Compound of Formula IIc (Formula IIa where R15, R16 and R17 are H, R41 is P, R43 is M1R58, where M1 is O or NR57 and R58 is optionally substituted aryl or optionally substituted heteroaryl) is prepared by reacting compound of Formula IId (Formula IIa where R15, R16 and R17 are H, R41 is P, and R43 is a halogen, R59, e.g. chloro) with a compound of Formula R58???OH or of Formula R58???NR57 in the p