Method for producing 6-alkoxy-(6H)-dibenz [c,e] [1,2]-oxaphosphorines

A process for preparing 6-alkoxy-(6H)-dibenzo [c,e][1,2] oxaphosphorins, wherein 6H-dibenzo [c,e][1,2]oxaphosphorin 6-oxides of the formula I

• where R3, R4=alkyl, alkoxy, alkylthio, alkenyl, alkynyl, aryl, heteroaryl, cycloalkyl groups are used as the reactant, further comprising, carrying out the following steps:
• 1) providing at least one solvent,
• 2) adding the reactant
• 3) adding an ortho ester and
• 4) adding alcohol if it has not already been used under step 1).