C‑8-Selective Allylation of Quinoline: A Case Study of β‑Hydride vs β‑Hydroxy Elimination Deepti Kalsi, † Roshayed A. Laskar, † Nagaraju Barsu, † J. Richard Premkumar, ‡ and Basker Sundararaju* ,† † Fine Chemical Laboratory, Department of Chemistry, Indian Institute of Technology Kanpur, Kanpur, Uttar Pradesh 208016, India ‡ Center for Molecular Modelling, Indian Institute of Chemical Technology, Hyderabad 500007, India * S Supporting Information ABSTRACT: An unprecedented C(8)-H bond allylation of quinoline with allyl carbonate and allyl alcohol catalyzed by Cp*Co(III) using a traceless directing group via β-oxygen and β-hydroxy elimination is described. This site-selective allylation reaction proceeds smoothly with various functional group tolerance including quinoxaline and phenanthridine. Under the nonoxidative reaction conditions, the difference in selectivity between Rh(III) and Co(III), which proceeds through β-hydride and β-hydroxy elimination using allyl alcohol, is shown for the first time. O ver the past decade, activation of C-H bonds emerged as an important tool for atom- and step-economic syn- thesis. 1 In particular, Cp*Rh(III) has attained its pinnacle over the past few years for a vast number of synthetic trans- formations through C-H bond functionalization. 2,3 Due to its meager resources and its extortionate prices, however, we need an alternative for bringing our research to a more pragmatic or industrial level. In 2013, Kanai and Matsunaga showed Cp*Co(III), which is not only an alternate catalyst for its noble counterpart [Rh(III)] but also unique in its reactivity and selectivity. 4 However, often the requirement of strong chelating groups such as pyridine and its analogues disfavors its expediency in practical applications. 5 Glorius, 6 Chang, 7 Matsunaga, 8 Ackermann, 9 Sundararaju, 10 and others 11 circum- vented this problem recently in a few cases, but the potential for exploiting the unique reactivity of Cp*Co(III) is still great when weakly chelating/traceless directing groups are used. At the outset of our continuous efforts to examine new reactivity of Cp*Co(III) which includes oxidant-free annula- tion, 10d sequential C-H activation/oxygen atom transfer, 10b C(sp 3 )-H bond alkenation, 10a and C-H bond allylation using allylic substrate including allyl alcohol are reported in this study. Direct allylation of arenes and heteroarenes are of significant value due to its efficacious modification of olefins upon allylation. Though Cp*Co(III)-catalyzed allylation of C- H bonds was demonstrated by Glorius under mild conditions, this required a strong chelating group such as pyridine or its analogues and activated allylic substrate such as carbonate or acetate. 12 Later, Kanai/Matsunaga and Glorius showed that activation of allyl alcohol with other directing groups including amide proceeds via a β-hydroxy elimination pathway using Co(III) as a catalyst. 13 It was in contrast with allylation shown by Glorius and others with Rh(III) and Ru(II) under oxidative conditions, which proceeds via β-hydride elimination path- way. 14 This distinctive behavior of Co(III) and Rh(III) raised our curiosity to explore further reactions which can answer a few more queries. (1) Is β-hydroxy elimination substrate dependent or catalyst dependent? (2) If it is catalyst (metal) dependent, why did Rh(III) gave poor yield compared to Co(III) (for example, see ref 13c)? (3) Do properties of group 9 elements (Co, Rh, Ir) such as atom size, electronic configuration, nucleophilicity, and oxophilicity have any effect in elimination pathway? (4) Can we obtain β-hydroxy and β- hydride elimination products selectively with allyl alcohol using two different metals from group 9 under the same reaction conditions (preferably nonoxidative conditions)? To gain perspicuity and understanding to answer the above questions, we decided to scrutinize our results on allylation with simultaneous use of Co(III) and Rh(III) employing allyl alcohol as a coupling partner. Owing to the higher activity exhibited against hepatitis by 8-allylquinoline and its lack of presence in the literature for direct synthesis of this novel compound, 15a we studied the sequential allylation/alkene metathesis catalysis and selective linkage of functionalized alkenes for further applications. 15b These multifold advantages encouraged us to choose quinoline N-oxide as a traceless directing group for remote C-H bond allylation. In order to establish the reactivity of Cp*Co(III) for C-H bond allylation with quinoline N-oxide, we have chosen allyl carbonate as the coupling partner, Cp*Co(III) as a catalyst, and carboxylate as an additive in trifluoroethanol as solvent. To determine the best conditions for the reaction, various catalysts, additives, and temperatures were screened thoroughly, and the optimization Received: June 25, 2016 Letter pubs.acs.org/OrgLett © XXXX American Chemical Society A DOI: 10.1021/acs.orglett.6b01845 Org. Lett. XXXX, XXX, XXX-XXX