Tandem [4+2]/[3+2] Cycloadditions of 1,3,4-Oxadiazoles with Alkenes

A review on the tandem [4+2]/[3+2] cycloaddition reactions of 1,3,4-oxadiazoles with alkenes is presented. This reaction presents a powerful synthetic tool in the construction of complex polycyclic molecules in a one-pot reaction. Special attention is paid to synthesis of [n]polynorbornane and oxanorbornyl systems. In continuation, a review on the 1,3,4-oxadiazole reactions used in stereoselective total synthesis of alkaloids is given. Both intermolecular and intramolecular tandem [4+2]/[3+2] reactions are discussed. Stereospecificities and mechanistic rationale of various reactions are supported by quantum-chemical calculations (RHF/6-31G*).