Traceless Solid-Phase Synthesis of [6,7,8 + 5,6,7]-Fused Molecular Frameworks

B(C6F5)3/Chiral Phosphoric Acid Catalyzed Asymmetric Aza-Diels-Alder Reaction of Imines and Unactivated Dienes

Herein, we report an asymmetric aza-Diels-Alder reaction of quinoxalinones or benzoxazinones with unactivated dienes by utilizing a B(C6F5)3/chiral phosphoric acid catalyst to construct chiral six-membered N-heterocycles. Various quinoxalinones or benzoxazinones with electron-withdrawing and electron-donating groups and unactivated dienes were tolerated (up to 99% yield and 99% ee) in the methodology with only 2 mol % catalyst loading. Moreover, the luminescence mechanism and photophysical properties of the product were tested and used for anticounterfeiting of QR codes.

Synthesis of Hydroxylated Polycyclic Pyrrolo/Indolo[1,2-a]quinoxaline-Fused Lactam Derivatives via PhI(OAc)2-Promoted 1,2-Bond Migration and Solvent Insertion

PhI(OAc)₂-mediated ring expansion via 1,2-bond migration and concurrent solvent insertion generate hydroxylated polycyclic pyrrolo/indolo[1,2-a]quinoxaline-fused lactam derivatives in a highly diastereoselective fashion from spiro-fused quinoxalines in good-to-excellent yield. X-ray crystal structure analysis reveals that the polycyclic lactams are nonplanar molecules devoid of any symmetry as they possess one or two axially chiral biaryl or N-arylindolyl bridges along with one chiral center at the bridgehead carbon.

Traceless Solid-Phase Organic Synthesis

Traceless solid-phase synthesis represents an ultimate sophisticated synthetic strategy on insoluble supports. Compounds synthesized on solid supports can be released without a trace of the linker that was used to tether the intermediates during the synthesis. Thus, the target products are composed only of the components (atoms, functional groups) inherent to the target core structure. A wide variety of synthetic strategies have been developed to prepare products in a traceless manner, and this review is dedicated to all aspects of traceless solid-phase organic synthesis. Importantly, the synthesis does not need to be carried out on a linker designed for traceless synthesis; most of the synthetic approaches described herein were developed using standard, commercially available linkers (originally devised for solid-phase peptide synthesis). The type of structure prepared in a traceless fashion is not restricted. The individual synthetic approaches are divided into eight sections, each devoted to a different methodology for traceless synthesis. Each section consists of a brief outline of the synthetic strategy followed by a description of individual reported syntheses.