Catalytic Functionalisation of sp3 Bonds

Reported herein is an investigation into palladium-catalysed -allylation employing sulfonamide nucleophiles. Anions of benzylsulfonamides have been shown to react with a series of allyl acetates in the presence of Pd0 catalysts, phosphine ligands and base at room temperature, enabling the synthesis of sp3-functionalised sulfonamides. The developed methodology has allowed access to a library of novel allylated sulfonamides, varying both amine substituent and allylic functionality. In addition, we have applied our methodology to a series of known sulfonamide drug targets, to demonstrate our reaction as a useful late-stage functionalisation tool, whilst populating chemical space.

The performed mechanistic study using a stereospecific electrophile confirms benzylsulfonamides behave as soft carbon nucleophiles in the Tsuji-Trost reaction, as a ‘net retention’ of stereochemistry is observed (confirmed by X-ray crystallography).

Moreover, the asymmetric synthesis of allylated sulfonamides is probed, although obtaining enantioselectivity a- to SO bonds is naturally difficult, due to the conformational preferences of sulfonamide carbanions.

Traditional methods for direct -alkylation of sulfonamides require strong bases, reactive electrophiles, low temperatures and use of stoichiometric amounts of additives. Therefore, in addition to a catalytic method, we report an alternative method reacting benzylsulfonamides with allyl bromide electrophiles via a nucleophilic substitution reaction, using mild conditions (LDA, THF at –20 °C).