Process for the preparation of tadalafil

1. A process for the preparation of tadalafil of Formula I

wherein the process comprises:

a) reacting a D-tryptophan compound of Formula III or a pharmaceutically acceptable salt thereof

 with a compound of Formula IV

 in the presence of sulfolane to obtain a cis-intermediate compound of Formula II;

b) optionally isolating the cis-intermediate compound of Formula II;

c) reacting the cis-intermediate compound of Formula II with a compound of Formula V

 in the presence of a base to obtain a compound of Formula VI;

d) reacting the compound of Formula VI with a compound of Formula VII; and

H 3 C—NH 2   Formula VII

e) isolating tadalafil of Formula I.

2. The process according to claim 1 , wherein step a) is carried out at a temperature of 50° C. to 100° C.