A novel and scalable synthesis of 5-fluoro-3-phenyl-2-[(1S)-1-(9H-purin-6-ylamino)propyl]-4(3H)-quinazolinone, idelalisib 1, has been developed.

Diethylene glycol dimethyl ether, diglyme, and 1,2-bis­(2-methoxyethoxy)­ethane, triglyme, are found to be suitable and safe alternate solvents to DMSO for the reduction of methanesulfonate in sodium borohydride. Addition of anhydrous lithium chloride led to the complete reduction of methanesulfonate esters to the corresponding alkanes in the presence of sodium borohydride in these solvents (diglyme and triglyme). This protocol is useful in the preparation of 1,2,3-triacetyl-5-deoxy-d-ribofuranoside, 7, a key intermediate of Capecitabine, 1, on the commercial scale.