Conformational analysis of highly hindered thiophosphoramidates

The conformational analyses in solution and in solid state of the highly crowded mobile systems, 2-dicyclohexylamino-2-thio-1,3,2λ5-dioxaphosphinane (1), 2-dicyclohexylamino-2-thio-trans-4,6-dimethyl-1,3,2λ5-dioxaphosphinane (trans-2) and their anancomeric analogs, ax-2-dicyclohexylamino-2-thio-cis-4,6-dimethyl-1,3,2λ5-dioxaphosphinane (ax-cis-2) and eq-2-dicyclohexylamino-2-thio-cis-4,6-dimethyl-1,3,2λ5-dioxaphosphinane (eq-cis-2) are informed. In accordance with proton–proton and proton–phosphorus coupling constants, the dioxaphosphinane ring adopts a chair conformation in all compounds except in the case of trans-2, which was found in a twisted conformation. Solid state structural analyses suggest that only the synaxial Me/NR2 or Me/S interactions in trans-2, force the heterocycle ring to remain as a mixture of twisted boat and half-chair (chaise loungue) conformers.