[reaction: see text] An efficient new method for constructing the 4a-methyltetrahydrofluorene skeleton was achieved via Friedel-Crafts intramolecular cyclization of 1,3-bis-exocyclic dienes. This strategy offers a simple and promising method for accessing complex structures.

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Bicyclic lactams derived from pyroglutamic acid provide a useful scaffold for synthesis of conformationally restricted analogues of lysine, ornithine and glutamine, as well as an Ala-Ala dipeptide analogue. Amino alcohol and carboxylic acid derivatives are accessible from a common intermediate. In this strategy, the bicyclic lactam system not only controls, but also facilitates the determination of the stereochemistry of the synthetic intermediates.