Synthesis of Efavirenz by an innovative cost effective cyclisation process

The present invention relates to a novel process fo r the preparation of (4S)-6-chloro-4-(cyclopropylet hynyl)-1, 4- dihydro-4-(trifluoromethyl)-2H-3, 1-benzoxazin-2-on e (Efavirenz) of Formula I with simple and commerci ally available urea.