1,3-dioxanomorphides and 1,3-dioxanocodides

A compound of Formula I:

• or a pharmaceutically acceptable salt thereof, wherein:
• G is R1 or a hydroxyl protecting group PG;
• R1 is hydrogen, C1-6 alkyl, C2-4 alkenyl, C2-4 alkynyl, C3-6 cycloalkyl(C1-4)alkyl, or C6-10 aryl (C1-4)alkyl, wherein the C3-6 cycloalkyl, and C6-10 aryl, portions thereof are optionally substituted with 1, 2, or 3 substituents, each independently selected from the group consisting of hydroxy, halo, halo(C1-4)alkyl, amino, C1-4 alkylamino, di(C1-4)alkylamino, carboxy, and C1-4 alkoxycarbonyl;
• PG is selected from the group consisting of methyl, tert-butyl, benzyl, benzovl, acetyl, trimethyl silyl, tert-butyldimethyl silyl, tert-butyldiphenyl silyl, and tri-isopropyl silyl;
• R2 is
• (a) hydrogen;
• or
• (b) C1-6 alkyl, C2-6 alkenyl, C2-6 alkynyl, C3-7 cycloalkyl(C1-4)alkyl, C3-7 cycloalkenyl(C1-4)alkyl, or C6-10 aryl(C1-4)alkyl, any of which is optionally substituted with 1, 2, or 3 substituents, each independently selected from the group consisting of hydroxy, halo, halo(C1-4)alkyl, amino, C1-4 alkylamino, di(C1-4)alkylamino, carboxy, and C1-4 alkoxycarbonyl;
• R3 and R4 are each independently selected from the group consisting of hydrogen, C1-6 alkyl, C2-6 alkenyl, and C2-6 alkynyl, wherein any of which, when other than hydrogen, is optionally substituted with 1, 2, or 3 substituents, each independently selected from the group consisting of hydroxy, halo, halo(C1-4)alkyl, amino, C1-4 alkylamino, di(C1-4)alkylamino, carboxy, and C1-4 alkoxycarbonyl;
• R5 is selected from the group consisting of hydrogen, C1-6 alkyl, C2-6 alkenyl, C2-6 alkynyl, C3-7 cycloalkyl, C3-7 cycloalkenyl, phenyl, and naphthyl wherein any of which, when other than hydrogen, is optionally substituted with 1, 2, or 3 substituents, each independently selected from the group consisting of hydroxy, halo, halo(C1-4)alkyl, amino, C1-4 alkylamino, di(C1-4)alkylamino, carboxy, and C1-4alkoxycarbonyl;
• and
• is a single bond or a double bond.