Stereoretentive Regio- and Enantioselective Allylation of Isoxazolinones by a Planar Chiral Palladacycle Catalyst

The catalytic allylic substitution is one of the most important tools in asymmetric synthesis to form C-C bonds in an enantioselective way. While high efficiency was previously accomplished in terms of enantio- and regiocontrol using different catalyst types, a strong general limitation is a very pronounced preference for the formation of allylic substitution products with (E)-configured C=C double bonds. Herein, we report that with a planar chiral palladacycle catalyst a diastereospecific reaction outcome is achieved using isoxazolinones and allylic imidates as substrates, thus maintaining the C=C double bond geometry of the allylic substrates in the highly enantioenriched products. DFT calculations show that the reactions proceed via an SN 2 mechanism and not via π-allyl Pd complexes. Crucial for the high control is the stabilization of the allylic fragment in the SN 2 transition state by π-interactions with the phenyl substituents of the pentaphenylferrocenyl catalyst core.

An efficient synthesis of benzothiazole using tetrabromomethane as a halogen bond donor catalyst

A CBr₄ catalyzed simple, mild, and efficient protocol has been developed for the synthesis of 2-substituted benzothiazole from 2-aminothiophenols and N-methylthioamides under solvent free conditions.

Sulfinyl-Mediated Stereoselective Overman Rearrangements and Diels-Alder Cycloadditions

Sulfinyl trichloroacetamides are readily obtained in excellent yields through a highly stereoselective Overman rearrangement. Related bis-allylic substrates lead to amido 2-sulfinyl butadiene derivatives in excellent yields, with total chemo- and diastereoselectivity. These amido dienyl sulfoxides undergo highly selective Diels-Alder cycloadditions with N-phenylmaleimide with remarkable stereocontrol by the sulfoxide moiety.

Asymmetric synthesis of allylic amines via hydroamination of allenes with benzophenone imine

Rhodium-catalyzed highly regio- and enantioselective hydroamination of allenes is reported. Exclusive branched selectivities and excellent enantioselectivities were achieved applying a rhodium(i)/Josiphos catalyst. This method permits the practical synthesis of valuable α-chiral allylic amines using benzophenone imine as ammonia carrier.

Dual Palladium(II)/Tertiary Amine Catalysis for Asymmetric Regioselective Rearrangements of Allylic Carbamates

The streamlined catalytic access to enantiopure allylic amines as valuable precursors towards chiral β- and γ-aminoalcohols as well as α- and β-aminoacids is desirable for industrial purposes. In this article an enantioselective method is described that transforms achiral allylic alcohols and N-tosylisocyanate in a single step into highly enantioenriched N-tosyl protected allylic amines via an allylic carbamate intermediate. The latter is likely to undergo a cyclisation-induced [3,3]-rearrangement catalysed by a planar chiral pentaphenylferrocene palladacycle in cooperation with a tertiary amine base. The otherwise often indispensable activation of palladacycle catalysts by a silver salt is not required in the present case and there is also no need for an inert gas atmosphere. To further improve the synthetic value, the rearrangement was used to form dimethylaminosulfonyl-protected allylic amines, which can be deprotected under non-reductive conditions.