T. Bandiera

Selectivity in cycloadditions—XI: Cycloadditions of nitrile oxides to methyl styryl sulfides, sulfoxides and sulfones. regiochemistry

Abstract E and Z methyl styryl sulfides undergo highly regioselective cycloadditions with benzo and mesitonitrile oxide. The regioselectivity is lower with sulfoxides and is reversed in the case of sulfones. The directing effect of the thio moieties has been clarified in the framework of the frontier model of cycloaddition reactions. The lower effect of the thio substituents in the cycloadditions of cyclic dipolarophiles depends upon the nodal properties of their FOs.

Selectivity in cycloadditions XII: the directive effect of enol ethers and thioenol ethers in cycloadditions of nitrile oxides

Abstract Cycloadditions of nitrile oxides to 2,3-dihydrofuran are highly regioselective whereas the regioselectivity of the cycloadditions to 2,3-dihydrothiophen is only moderate. The directing effect of oxygen and sulfur in these cycloadditions could be evaluated at 2.8 and 1.1 Kcal mol -1 respectively. The related acyclic sulfur dipolarophiles, ( E )-propenyl methyl and phenyl sulfides, similarly undergo cycloadditions with moderate regiochemistry. The different regioselectivities and reactivities of the dipolarophiles can be related to differences in energies and shapes of their highest occupied orbitals, which are also responsible for the diverging behaviour observed in the electrophilic reactions and 2 + 2 cycloadditions of enol and thioenol ethers.

Cycloadducts of benzonitrile oxide to pyridine. A case of a two-step cycloaddition

Abstract Pyridine adds benzonitrile oxide in apolar solvents, affording fair yields of bisadducts III and IV. Quinoline and isoguinoline afford isolable monocycloadducts VIII and IX.

Addition of pyridine and isoquinoline to benzoylcarbonitrile oxide

Abstract Addition of pyridine to benzoylcarbonitrile oxide affords a fragile zwitterionic adduct, which slowly reverts to the addends, leading ultimately to benzoyl isocyanate and products deriving from it. A moderately stable cycloadduct is obtained in the reaction with isoquinoline.

A Convenient Procedure for the Synthesis of Ursodeoxycholic Acid Sulfated Derivatives

Abstract The mono- and bis(sulfooxy) derivatives of ursodeoxy-cholic acid are, contrary to a previous report, easily prepared by a very simple direct sulfation procedure.