Pnictogen‐Bonding Catalysis: An Interactive Tool to Uncover Unorthodox Mechanisms in Polyether Cascade Cyclizations

Abstract

Pnictogen‐bonding catalysis and supramolecular σ‐hole catalysis in general is currently being introduced as the non‐covalent counterpart of covalent Lewis acid catalysis. With access to anti‐Baldwin cyclizations identified as unique characteristic, pnictogen‐bonding catalysis appeared promising to elucidate one of the hidden enigmas of brevetoxin‐type epoxide opening polyether cascade cyclizations, that is the cyclization of certain trans epoxides into cis‐fused rings. In principle, a shift from SN2‐ to SN1‐type mechanisms could suffice to rationalize this inversion of configuration. However, the same inversion could be explained by a completely different mechanism: Ring opening with C−C bond cleavage into a branched hydroxy‐5‐enal and the corresponding cyclic hemiacetal, followed by cascade cyclization under conformational control, including stereoselective C−C bond formation. In this report, a pnictogen‐bonding supramolecular SbV catalyst is used to demonstrate that this unorthodox polyether cascade cyclization mechanism occurs.

Halogen Bonding of N‐Halosuccinimides with Amines and Effects of Brønsted Acids in Quinuclidine‐Catalyzed Halocyclizations

“…We believe the systematic evidence and specific findings described herein not only provides new mechanistic guidance in understanding haloaddition and halocyclization reactions of alkenes and alkynes, especially those catalyzed by quinuclidine‐bearing cinchona alkaloids as illustrated by the groups of Yeung , Tang , Henneke , Denmark , Ishihara , Yamamoto and others, [33–42,61–78] but also provides fundamental knowledge in expanding halogen bond‐based reactions in synthesis, particularly concerning iodine‐based reagents and amine catalysis. Wider implications of the current work to chalcogen‐ and pnictogen‐based Lewis acids, which similarly feature sigma‐hole acceptor capabilities, is an intriguing proposition and represents a growing field of applications in catalysis, anion‐transport and may even be considered a less ‘unorthodox’ approach to the design of new reactions and methods in the future [79–84] …”

On the Importance of Pnictogen and Chalcogen Bonding Interactions in Supramolecular Catalysis

“…In the field of organocatalysis, the number of studies devoted to the development of new functional PnB-based catalysts has rapidly increased during recent years [93][94][95][96][97][98][99][100][101][102]. In this section, several selected examples involving PnB-based catalysts are discussed.…”

“…In this case, both TS3 and 4 are also stabilized by Sb•••Cl PnBs, which is similar to the Reissert-type substitution of isoquinolines, resulting in the corresponding ester. Additionally, Matile's group has carried out several studies on ether cyclization reactions [94][95][96]98]. In their study [96], Hao and collaborators carried out a comparative ) of compound 1 (B3LYP/def2-TZVP level of theory) [93].…”

“…In this case, both TS3 and 4 are also stabilized by Sb•••Cl PnBs, which is similar to the Reissert-type substitution of isoquinolines, resulting in the corresponding ester. Additionally, Matile's group has carried out several studies on ether cyclization reactions [94][95][96]98]. In their study [96], Hao and collaborators carried out a comparative The authors also achieved success in catalyzing the more challenging transformation of 1-chloroisochromane to an ester, a reaction that proceeds through chloride abstraction in TS3 and successive attack of a silyl enol ether (see Figure 4b).…”

The Phosphorus Bond, or the Phosphorus-Centered Pnictogen Bond: The Covalently Bound Phosphorus Atom in Molecular Entities and Crystals as a Pnictogen Bond Donor

“…The variety of these interactions is a consequence of the variability of the nature of the electron density donor and acceptor participating in the molecular assembly and therefore depends on factors such as the local geometry (bond distance and intermolecular approach angle) and the electron density profile of the interacting atomic basins. Since acid–base interactions are central to chemical reactions [ 6 ], recognition processes [ 7 , 8 ], bond functionalization [ 9 ], catalysis [ 10 , 11 , 12 ], and self-assembly [ 13 , 14 , 15 ], a fundamental understanding and exploration of these interactions has been one of the key issues in the rapid development of research areas such as computational chemistry [ 16 , 17 , 18 , 19 ], crystallography [ 5 , 20 ], and crystal engineering [ 21 , 22 ].…”