Exploring the unique reactivities of heterobicyclic tetrazoles—access to functionally diverse and versatile heterocyclic scaffolds

The benzylic hydrogen atom in oxabicyclic tetrazoles such as (6R,8R)-(8-phenyl-5,6-dihydro-8H-tetrazolo[5,1-c][1,4]oxazin-6-yl)-alkanols (A, X=CH2OH) is highly acidic, being alkylated in preference to a hydroxymethyl group with NaH and active alkyl halides. The enantioenriched products B now contain a phenyl and alkyl group on a stereogenic benzylic carbon atom. The products are subject to β-elimination to give 1-{1-[3-propenyl]-1H-tetrazol-5-yl}-1-phenyl-alkanols. Cleavage of the propenyl chain leads to chiral non-racemic 1-phenyl-1-(1H-tetrazol-5-yl)-alkanols C. Free-radical ‘anomeric’ azidation of the oxabicyclic tetrazoles followed by reduction and ring closure with inversion of configuration produces azabicyclic tetrazoles D as constrained functionalized piperazines.