From conventional to greener catalytic approaches for carbohydrates etherification
The synthesis of ethers derived carbohydrates/polyols used as intermediates in multistep synthesis or large scale commodity products such as detergents is since a long time an issue of concern for organic chemists. The conventional Williamson reaction is the most used synthetic method to build an ether function from a free hydroxyl group. Very selective transformations that use this procedure have been achieved and progresses based on this reaction are always of actuality. Alternatively to the Williamson reaction, catalytic approaches aiming at opening salt free accesses to ethers have more recently emerged. This evolution is pushed by the growing interest dedicated to greener synthetic approaches that find a particular echo in the field of carbohydrates chemistry. This chapter sets up a panorama of the methods used to access ethers derived from the free hydroxyl groups of carbohydrates/polyols. This overview of course includes the stoichiometric Williamson reaction, largely and even, in some cases, routinely employed at the laboratory and industrial scales. A particular attention is given to the recent developments in protecting groups for multistep synthesis and the large scale production of alkylcelluloses. New approaches based on the use of homogeneous or heterogeneous catalysis have more recently emerged and now offer a new panel of reactions to build ether functions. Several examples of salt free acid or metal catalyzed reactions transformations are depicted, thus showing progresses that have been and remain to be done in this field.