Synthesis of stemofurans C, L and T using organomanganese arene chemistry; Revised structure for stemofuran L William H. Miles a, * , Cassidy M. Madison a , Christopher Y. Kim a , Daniel J. Sweitzer a , Shelby D. Valent a , Dasan M. Thamattoor b a Department of Chemistry, Lafayette College, Easton, PA 18042, USA b Department of Chemistry, Colby College, Waterville, ME 04901, USA article info Article history: Received 28 June 2017 Received in revised form 19 September 2017 Accepted 21 September 2017 Available online 23 September 2017 Keywords: Organomanganese arene Stemofuran Benzofuran Nucleophile abstract The synthesis of stemofurans C, L and T was achieved using organomanganese arene complexes. The critical carbon-carbon bond between the C-2 position of benzofuran and the arene was established in a regioselective manner directed by the cationic manganese tricarbonyl moiety. Oxidation of the resulting dienyl complexes and cleavage of the methyl ethers gave the desired stemofuran products. The spec- troscopic data for the originally proposed structure for stemofuran L did not match the synthesized material, which prompted the synthesis of an isomer that did match the spectroscopic data. This revised structure has been proposed as the correct structure for stemofuran L. © 2017 Elsevier B.V. All rights reserved. 1. Introduction Nucleophilic attack on arenes coordinated to transition metals is one of the most important modes of reactivity in organometallic chemistry [1]. Organomanganese arene complexes, which have been exploited in many studies [1b,2-7], are notable for their greater reactivity compared to the more extensively studied orga- nochromium arene complexes [1a,1c]. The reactivity of nucleo- philes with h 6 -arene complexes, in which electron-donating groups such as alkoxy and amino groups direct the nucleophile to the meta-position, complements the standard electrophilic aro- matic addition reactions to arenes [1e 7]. The addition of carbon nucleophiles to organomanganese arene complexes possessing electron-donating substituents typically follows this pattern, but there are a couple of noteworthy exceptions [3b,6]. Steric repulsion inherent in more highly substituted arenes complexes (such as the (3-methoxyestrone)Mn(CO) 3 þ ) [3b] and/or the nature of the car- bon nucleophile [6] leads to diminished selectivity. Even with these potential complications, the general selectivity of these reactions for nucleophilic attack at the meta-position to alkoxy groups sug- gested a straightforward method for the synthesis of some 2- arylbenzofurans, compounds that have become increasingly important [8e10]. Benzofurans represent a broad class of biologically important compounds [8]. 2-Arylbenzofurans, an important subset of ben- zofurans, have been isolated from various plants, and possess bio- logical activity including antifungal, antibacterial, and anticancer properties [9,10]. The Stemona genus is a particularly rich source of 2-arylbenzofurans named stemofurans. The stemofurans are char- acterized by C-3 0 and C-5 0 oxygenation on the arene ring, and methylation on the arene and/or benzofuran rings, with additional oxygenation frequently occurring on the benzofuran moiety [9]. Some representative examples include stemofurans C (1a), T (1b), and L (1c; originally proposed structure). In the course of our synthetic studies, we suspected that 1c, the originally proposed structure for stemofuran L, was incorrect based on the comparison between the literature values of the NMR peaks and compound 1c that we synthesized, and that isomeric 1d was the correct structure (Fig. 1). There have been many synthetic strategies employed for the synthesis of 2-arylbenzofurans, in particular the SuzukieMiyaura coupling of 2-(boronic acid)benzofurans with the appropriate aryl bromide [11,12]. This method depends on ready access to the necessary aryl bromide, which sometimes poses synthetic chal- lenges with standard electrophilic aromatic substitution chemistry. We recognized that a subset of stemofurans and related 2- * Corresponding author. E-mail address: milesw@lafayette.edu (W.H. Miles). Contents lists available at ScienceDirect Journal of Organometallic Chemistry journal homepage: www.elsevier.com/locate/jorganchem https://doi.org/10.1016/j.jorganchem.2017.09.034 0022-328X/© 2017 Elsevier B.V. All rights reserved. Journal of Organometallic Chemistry 851 (2017) 218e224