Visible Light Mediated Sulfenylation-Annulation Cascade of Alkyne Tethered Cyclohexadienones Akshay M. Nair, a Shreemoyee Kumar, a and Chandra M. R. Volla a, * a Department of Chemistry, Indian Institute of Technology Bombay, Powai, Mumbai-400076, India E-mail: chandra.volla@chem.iitb.ac.in Manuscript received: July 15, 2019; Revised manuscript received: August 28, 2019; Versionofrecordonline: ■■■,■■■■ Supporting information for this article is available on the WWW under https://doi.org/10.1002/adsc.201900874 Abstract: A mild and facile method to access sulfenylated dihydrochromenones via a visible light mediated thiol-yne/conjugate addition cascade of alkyne-tethered cyclohexadienones, using cheap and readily available organic photoredox catalyst (Eosin Y) is demonstrated. The utility and sustainability of the protocol were further justified by the high yields, excellent diastereoselectivities, broad substrate scope, gram scale synthesis, green chemistry metrics (atom economy and efficiency) and further synthetic transformations of the products. Keywords: Cyclohexadienone; Thiol; visible-light; hetero annulation; Eosin Y Introduction The quest for energy efficient and sustainable synthesis has seen the emergence of visible light photocatalysis as an important tool for promoting a wide range of synthetic transformations for the formation of C À C and C À X bonds. [1] Photocatalysis has proven to be one of the most sustainable tools for the generation of radical ion intermediates under mild conditions. On the other hand, cascade cyclizations belong to a powerful class of transformations for the construction of carbocyclic and heterocyclic skeletons from relatively simple acyclic motifs. [2] Along these lines, alkyne-tethered cyclohexadienones have been extensively studied for the formation of fused carbocycles. [3–7] The formation of 5,6-fused carbocycles (cis-hydrobenzofuranones) has been well explored using metal catalysts like Rh, [3] Pd, [4] Cu, [5] and Ni. [6] In contrast, the formation of 6,6- fused carbocycles remains relatively unexplored. In a pioneering report, Lam and co-workers demonstrated an arylative cyclization of cyclohexadienones for the formation of cis-dihydrochromenones under Ni- catalysis. [7a] Later, they also developed an efficient Ir- catalyzed visible light mediated sulfonylative cycliza- tions using sulfonylazides (Scheme 1a). [7b] Very re- cently, Ackermann and Li reported a low valent cobalt catalyzed difluoroalkylative cascade cyclization of alkyne tethered cyclohexadienones using stoichiomet- ric amounts of metallic zinc as reducing agent. [8] Despite these elegant studies, the use of rare, expensive and toxic metal catalysts in these protocols, adds to environmental concerns and potentially limits their large scale utility. So the development of a metal-free, organocatalytic cascade annulation of alkynylcyclohex- adienones is highly desired, yet remains elusive. During the preparation of this manuscript, Xu and co- workers reported a metal free cascade annulation of alkyne-tethered cyclohexadienones with diselenides using stoichiometric amounts of base under visible light irradiation (Scheme 1b). [9] Organosulfur compounds are extremely important entities due to their extensive applications in various Scheme 1. Overview of the work. FULL PAPER DOI: 10.1002/adsc.201900874 Adv. Synth. Catal. 2019, 361,1–7 © 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim 1 These are not the final page numbers! ��