155 Bulgarian Chemical Communications, Volume 44, Number 2 (pp.155 – 158) 2012 A Novel Route for the Synthesis of Six- and Seven- Membered 6-Trimethylsilylspiro[4,n]alk-6-enes M. A. Venkatesha, S. HariPrasad* Department of Post Graduate Studies in Chemistry, Central College Campus, Dr. B. R. Ambedkar Veedhi, Bangalore University, Bangalore – 560001, India Received: June 14, 2011; accepted: July 18, 2011 A novel route for the synthesis of 6-trimethylsilylspiro[4,5]dec-6-ene and 6-trimethylsilylspiro[4,6]undec-6-ene by the Wurtz-Fittig type coupling reaction of 6-iodospiro[4,5]dec-6-ene and 6-iodospiro[4,6]undec-6-ene with alkali metals and chlorotrimethylsilane in good yields is reported. The compounds serve as a new class of spiranyl cyclic vinylanionic synthons. Key words: spiranes, cyclic vinylsilanes, anionic synthons, Wurtz-Fittig reaction. 1. INTRODUCTION Cyclic vinylsilanes are an important class of compounds in organic synthesis [1]. The compounds serve as masked vinylanionic synthons [2]. Spirocyclics on the other hand, are important compounds with diverse properties, which are found to occur as subunits in many natural products [3]. To our knowledge, there is only one report on the preparation of spiranyl cyclic vinylsilanes in the literature by Paquette [4]. Substitution of the trimethylsilyl group in simple spirocyclic compounds alters the electronic properties of the molecules, thereby providing a route for easy functionalization with diverse functional groups [5]. We had earlier prepared a wide variety of simple and substituted cyclic vinylsilanes by the Wurtz- Fittig coupling reaction of the corresponding cyclic vinyl bromides/chlorides with sodium and chlorotrimethylsilane in different anhydrous solvents [6]. The most recent of the substituted cyclic vinylsilanes synthesized by us are the 2- trimethylsilylcycloalkenones [7]. The compounds are α-acylvinyl anionic synthons [8]. During our study on the synthesis of the 2- trimethylsilylcycloalkenones, we found 6- trimethylsilyl-7-methyl-1,4-dioxaspiro[4,5]dec-6- ene to be highly unstable even in the mildest acidic medium [9]. The 6-trimethylsilyl-7-methyl-1,4- dioxaspiro[4,5]dec-6-ene could not be isolated under the conditions of our work, even though the compound has been isolated by Yus [10]. Therefore, we chose to prepare the corresponding carbon equivalents, which are the spiranyl- compounds. These novel spiranyl cyclic vinyl silanes are expected to be very stable. 2. EXPERIMENTAL IR spectra were recorded on a Shimadzu FT-IR 8400S spectrometer. NMR spectra were recorded on a Bruker AMX 400 MHz spectrometer. GC was run on a Shimadzu 14-B/Mayura 9800 Gas Chromatograph using a SE-30 SS 2m × 1/8” column. Yields refer to the isolated yields of the products. GC-MS spectra were obtained using a Shimadzu GC-MS QP 5050A. General procedure for the preparation of spiro[4, n]alkanones Spiro[4,n]alkanones (3 and 4): To a magnetically stirred suspension of potassium tert- butoxide (2.2 mol equivalents) in 100 mL refluxing anhydrous benzene was added a mixture of cycloalkanone (10 g) and 1,4- dibromobutane (1.2 mol equivalents) over a period of 40 min. After completion of the addition, the mixture was further refluxed for 10 hrs. The reaction mixture was cooled, diluted with 50 mL ether and added to 100 mL of ice cold water. The organic layer was separated, and the aqueous layer was extracted with ether (3×50 mL). The combined organic extracts were washed with water (2×50 mL), brine (2×30 mL) and dried over anhydrous potassium carbonate. The solvent was removed on a rotary evaporator and distilled in vacuo to isolate spirocyclic ketones 3 and 4 in yields as reported in the literature. * To whom all correspondence should be sent: e-mail: hariprasad@bub.ernet.in © 2012 Bulgarian Academy of Sciences, Union of Chemists in Bulgaria