DOI:10.1002/adsc.200505211 Thiophenol-Mediated 1,5-Hydrogen Atom Abstraction: Easy Access to Mono- and Bicyclic Compounds Florent Beaufils, a Fabrice De ´ne `s, a Barbara Becattini, a Philippe Renaud, a, * Kurt Schenk b a Universität Bern, Departement für Chemie und Biochemie, Freiestrasse 3, CH-3000 Bern 9, Switzerland Fax: ( þ 41)-31-631-3426, e-mail: philippe.renaud@ioc.unibe.ch b Laboratoire de Cristallographie 1, EPFL SB IPMC LCR1, BSP 521, CH-1015 Lausanne, Switzerland Received: May 22, 2005; Accepted: August 1, 2005-09-01 Supporting Information for this article is available on the WWW under http://asc.wiley-vch.de/home/. Abstract: A thiophenol-mediated method for cycliza- tion of alkynes is described. The reaction cascade in- volves the intermolecular addition of a phenylthiyl radicaltoaterminaltriplebondgeneratinganalkenyl radical,followedbya1,5-hydrogenatomtransferand a5-exo-trigradicalcyclization.Thisveryefficienttin- freeprocedureallowsonetopreparehighlyfunction- alized cyclopentane derivatives as well as fused bicy- clic and spirocyclic compounds from easily available precursors. During this cyclization process, a phenyl- thio moiety is incorporated into the final cyclized products. This functionalization is particularly attrac- tive for further transformation of the products. Keywords: alkynes; cyclization; hydrogen transfer; radicals; spiro compounds; sulfur Introduction Radicalreactionsrepresentavaluabletoolfororganic synthesis. [1] For instance, carbon-carbon bonds can be formedundermildconditionswithauniquefunctional group tolerance. Moreover, radical reactions can be highlyregio-andstereoselectiveandtheirabilitytobe involved in cascade reactions makes them particularly attractive. The use of hydrogen atom abstraction is of particularinterestsinceitallowsfunctionalizationofre- mote unreactive positions without using of transition metal catalysts. [2] The highly reactive alkenyl radicals aresuitableprecursorsforefficientintramolecular1,5- hydrogen abstraction at C  H bonds. After transloca- tion,thenewradicalspeciescancyclizetogiveacyclo- pentanederivative(Scheme1). [3–5] Thealkenylradicalsareusuallypreparedbyreaction of the corresponding vinyl halide with a stannyl radi- cal. [3–5] The pioneering work of Curran demonstrated the potential of this reaction [see Scheme1, Eq.(1)] and following this work many applications have been developed. [2,6] However,thepracticabilityofthisproc- essishamperedbytheuseoftinderivativesandbythe formationofuncyclizedproduct via directreductionof theintermediatealkenylradical.Radicaladditiontoter- minalordisubstitutedalkynesoffersanattractivealter- nativeforthegenerationofalkenylradicalsthatunder- go1,5-translocationtoalkylradicalsand5-exo-trigcy- clization (related reactions involving the formation of heterocycles via transientsilyl, [7,8] alkoxyl [9,10] andimid- yl [11] radicalsarealsoreported).Inter-andintramolecu- laradditionsofcarbon-centeredradicalsareutilizedto initiate such cascade processes. [4,12–14] Bachi and later Alcaide employed the intermolecular radical addition oftinhydride [15,16] andmorerecently,inparalleltothe presentwork,wedevelopedadialkylphosphite-mediat- edreaction. [17] Thiylradicalsareeasilygeneratedfromthiolsanddi- sulfidesandaddefficientlyinareversiblemannertocar- bon-carbonmultiplebondsleadingtocarbon-centered radicals. [18,19] Theresultingradicalshavebeenextensive- Scheme1. 1,5-Hydrogen transfer-cyclizationprocess. FULL PAPERS Adv. Synth. Catal. 2005, 347,1587–1594 # 2005 Wiley-VCH Verlag GmbH&Co. KGaA, Weinheim 1587