Role of additives and solvents in the synthesis of chiral isoreticular MOF-74 topologies

Chiral induction is a simple and inexpensive approach to synthesise chiral metal–organic frameworks, even when using achiral building-blocks. The challenge lies in selecting the proper chiral inductor. This can only be achieved upon understanding the mechanism behind the chirality transfer from the chiral guest to the achiral MOF. In this work, the role of two types of chiral additives and different solvents was investigated in the crystallization of isoreticular MOF-74. We show that pyrrolidone-based solvents can interact with the framework walls and influence the thermal stability of the MOF. The role of the different chiral additives is related to the strength of their interaction with the MOF. Unlike cinchona alkaloids that have weak interactions with the framework, l- or d-trans-4-hydroxyproline (l- or d-Hyp) can strongly bind to the Zn²⁺ metal centres and cause the twisting of the organic linker. Moreover, l- and d-Hyp additives can affect the IRMOF-74 nucleation process depending on their concentration and handedness.

Strongly interacting chiral additives play a complex role during the crystallisation of chiral isoreticular MOF-74. They can coordinate to the open sites of the metal ions and induce strain on the framework, leading to a local twisting of the organic linker.

Syntheses of Highly Functionalized Spirocyclohexenes by Formal [4+2] Annulation of Arylidene Azlactones with Allenoates

A straightforward phosphine-catalyzed formal [4+2] annulation between α-branched allenoates and arylidene azlactones has been developed to access highly functionalized spirocyclohexenes. This cyclization favors the γ-addition of the phosphine-activated allenoates over a β'-addition pathway. Detailed computational studies support the proposed mechanism and provide a reasonable explanation for the observed regioselectivity and the noted effect of the catalyst.

Thio-Michael addition of α,β-unsaturated amides catalyzed by Nmm-based ionic liquids

Most substrates work well for this transformation in water, and the IL-catalyst is recyclable and applicable for gram-scale synthesis.

[Ce(l-Pro)2]2 (Oxa) as a heterogeneous recyclable catalyst: synthesis of pyrazoles under mild reaction conditions

A highly efficient method for the synthesis of pyrazoles mediated by [Ce(l-Pro)₂]₂ (Oxa) as a heterogeneous catalyst.