A General Method for Making Bicyclic Compounds with Nitrogen at a Bridgehead—Application to the Halichlorine Spiro Subunit.

N-Protected β-amino aldehydes having the nitrogen in a ring are easily converted into Morita–Baylis–Hillman adducts; O-acetylation and N-deprotection result in spontaneous cyclization to bicyclic structures having nitrogen at a bridgehead.