Synthesis of (−)-Morphine

The preparation of the diastereomerically pure β-tetralone ketal 4 is reported. Intramolecular alkylidene C−H insertion followed by hydrolysis of 4 proceeded to give the enantiomerically pure cyclopentene 15. The key step in this synthesis was the bis-intramolecular cyclization of keto aldehyde 2 to give the tetracyclic intermediate 20. Enone 20 was converted over several steps to (−)-morphine 1.