Exploiting the Ring Strain in Bicyclo[2.2.1]heptane Systems for the Stereoselective Preparation of Highly Functionalized Cyclopentene, Dihydrofuran, Pyrroline, and Pyrrolidine Scaffolds

The high strain of bicyclic systems drives retro-condensation reactions on bridgehead substituted bicyclo[2.2.1]hept-2-enes giving rise to orthogonally functionalized cyclopentene, 2,5-dihydrofuran, and 3-pyrroline scaffolds. Retro-Dieckman reactions were easily carried out on 3-tosyl-(7-carba/7-oxa/7-aza)bicyclo[2.2.1]hept-5-en-2-ones. Retro-aldol reactions of N-Boc-3-tosyl-7-azabicyclo[2.2.1]hept-5-en-2-ol and functionalized N-Boc-3-tosyl-7-azabicyclo[2.2.1]heptan-2-ols yield functionalized pyrrolidine scaffolds stereoselectively. The same reaction does not work with corresponding norbornene and 7-oxanorbornene derivatives.