Thiophene bioisosteres of spirocyclic σ receptor ligands. 1. N-substituted spiro [piperidine-4, 4′-thieno [3, 2-c] pyrans]

~61%

~52%

~%

~69%

~93%

~%

~79%

~%

~64%

~46%

~76%

~%

~69%

~%

~97%