4-[bis(dimethylamino)phosphoryloxy]-2-(1-hydroxy-2-trityloxyethyl)-3-phenylmethoxy-2H-furan-5-one;[1-[4-[bis(dimethylamino)phosphoryloxy]-5-oxo-3-phenylmethoxy-2H-furan-2-yl]-2-hydroxyethyl] propanoate;4-[2-[4-[bis(dimethylamino)phosphoryloxy]-5-oxo-3-phenylmethoxy-2H-furan-2-yl]-2-propanoyloxyethoxy]-4-oxobutanoic acid;[2-[4-[bis(dimethylamino)phosphoryloxy]-5-oxo-3-phenylmethoxy-2H-furan-2-yl]-2-propanoyloxyethyl] 4-oxopentanoate;[1-[4-[bis(dimethylamino)phosphoryloxy]-5-oxo-3-phenylmethoxy-2H-furan-2-yl]-2-trityloxyethyl] propanoate