The present invention provides a compound of formula (I), wherein n is 0, 1 or 2; R.sup.1 represents halo, a C.sub.1-4alkyl group which is optionally substituted by one or more fluoro, a C.sub.1-4alkoxy group which is optionally substituted by one or more fluoro and wherein when n is 2 the substituents R.sup.1 may be the same or different; R.sup.2 represents an unbranched C.sub.2-7alkyl group; R.sup.3 represents H or OCH.sub.3; and W represents O or S and pharmaceutically acceptable salts and prodrugs thereof, to processes for preparing such compounds, to their utility in treating clinical conditions associated with insulin resistance, to methods for their therapeutic use and to pharmaceutical compositions containing them.