COMMUNICATIONS 362  WILEY-VCH Verlag GmbH, D-69451 Weinheim, 2000 0570-0833/00/3902-0362 $ 17.50+.50/0 Angew. Chem. Int. Ed. 2000, 39, No. 2 Carbocyclic Ring Closure of Unsaturated S-, Se-, and C-Aryl Glycosides Matthieu Sollogoub, Jean-Maurice Mallet, and Pierre Sinay È* The glycoside-to-carbocycle transformation [1] provides an attractive route for the synthesis of functionalized carbocycle derivatives from readily available sugar precursors. Usually these transformations rely on the cleavage of the glycosidic acetal functionality to liberate the reactive carbonyl group that undergoes carbocyclization. [1b] The disadvantage of these approaches is the loss of the aglycon. Furthermore it is impossible to apply this method to sugars bearing unusual aglycons, particularly C-glycosides, where no acetal function- ality is present. Herein, we report the first direct trans- formation of hex-5-eno S-, Se-, and C-glycosides into carbo- cycles with retention of the aglycon. We reported that hex-5-enopyranosides such as 1 undergo reductive rearrangement with triisobutylaluminum (TIBAL) to afford highly substituted cyclohexane derivatives such as 2, [2] where both the aglycon moiety and anomeric configu- ration are retained [3] (Scheme 1). The key step in this trans- formation is the endo cleavage of the glycosidic bond to give a stabilized carbocationic intermediate A, which then recyclizes and undergoes reduction to afford the observed major product 2. O OMe BnO OBn BnO O OMe BnO BnO BnO OMe BnO OBn BnO OH endo cleavage A reduction 1 2 (major product) cyclization Scheme 1. The key step of the TIBAL-promoted rearrangement: endo- glycosidic cleavage (the detailed mechanism of this process is not known). Bn  benzyl. We assumed that it should be possible to replace the methoxy group by other electron-donating groups that would stabilize the analogous carbocationic intermediate B and therefore promote endo cleavage (Scheme 2). However, when the known C-glucoside 3 [4] was treated with five equivalents of TIBAL at 50 8C, we failed to observe the desired carbocycle In conclusion, this method represents a novel, efficient and selective synthesis of (Z)-vinyl bromides through a simple addition. [12] The ability to obtain both trans- and cis-haloal- kylation of alkynes is synthetically useful as well as mecha- nistically intriguing. Current work is focused on further elucidation of the mechanism and expansion of the scope of the reaction. Received: July 2, 1999 [Z 13668] Revised: October 4, 1999 [1] [1] For examples see: Comprehensive Organometallic Chemistry II, Vol. 12 (Eds.: E. W. Abel, F. G. A. Stone, G. Wilkinson, L. S. Hegedus), Pergamon, Oxford, 1995 ; N. A. Saccomano in Compre- hensive Organic Synthesis, Vol. 1 (Eds.: B. M. Trost, I. Fleming, S. L. Schreiber), Pergamon, Oxford, 1991, pp. 193 ± 201. [2] Some examples: S. H. Pine, Org. React. 1994, 43, 1; D. A. Ager, Org. React. 1990, 38, 1; B. E. Maryanoff, A. B. Reitz, Chem. Rev. 1989, 89, 863. [3] D. S. Matteson, Tetrahedron 1989, 45, 1859. [4] E. Takada, S. Hara, A. Suzuki, Tetrahedron Lett. 1993, 34, 7067. [5] B. M. Trost, Angew. Chem. 1995, 107 , 285 ; Angew. Chem. Int. Ed. Engl. 1995, 34, 259. [6] B. M. Trost, A. B. Pinkerton, J. Am. Chem. Soc. 1999, 121, 1988. [7] For previous use of this catalyst in our group see: B. M. Trost, A. Indolese, T. J. J. Müller, B. Treptow, J. Am. Chem. Soc. 1995, 117 , 615; B. M. Trost, T. J.J. Müller, J. Martinez, J. Am. Chem. Soc. 1995, 117 , 1888; B.M. Trost, M. Portnoy, H. Kurihara, J. Am. Chem. Soc. 1997 , 119, 836. [8] T. P. Gill, K. R. Mann, Organometallics 1982, 1, 485. [9] All new compounds have been characterized spectroscopically, and elemental composition has been established by combustion analysis or high resolution mass spectrometry; see Supporting Information. [10] For several examples of cis-halometalations see: H. Dietl, H. Reinheimer, J. Moffatt, P.M. Maitlis, J. Am. Chem. Soc. 1970, 92, 2276; K. Kaneda, T. Uchiyama, Y. Fujiwara, T. Imanaka, S. Teranishi, J. Org. Chem. 1979, 44, 55; R. Hua, S. Shimada, M. Tanaka, J. Am. Chem. Soc. 1998, 120, 12 365. [11] For a trans-chloroalkylation see: Z. Wang, X. Lu, Chem. Commun. 1996, 535. For a stoichiometric cis-chlororuthenation of acetylenedi- carboxylates see: P. R. Holland, B. Howard, R. J. Mawby, J. Chem. Soc. Dalton Trans. 1983, 231. [12] M. Hulce, M. J. Chapdelaine in Comprehensive Organic Synthesis, Vol. 4 (Eds.: B. M. Trost, I. Fleming, M. F. Semmelhack), Pergamon, Oxford, 1991, pp. 279 ± 287. [*] Prof. P. Sinay È, Dr. M. Sollogoub, Dr. J.-M. Mallet De  partement de Chimie Associe  au CNRS, Ecole Normale Supe  rieure 24 rue Lhomond, 75231 Paris cedex 05 (France) Fax: ( 33) 1-44-32-33-97 E-mail: pierre.sinay@ens.fr Supporting information for this article is available on the WWW under http://www.wiley-vch.de/home/angewandte/ or from the author.