Synthesis of phosphitylated compounds using a quaternary heterocyclic activator

A method for preparing a phosphoramidite comprising the step of reacting a hydroxyl containing compound with a phosphitylating agent in the presence of an activator having the formula I

• wherein
• R is alkyl, cycloalkyl, aryl, aralkyl, heteroalkyl, or heteroaryl;
• R1 and R2
• are H or define a 5- or 6-membered ring;
• X1 and X2
• are independently N or CH;
• Y is H or Si(R4)3, wherein R4 is alkyl, cycloalkyl, aryl, aralkyl, heteroalkyl, or heteroaryl;
• and
• B− is a deprotonated acid.

A mixture of an activator having the formula I

• wherein
• R is alkyl, cycloalkyl, aryl, aralkyl, heteroalkyl, or heteroaryl;
• R1 and R2
• are H or define a 5- or 6-membered ring;
• X1 and X2
• are independently N or CH;
• Y is H or Si(R4)3, wherein R4 is alkyl, cycloalkyl, aryl, aralkyl, heteroalkyl, or heteroaryl;
• and
• B− is a deprotonated acid;
• and
• an additive;
• wherein said additive is a compound having the formula VIII
• wherein
• R is alkyl, cycloalkyl, aryl, aralkyl, heteroalkyl, or heteroaryl;
• R1 and R2
• are H or define a 5- or 6-membered ring;
• and
• X1 and X2
• are independently N or CH;
• or
• pyridine;
• and wherein the molar ratio of activator to additive is in the range of from 1:1 to 1:10.