Calcium-catalysed synthesis of amines through imine hydrosilylation: an experimental and theoretical study

A method to reduce aldimines through hydrosilylation is reported. The catalytic system involves calcium triflimide (Ca(NTf₂)₂) and potassium hexafluorophosphate (KPF₆) which have been shown to act in a synergistic manner. The expected amines are obtained in fair to very high yields (40-99%) under mild conditions (room temperature in most cases). To illustrate the potential of this method, a bioactive molecule with antifungal properties was prepared on the gram scale and in high yield in environmentally friendly 2-methyltetrahydrofuran. Moreover, it is shown in this example that the imine can be prepared in situ from the aldehyde and the amine without isolating the imine. The mechanism involved has been explored experimentally and through DFT calculations, and the results are in accordance with an electrophilic activation of the silane by the calcium catalyst.

A Ba/Pd Catalytic System Enables Dehydrative Cross-Coupling and Excellent E-Selective Wittig Reactions

A Ba/Pd cooperative catalysis system was developed to enable the dehydrative cross-coupling of allylic alcohols with P-ylides to occur directly and promote a subsequent Wittig reaction in one pot. A variety of multisubstituted 1,4-dienes were isolated in good to excellent yields with broad P-ylides (stabilized by both ester and ketone carbonyl groups) and aldehyde (aliphatic and aromatic) substrates with excellent E selectivity.

Regiospecific formal [3 + 2] annulation of tert-propargyl alcohols with acyclic 1,3-diketones via the cycloisomerization of homoallenyl ketones

A one-pot, regiospecific synthesis of dihydrofurans bearing a quaternary centre is developed from the formal [3 + 2] annulation of tert-propargyl alcohols and 1,3-diketones through the S_N2^I mechanism to form homoallenyl ketone and a subsequent cycloisomerization reaction.

Highly Regioselective Synthesis of Oxindolyl-Pyrroles and Quinolines via a One-Pot, Sequential Meyer-Schuster Rearrangement, Anti-Michael Addition/C(sp3)-H Functionalization, and Azacyclization

A one-pot, sequential Meyer-Schuster (MS) rearrangement of oxindole-derived propargyl alcohols to the corresponding α,β-unsaturated enones and their anti-Michael addition, followed by intramolecular azacyclization is described in a highly regioselective manner using Ca(OTf)₂ as the promoter. Further, we described the one-pot MS rearrangement, followed by C_(sp³)-H functionalization of 2-methyl azaarenes at α-carbon of these doubly activated alkenes. Control experiments and computational calculations were performed to propose the reaction mechanism.

A diversity-oriented synthesis of cyclopenta[b]pyrroles and related compounds through a calcium(ii)/copper(ii) catalytic sequence

A sequential bicatalytic route relying on calcium(ii) and copper(ii) salts is described to provide access to original nitrogen-containing heterocycles.

Mild, calcium catalysed Beckmann rearrangements

A mild calcium catalysed Beckmann rearrangement has been realised, which forgoes the more traditional harsh reactions conditions associated with the transformation.

Acid-catalysed intramolecular addition of β-ketoesters to 1,3-dienes

1,3-Dienyl β-keto esters are cyclised into bicyclolactones using the Bi(OTf)₃/TfOH catalytic system. This reaction represents a rare case of simultaneous C-C and C-O bond formation at positions 1 and 3 of a 1,3-diene. Application to the synthesis of ramulosin is presented.