Process for preparing a phosphoramidite and further reaction thereof to the monophosphite

A process of preparing a compound of Formula (III) comprising the steps of:

• a) initially charging a compound of the formula (I):
• wherein R1, R2, R3 are selected from:
• —H, —(C1-C12)-alkyl, —O—(C1-C12)-alkyl, —(C6-C10)-aryl, —CN, NO2;
• b) adding P(NX2)3, where X is —(C1-C6)-alkyl;
• c) reacting the compound from a) and b) to give a compound of the formula (II):
• d) adding the compound of the formula (I):
• e) adding a compound Y, wherein Y is a five-membered ring in which at least one carbon atom has been replaced by a nitrogen atom;
• f) reacting the compounds from c) to e) to give a compound of the formula (III):