Iterative protecting group-free cross-coupling leading to chiral multiply arylated structures.

The Suzuki-Miyaura cross-coupling is one of the most often utilized reactions in the synthesis of pharmaceutical compounds and conjugated materials. In its most common form, the reaction joins two sp(2)-functionalized carbon atoms to make a biaryl or diene/polyene unit. These substructures are widely found in natural products and small molecules and thus the Suzuki-Miyaura cross-coupling has been proposed as the key reaction for the automated assembly of such molecules, using protecting group chemistry to affect iterative coupling.

Borohydrides from organic hydrides: reactions of Hantzsch's esters with B(C(6)F(5))(3).

We report herein that the reaction between a series of Hantzsch's ester analogues 1 a-d with the Lewis acidic species B(C(6)F(5))(3) results in facile transfer of hydride to boron. The main products of this reaction are pyridinium borohydride salts 2 a-d, which are obtained in high to moderate yields. The N-substituted substrates (N-Me, N-Ph) reacted in high yield 90-98 % and the connectivity of the products were confirmed by an X-ray crystallographic analysis of the N-Me borohydride salt 2 a.

Cross coupling reactions of chiral secondary organoboronic esters with retention of configuration.

We report the first example of a coupling reaction of chiral secondary boronic esters generated by the hydroboration of vinyl arenes. In order for the reaction to take place in high yields, the use of silver oxide as a base and the presence of at least 8 equiv of triphenyl phosphine per Pd are required. The reaction proceeds with >90% retention of configuration in all cases except one.