Stereospecific ring expansion from orthocyclophanes with central chirality to metacyclophanes with planar chirality

Abstract

Carbon-carbon bonds constitute the major framework of organic molecules and carbonhydrogen bonds are abundant in their peripheries. Such nonpolar s-bonds are thermodynamically stable and kinetically inert in general. Nonetheless, selective activation of those ubiquitous bonds may offer a straightforward method to construct and/or functionalize organic skeletons. Herein we describe ring expansion from orthocyclophanes to metacyclophanes occurring upon sequential action of light and a metal catalyst. Formally, specific non-strained carbon-hydrogen and carbon-carbon bonds are cleaved and exchanged without elimination of any leaving groups. Notably, the product is energetically uphill from the starting material, but the endergonic photocyclization step makes it possible to drive the transformation forward. The ring expansion is extended to the stereospecific synthesis of metacyclophanes possessing planar chirality, during which central chirality on a tertiary carbon is transferred to planar chirality.

Chiral exploration of 6,12‐diphenyldibenzo[b,f][1,5]diazocine with stable conformation

“…Recently, the concept of conformational chirality based on axial and planar chiral molecules has become a topic of intense interest. [7][8][9][10][11][12][13][14][15] Different kinds of structures with the restricted rotation of σ-bonds such as biaryls, cyclophanes, and strained cyclic alkenes have been developed for asymmetric catalysis, functional materials, supramolecular chemistry, targets of total synthesis, and so on. [16][17][18][19][20] Increasing the conformational stability gives higher chances for optical resolution of conformationally chiral molecules.…”

“…Classic chirality based on sp hybridized stereogenic centers has been well investigated, while less emphasis has been devoted to inherent chirality induced only by special molecular conformation. Recently, the concept of conformational chirality based on axial and planar chiral molecules has become a topic of intense interest . Different kinds of structures with the restricted rotation of σ‐bonds such as biaryls, cyclophanes, and strained cyclic alkenes have been developed for asymmetric catalysis, functional materials, supramolecular chemistry, targets of total synthesis, and so on …”

Chemoselective Nitrosylation of Anilines and Alkynes via Fragmentary or Complete NO Incorporation

“…[7][8][9][10][11] Although various methodologies involving enamine and imine intermediates have been developed in organic synthesis, [12][13][14][15][16][17][18] single-electron oxidation of electron-rich enamine intermediates to trigger radical reactions is still rare despite the high activity of the in-situ-generated radical intermediates. [19][20][21][22] Recently, reactions through C-H [23][24][25][26][27] and C-C [28][29][30][31][32][33][34] cleavage have been powerful strategies for direct transformation of simple substrates. Thus, the combination of a single-electron transfer (SET) process with the generation of very active radical intermediates and C-H/C-C functionalization would potentially open the door to a new field of reaction discovery.…”

Strain Release Chemistry of Photogenerated Small‐Ring Intermediates

“…The rhodium‐mediated ring‐opening was assumed to occur under central‐to‐planar chirality transfer as the coordinating benzene facilitates a site‐selective migration of the ipso ‐sp 2 ‐carbon onto the rhodium center. The bulky COD‐ligand was assumed to prohibit the ring flipping across the newly expanded ansa‐chain afterwards [70] …”