Author Topic: 2,5-diMeO-benzaldehyde,an unusual synth from 14DMB  (Read 1902 times)

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psyloxy

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2,5-diMeO-benzaldehyde,an unusual synth from 14DMB
« on: September 26, 2003, 05:26:00 AM »
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

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Rhodium

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