ac)3 followed by a Nef reaction to get the benzaldehyde. Overall yield should be in the 50% area. Aromatic Nitroalkylation promoted by Mn(Ac)3. General Procedure[1]. Mn(Ac)3 (10mmol), aromatic hydrocarbon (10ml), MeNO2 (25ml) and AcOH (25ml) were refluxed together under N2 atmosphere with continuous stirring until the brown Mn(Ac)3 was reduced to white Mn(Ac)2. After cooling, the rxn mixtr. was poured onto Et2O (25ml) and water (50ml). The resulting organic layer was separated, washed with dH2O, 5% aqu. Na2CO3, dried and concentrated for subsequent analysis by GC. The same procedure was also used for reactions involving additional reagents (e.g., NH4NO3,KOAc, KBr, Ac2O,H2O). Nitromethylation product from p-diMeO-benzene was isolated by column chromatography (silica gel, mixed CHCl3-hexanes as mobile phase). Yield for 2(Nitromethyl)-1,4-dimethoxybenzene was 71%. Use of EtNO2 is useless as it gives terrible yields of the wrong isomere. As an article directly following the one reviewed by me, shows Cerium saltse can also be used to promote nitromethylation, but that was only tested on benzene/toluene - results were by no means discouraging. It's a pity I only have the first page of that article. Carbonyl Compounds from Nitroalkanes. General Procedure[2]: To a stirred solution of the corresponding nitro compound (10mmol) in MeOH (50ml), cooled to 0°C, is added 30% H2O2 (20ml), followed by a solution of K2CO3 (8g) in dH2O (25ml). The stirring is continued for 8h at room temp . The solution is then acidified with dilute HCl (50ml) and extracted with DCM (3x20ml).The combined organic layers are dried with anh. Na2SO4 and the solvent is removed under red. pressure to give almost pure carbonyl compound. Products are further purified by distillation or recrystallisation. Yield of benzaldehyde from phenylnitromethane was 78%. [1]Kurz, Michael E.; Ngoviwatchai, Preecha; Tantrarant, Tosaporn; JOCEAH; J.Org.Chem.; EN; 46; 23; 1981; 4668-4672 [2]Olah, George A.; Arvanaghi, Massoud; Vankar, Yashwant D.; Prakash, G.K.Surya; SYNTBF; Synthesis; EN; 8; 1980; 662-663 --psyloxy-- |
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Rhodium (Chief Bee) 09-26-03 07:54 No 461204 |
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Good idea! Here are some related links from my page: Reference 2: George A. Olah et. al., Synthesis 662-663 (1980) (../rhodium /nef.pe Preparation of Manganese(III)Acetate (../rhodium /mangan |
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