Is phenyl a good migrating group in the rearrangement of organoborates generated from sulfur ylides?

Calculations show that the unexpected low phenyl migratory aptitude observed in reactions of mixed alkyl-aryl boranes with benzylic sulfur ylides can be attributed to (1) a conformational issue, (2) the reduction of the usual neighbouring effect of the phenyl in the transition state by the benzylic nature of the migrating terminus, (3) steric hindrance suffered by the larger phenyl group migrating to the hindered migrating terminus and this despite (4) the increase in the barrier to alkyl migration by the presence of a 'non-migrating' phenyl on the boron atom.

Highly regioselective and diastereoselective epoxidation of allylic amines with Oxone.

Allylic amines (as their protonated ammonium salts) can be epoxidised with high syn diastereoselectivity and regioselectivity at the proximal alkene in substrates with several double bonds using Oxone. The protonated ammonium cation activates the Oxone by hydrogen bonding, thus promoting the oxidation of groups within the vicinity of the complex.

Synthesis and applications of chiral organoboranes generated from sulfonium ylides.

The reactions of aryl-stabilized sulfonium ylides with trialkyl/triarylboranes have been investigated. Clean monohomologation of the boranes with only a small amount of the higher homologation products (<10%) was observed. The homologation products were isolated as the alcohols (treatment with H2O2/NaOH) and amines (treatment with NH2OSO3H).

Highly diastereoselective Simmons-Smith cyclopropanation of allylic amines.

[reaction: see text] Cyclopropanation of allylic tertiary amines using the Simmons-Smith reagent has been achieved by employing chelating groups in close proximity to the amine. The chelating groups promote cyclopropanation at the expense of N-ylide formation. Using pseudoephedrine as the chelating group, high diastereoselectivity is observed.

Tandem formation and [2,3] rearrangement of methylene ammonium ylides derived from amines and the Simmons-Smith reagent.

[reaction: see text] Zinc-complexed methylene ammonium ylides are formed from tertiary amines and the Simmons-Smith reagent. These stable entities can be activated with n-BuLi to allow reactions typical of ammonium ylides such as [2,3] rearrangements. In the case of oxazolidine 12, ylide formation, activation, and subsequent [2,3] rearrangement was highly efficient and occurred with very high diastereoselectivity.