2
T. CHEIRMAKANI
synthesis of diclofenac, a non-steroidal anti-inflammatory, dicycloxygenase inhibitor,
and as precursors for the benzo-fused coumarins having anti-tumor activity[8].
However, the synthesis of allyl phenyl ethers is always a very challenging task because
of achieving regioselectivity. The traditional methods for the synthesis of allyl ethers
normally require strongly basic metal alkoxide anion, highly active alkyl species, and a
stoichiometric amount of coupling agents such as DEAD and triphenylphosphine[9]. In
addition, to activate the allyl alcohol, either the use of ligands, supporting agent, addi-
tives, or elevated temperatures are also necessary due to its less reactivity. There are
other few reports also available which includes metal complexes like Ru[10], Pd[11]
,
Ir[12], Mo(II)[13], In[14], Au[15], Rh[16] for the allylation of phenolic compounds.
Recently, nanoferrites[17], lead composite[18], PTC[19], cyclodextrins[20] are also reported.
However, most of the reported procedures involve both C- and O-allylation by the use
of expensive ligands for the complex formation, toxic solvents, limited substrate scope,
strong base, harsh reaction conditions, non-recyclable catalyst, and poor selectivity.
Our recent report on allylation of dicarbonyl compounds[21] using hierarchically
architectured MMZCu(I)Y prompted us to extend the study of the allylation of functional
moieties like OH groups as the reported catalytic system can influence the outcome of
product selectivity. Moreover, the catalyst reserves its own advantages like functional
tolerance, tunable acidity, basicity and pore sizes, recycling nature with same impact on
product distribution, easy separation, etc.
Consequently, this challenging task on achieving a selective allylation by the use of
simple and affordable method led us to explore this study by the use of a MMZCu(I)Y
catalyst and interesting results are discussed here.
Results and discussion
The optimization study of screening of catalysts and solvents is performed in which
phenol and allylbromide are used as model substrates and results are summarized in
Tables 1 and 2.
Either the presence of catalyst or base alone has not produced any significant result.
Similarly, there is no reaction with Na-exchanged zeolite (entry 1). However, KY has
produced considerable amount of allylated product but with no selectivity (entry 2).
Both O- and C-allylation occurred in other cases also like with LiY and CsY (entries 4
and 5). To check the influence of Bronsted acidity, we employed HY zeolite (entry 3),
but the yield is poor when compared with other cations. It is due to the acidic sites pre-
sent in HY prevents the formation of phenolate ion to attack by the allylating agent.
However, transition metals enhance the product yield with good selectivity towards
O-allylation by the expense of C-allylated product. Our recent research on the explor-
ation of multi-size porous material MMZ with various cations for fine selectivity
prompted us to employ them in the present study also. MMZNiY and MMZCu(II)Y have
produced 91% and 80% of allylation (entries 6 and 7), however, with considerable
amount of C-allylation also. Surprisingly, the Cu(I)Y zeolite has produced an excellent
amount of O-allylation selectively with a trace amount of C-allylation (entry 8). In fact,
this interesting result further incited us to employ MMZCu(I)Y and which produced only
O-allylation (entry 9) with almost same amount of yield. We have also examined the