Synthesis and characterization of N-phenyl pyrrole anchored to Fischer carbene complex through ring closing metathesis oxidative aromatization and various aryl substituted Fischer carbene complexes R. Ganesamoorthi, Arunabha Thakur, D. Sharmila, V. Ramkumar, Sundargopal Ghosh * Department of Chemistry, Indian Institute of Technology Madras, Chennai 600 036, India article info Article history: Received 4 October 2012 Received in revised form 11 December 2012 Accepted 12 December 2012 Keywords: Fischer carbene complex Ring closing metathesis Oxidative aromatization N-heterocycle Group 6 transition metal abstract Ring closing metathesis of pentacarbonyl[(ethoxy)(N,N-diallyl anilyl)carbene]tungsten(0) complex, [(CO) 5 W]C(OCH 2 CH 3 )C 6 H 4 N(CH 2 CH]CH 2 ) 2 ], 1 leads to the formation of pentacarbonyl[(ethoxy)(N- phenyl 2,5-dihydro pyrrolyl)carbene]tungsten(0) complex, [(CO) 5 W]C(OCH 2 CH 3 )C 6 H 4 N (CH 2 CH] CH 2 ) 2 ], 2 in good yield. Further, complex 2 undergoes oxidative aromatization to afford N-phenyl pyrrole anchored to alkoxy carbene, 3. In addition, a number of aryl substituted carbene complexes [(CO) 5 W] C(OCH 2 CH 3 )C 6 H 4 R], 4e7 (4:R ¼ OCH 2 CH 3 ; 5:R ¼ OCH 2 CH]CH 2 ; 6:R ¼ OCH]CHCH 2 CH 2 CH 2 CH 2 CH 3 ; 7: OC 6 H 5 Br) have been synthesized from the reaction of 1-(allyloxy)-4-bromobenzene with W(CO) 6 in presence of various concentration of n-BuLi and Meerwein’s salt. All the complexes have been isolated in moderate to good yields and have been characterized by 1 H NMR, 13 C NMR, IR, UVevis spectroscopic techniques and the solid state structures of 1 , 2 and 4 have been unequivocally established by X-ray diffraction analysis. Ó 2012 Elsevier B.V. All rights reserved. 1. Introduction Since after the discovery of Fischer carbene complex in 1964 [1], it has been extensively used during past few decades and it is one of the most versatile organometallic reagents for organic synthesis. The number and utility of different types of reactions of these complexes that have been reported [2e4], are far too numerous to list. It has been widely reported that variations in the substituents of the carbene-unit often lead to novel and unprecedented reac- tivity trends. Reports focused on the utility of these organometallic reagents in the synthesis of heterocyclic compounds have not been much explored [5]. Therefore, it is desirable to draw the attention of people involved in organic synthesis mediated or catalyzed by organometallic reagents to the potential of Fischer-type carbene complexes for accessing different types of heterocycles. In recent years, the metathesis reaction has become one of the most important CeC bond forming processes and has been utilized extensively in total synthesis [6e10]. The advent of well defined catalyst systems, combined with excellent activity and broad functional group compatibility, has been the major factor for popularizing the metathesis reaction [11e 13]. One of the most commanding strategies for the synthesis of carbocyclic and heterocyclic frameworks is ring closing metathesis (RCM) [14,15]. However, in the context of aromatic and heteroaromatic ring formation, rationally designed RCM strategies have only recently been highlighted in the literature [16]. Indeed, many early exam- ples of the synthesis of aromatic compounds by RCM were viewed as unwanted degradation reactions [17]. A compound containing heteroaromatic moiety attached with alkoxy Fischer carbene complex was found to be highly demandable in the field of chemistry and biology. In the course of our ongoing investigations on the reactivity of Fischer carbene complexes, we have observed the formation of several unusual products and subsequent reaction of one of the products with Grubb’s catalyst produces a N-hetero- cycle bearing Fischer carbene complex. We report herein the synthesis and characterization of pentacarbonyl[(ethoxy)(N-phenyl pyrrolyl)carbene]tungsten(0) complex via a RCM-oxidative aromatization and several aryl substituted Fischer carbene complexes. 2. Results and discussion 2.1. Synthesis and characterization of compounds 1e3 There are several reports available in the literature that depict the oxidative aromatization of N-aryl dihydropyrroles upon * Corresponding author. Tel.: þ91 44 2257 4230; fax: þ91 44 2257 4202. E-mail address: sghosh@iitm.ac.in (S. Ghosh). Contents lists available at SciVerse ScienceDirect Journal of Organometallic Chemistry journal homepage: www.elsevier.com/locate/jorganchem 0022-328X/$ e see front matter Ó 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.jorganchem.2012.12.014 Journal of Organometallic Chemistry 726 (2013) 56e61