Phenanthroline Derivatives as Efficient Organic Photocatalysts for Visible-Light-Mediated PET-RAFT Polymerization

Phenanthroline is an excellent and stableπ-electron acceptor with a large conjugated chromophore.Phenanthroline derivatives are widely used in adsorption,photodegradation,solar cells,biology,and so on.At present,there are still limited organic molecules utilized to efficiently photocatalyze reversible-deactivation radical polymerization(RDRP).Therefore,the design of organic photocatalysts(OPCs)for RDRP remains a challenge.Herein,according to the strategy of combining the donor groups and weak acceptor groups,donor-acceptor(D-A)type OPCs based on phenanthroline were utilized for the first time in photoinduced electron transfer-reversible addition-fragmentation chain transfer(PET-RAFT)polymerization.1,10-Phenanthroline-5-amine(Aphen)with a donor group-amino was screened out for efficacious photo-controlled radical polymerization under blue light for various monomers with conjugated and unconjugated structures with high monomer conversion and well-defined narrow dispersity polymers(Đ<1.20).Controllable homo-polymers and block copolymers were successfully realized by chain extension reaction and block copolymerization of structurally diverse monomers.

Total Synthesis of Starfish Cyclic Steroid Glycosides.Part 1,Synthesis of the Aglycone and Attempts at Installation of the Sugar Units

Comprehensive Summary Sepositoside A(1)is the major and first cyclic steroid glycoside isolated from starfishes,which features a strained 16-membered ring formed by tethering C3 and C6 of the steroid aglycone with a linear trisaccharide.We conceived a convergent synthetic plan in which sepositoside A was disconnected into a disaccharide and a steroid-glucose hybrid ether.The desired 3β,6β-dihydroxy-Δ7,8-23-one aglcyone was readily prepared from dehydroepiandrosterone in 12 steps.The etherification of the 6β-hydroxy-Δ7,8-steroid with a variety of hexopyranoside-C6-electrophiles and CO_(2)-extrusion of a steroid-pyranose hybrid carbonate were extensively studied;however,formation of the desired steroid-pyranose etherate linkage has not been successful.Model studies on theβ-selective installation of the(1→2)-linked disaccharide onto the steroidal C3β-OH with the corresponding disaccharideα-imidates were also examined,however,formation of theα-glycosides prevailed.The present results force us to explore alternative approaches to construct the steroid-pyranose etherate linkage and stepwise assembly of the glycans en route to the starfish cyclic steroid glycosides,which will be presented in two articles that follow.