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O-Allylation of phenols with allylic acetates in aqueous media using a magnetically separable catalytic system
Citation:
Saha, A., J. LEAZER, AND R. S. VARMA. O-Allylation of phenols with allylic acetates in aqueous media using a magnetically separable catalytic system. GREEN CHEMISTRY. RSC Publishing, Cambridge, Uk, 14(1): 67-71, (2012).
Impact/Purpose:
To inform the public.
Description:
Allylic ethers were synthesized in water using magnetically recoverable heterogeneous Pd catalyst via O-allylation of phenols with allylic acetates under ambient conditions. Aqueous reaction medium, easy recovery of the catalyst using an external magnet, efficient recycling, and the high stability of the catalyst renders the protocol economic and sustainable. Allyl ethers are important starting materials for a wide range of organic reactions, including the hydrogen shift, sigmatropic rearrangement, and polymerization reactions in addition to being a popular protecting groups for alcohols. The traditional method for the synthesis of allyl ethers is the Williamson-type ether synthesis which involves the use of strongly basic metal alkoxide anion and highly active allyl halides or their equivalents. Comparatively the addition of oxygen nucleophiles to h3- allylmetal complex of various transition metals (Pd,4 Ru,5 Ir,6 Ni7) provides an attractive mild alternative approach for their synthesis using much less reactive allyl alcohols, allyl esters or allyl carbonates. However, most of the existing methods for transition metal catalyzed O-allylation via h3-allylmetal intermediate are accomplished using non-recyclable homogeneous catalyst in various toxic organic solvents such as THF, DMF, benzene, toluene, DCM under inert atmosphere. The use of heterogeneous catalysts in organic transformations has become an interesting area of research in the field of green chemistry facilitating catalyst recyclability as exemplified in a recent report by Kobayashi et. al. wherein a heterogeneous polymer incarcerated Pd catalyst is used for O-allylation of phenols in THF medium. Magnetic nano-ferrite [Fe3O4] has been widely used by our group and others as the solid support for various catalysts because of their easy recovery using an external magnet. In continuation of the work with magnetically separable nano ferrite [Fe3O4] as heterogeneous catalyst support, has been immobilized on the surface of dopamine-functionalized nanoparticles (Fig. 1), ([Fe3O4-Dopamine-Pd]); their use as an easily recyclable catalyst to develop an economic and eco-friendly green synthesis of allyl ethers by O-allylation of phenols with allylic acetates in water under open aerial atmosphere has been explored.
