Author Topic: alkylation of 3-OH vs 4-OH benzaldehydes?  (Read 1870 times)

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hypo

  • Guest
alkylation of 3-OH vs 4-OH benzaldehydes?
« on: August 08, 2002, 05:19:00 AM »
hi,

if we look at the phenolates of 3-OH and 4-OH benzaldehydes, we see
that in the 4-OH case, the phenolate is in resonance with the formyl
group, whereas in the 3-OH case it isn't (if this is not clear, i
can make a quick sketch of what i mean).

1) does that mean that in the 4-OH case the negative charge is more
dislocated and thus the alkylation is _slower_ (maybe not noticeable)
than in the 3-OH case?

2) does that mean that in the 4-OH case, the formyl group can also
be alkylated? giving a strange compound (which i can't name)?

3) now suppose we have a MeO or other activating group in the 5 position.
this would speed up the 4-OH alkylation (two negative charges on the ring),
but would still leave the possibility of the formyl alkylation?

i hope i ain't annoying people with my questions!  :-[

couch terrorist

Rhodium

  • Guest
As far as I know, aldehyde allylation require a ...
« Reply #1 on: August 08, 2002, 08:15:00 AM »
As far as I know, aldehyde allylation require a catalyst like Sm/In/Mg etc...

GC_MS

  • Guest
Alkylation of the formyl
« Reply #2 on: August 08, 2002, 08:59:00 AM »
Alkenylation of the formyl is done a la Perkin.

anisaldehyde + EtCOONa -> H2O + MeO-C6H4-CH=CMeCOONa
MeO-C6H4-CH=CMeCOOH - CO2 = anethole

Old trick from the perfume industry  ;) . No Sm/In etc necessary, though Perkin forms propenyl compounds, and not allyl.
SWiM doesn't have the necessary articles handy to help you much further hypo. Till now, he mainly need DEmethylation reviews  ;)

Doped(TM) since 19.... euhm... a long time  :)

hypo

  • Guest
heh...
« Reply #3 on: August 08, 2002, 09:23:00 AM »
thanks.

rhodium: i see how normal aldehydes are pretty unreactive, but
shouldn't benzaldehyde and especially benzaldehydes with an -O-
in 4 position be pretty reactive?

GC_MS: alk(en)ylation on the formyl group is _not_ what i want. rather my
concern was if, when alkylating a 4-formyl-phenolate, etherification of the
formyl group would be a side reaction. if not, then why not?

this is the compound i'm talking about in the case of alkylation with
propyliodide:













Molecule:

watchamacallit ("O=C1C=CC(=COCCC)C=C1")



couch terrorist