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A new transition state force field has been developed for the AD reaction, purely from quantum mechanical reference data. A new methodology was used for converting quantum mechanical normal modes into a form suitable for parametrization. The force field has been thoroughly validated by comparison to structural and energetic data, and by prediction of experimental enantioselectivities. Excellent agreement was observed, frequently within a few percent of the experimental enantioselectivity. The interactions responsible for enantioselectivity have been identified and compared to the Sharpless and Corey models.

Density functional calculations (Becke3LYP/6-31G(d)) on the (3 + 2) transition structures of osmium tetroxide mediated dihydroxylations of chiral allylic ethers show that the stereoselectivity is controlled by the “inside alkoxy effect” (Stork/Houk-Jäger model). In the special case of Z-disubstituted alkenes, 1,3-allylic strain (Kishi model) controls the stereoselectivity.

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The (2+2) cycloadditions of SO3 to ethene, propene, and 2-methylpropene were investigated with Hartree−Fock, MP2, QCISD(T), and hybrid Hartree−Fock/density functional theory (HF-DFT) methods. Experimental data support a (2+2) mechanism for these reactions. The thermally allowed (3+2) cycloadditions of SO3 to ethene and propene were also examined. With the exception of MP2 calculations, all levels of theory predict that SO3 reacts by a concerted (2+2) pathway. The transition structure has considerable zwitterionic character, and there is a strong preference for Markovnikov addition. The rearrangements of sulfites to sultones are disfavored. The origin of the large preference for the normally forbidden (2+2) process is attributed to frontier orbital interactions, and is contrasted to the (3+2) cycloaddition mechanism favored by OsO4.

Hexachlorocyclopentadiene undergoes Diels−Alder reactions with dienophiles possessing allylic chiral centers with moderate to excellent anti selectivity. Ab initio calculations on model systems elucidate the origin of this stereoselectivity which follow the “inside-alkoxy” model.

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