An efficient gold(III)-catalyzed general method for the diastereoselective allylation of six-membered cyclic hemiacetals at room temperature is developed. The present protocol is operationally simple with good functional group tolerance, thus providing easy access to various multifunctionalized 2,6-trans-disubstituted tetrahydropyrans. Since an allyl moiety is readily introduced, the developed strategy is highly versatile and has great potential for further functional group manipulation. Furthermore, a diastereoselective synthesis of the C1–C13 fragment of bistramide A and B has been described highlighting this methodology.