J. zyxwvutsr Org. Chem. zyxwvu 1995,60, zyxwvu 8351-8359 8361 Reductive Oxa Ring Opening of 7-Oxabicyclo[2.2.1] heptan-2-ones. Synthesis of C-a-Galactosides of Carbapentopyranoses Janine Cossy,*~~ Jean-Luc Ranaivosata,+ Vbronique Bellosta,+Jacek Ancerewicz,* Rafael Ferritto,* and Pierre Vogel*,* zyxwv Laboratoire de chimie organique associt? au CNRS, ESPCI, 10, rue Vauquelin, F-75281 Paris Cedex, France, and Section de Chimie de l‘Universit6, BCH, 1015 Lausanne-Dorigny, Switzerland Received June 19, 1995@ Photoinduced electron transfer from Et3N to zyxwvu 7-oxabicyclo[2.2.llheptan-2-ones can generate the corresponding 3-hydroxycyclohexanonederivatives. The method has been applied to the synthesis of C-a-D-galactopyranosides of carbapentopyranoses. Radical a-D-galactosidation of zyx (*)- ~1RS,4RS,5RS,6RS)-6-endo-methoxy-3-methylidene-5-exo-~phenylseleno)-7-oxabicyclo[2.2. llhept- 2-one ((33-61) followed by seleno-Pummererrearrangement and reduction with Bu3SnH gave (+)- (1R,2S,3S,4R,6R)- ((+)-68) and (+)-(1S,2R,3R,4S,6S)-3-endo-methoxy-5-oxo-6-endo-[(2’,3’,~,~-~tra- O-acetyl-a-~-galactopyranosyl~methyll-7-oxabicyclo~2.2.llhept-2-endo-yl acetate ((+)-69), which were separated by column chromatography. Irradiation (254 nm) in the presence of Et3N gave (+I- (lS,2&3R,6R)- ((+)-60) and (+)-(1R,2S,3S,6S)-2-hydroxy-6-methoxy-4-0~0-3-[(2’,3’,~,6’-tetra-O- acetyl-a-D-galactopyranosyl)methyllcyclohexyl acetate (+)-61, respectively. NaBH4 reduction and acetylation provided (+)-(lS,2S,3R,4R,5R)- ((+)-62) and (+)-(1R,2R,3S,4S,5S)-5-methoxy-2-[(2’,3’,4’,6’- tetra-O-acetyl-a-~-galactopyanosyl)methyllcyclohexa-1,3,4-triyl triacetate ((+)-a). Introduction Optically pure 7-oxabicyclo[2.2. llheptd-en-2-yl deriva- tives (+)-l, (-)-2, (+)-3, and (-1-3 (“naked sugars” of the first generationll and (+)-4, zyxwvuts (-)-6, (+)-6, and (-)-6 (“naked sugars” of the second generationI2have become useful chirons in the preparation of natural products and analogues3 and of compounds of biological i n t e r e ~ t . ~ Introduction of substituents at their (331, C(5), and C(6) centers can be carried out with high stereo~ontrol.~ Except for 7-oxabicyclo[2.2.1lheptane derivatives bearing an electron-releasing substituent at C(1),6 the opening of the oxa bridge requires relatively drastic conditions, which in some cases might lead to water e1imination.I Derivatives having one carbanion-stabilizing substituent + Ecole Superieure de Physique et de Chimie Industrielles (ESPCI). @ Abstract published in Advance ACS Abstracts, November 15,1995. (1) (a) Vieira, E.; Vogel, P. Helv. Chim. Acta 1983, 66, 1865. Reymond, J.-L.; Vogel, P. Tetrahedron: Asymmetry 1990, I, 729. (b) Saf, R.; Faber, K.; Penn, G.; Grjengl, H. Tetrahedron 1988, 44, 389. (c) Ronan, B.; Kagan, H. B. Tetrahedron: Asymmetry 1991,2, 75. (d) Corey, E. J.; Loh, T.-P. Tetrahedron Lett. 1993,34, 3979. (2) Vogel, P.; Auberson, Y.; Bimwala, M.; de Guchteneere, E.; Vieira, E.; Wagner, J. In Trends in Synthetic Carbohydrate Chemistry; Horton, D., Hawkins, L. D., McGarvey, G. J., Eds.; ACS Symposium Series 386: American Chemical Societv: Washineton. D.C.. 1989: D 197.Voeel. Universite de Lausanne. P.; Fattori, D.; Gasparini, F.; Le Drian, C’: Syhlett 1990,1?3. VogecP: Bull. SOC. Chim. Belg. 1990, 99, 295. (3) (a) Kernen, P.; Vogel, P. Tetrahedron Lett. 1993, 34, 2473. (b) Sevin, A.-F.; Vogel, P. J. Org. Chem. 1994, 59, 5920. (c) Kernen, P.; Vogel, P. Helv. Chim. Acta 1995, 78, 301. Bialeki, M.; Vogel, P. Ibid. 1995, 78, 325. (4) Gasparini, F.; Vogel, P. J. Org. Chem. 1990,55,2451. Reymond, J.-L.; Pinkerton, A. A.; Vogel, P. Ibid. 1991, 56, 2128. Arjona, 0.; de Dios, A.; Fernandkz de la Pradilla, R.; Plumet, J. Tetrahedron Lett. 1991,32,7309. Bimwala, R. M.; Vogel, P. J. Org. Chem. 1992,57,2076. PBchy, P.; Gasparini, F.; Vogel, P. Synlett 1992, 676. Renaud, P.; Vionnet, J.-P. Helu. Chim. Acta 1993, 58, 2490. Arjona, zyxwvutsr 0.; Martin- Domenech, A.; Plumet, J. J. Org. Chem. 1993, 58, 7929. Chen, Y.; Vogel, P. J. Org. Chem. 1994,59, 2487. Vionnet, J.-P.; Renaud, P. Helu. Chim. Acta 1994, 77, 1781. Cossy, J.; Ranaivosta, J.-L.; Bellosta, V. Tetrahedron Lett. 1994, 35, 1205. (5)(a) Schmidt, R. R.; Beitzke, C.; Forrest, A. K. J. Chem. SOC., Chem. Commun. 1982,909. Vieira, E.; Vogel, P. Helv. Chim. Acta 1982, 65, 1700. (b) Black, K. A.; Vogel, P. J. Org. Chem. 1986, 51, 5341. Allemann, S.; Vogel, P. Synthesis 1991, 923. Allemann, S.; Vogel, P. Synlett 1993, 801. Emery, F.; Vogel, P. Ibid. 1995. - 0022-3263/95/1960-8351$09.00/0 (+k4 (4-5 (+)a (4-6 R=(1 S)-camphanoyl R=(l R)camphanoyl at C(2)can be isomerized into the corresponding cyclohex- 4-enols afker deprotonation with an appropriate bases (El,b-like reactions). This type of isomerization can occur with a relatively weak base in the presence of an oxyphilic reagent.g Heterolytic cleavage of the ethereal bridge can be induced with a strong Branstedt or Lewis acid with the participation of a neighboring grouploor of an external nucleophile such as the bromide anion,ll or through a Grob fragmentation.12 Metalhalogen ex- change of 2-halogeno-7-oxabicyclo[2.2. llheptanes can also result in the 7-oxa ring opening.13 7-0xabicyclo[2.2.1]- hept-2-ene derivatives have been reduced into cyclohex- enols through Sp~2 displacements by means of hydrides14 or one-electron transfer processes.15 Alternatively, simi- (6) (a) Clausson-Kaas, E. Acta Chem. Scand. 1952, 6, 560. Cava, M. P.; Wilson, C. L.; Williams, C. J., Jr. J. Am. Chem. SOC. 1956, 78, 2303. Krutak, J. J.; Burpitt, R. D.; Moore, W. H.; Hyatt, J. A. J. Org. Chem. 1979,44, 3847. Hanessian, S.; Beaulieu, P.; Dube, D. Tetrahe- dron Lett. 1986, 27, 5071. Takayama, H.; Hayashi, K.; Koizumi, T. Ibid. 1986,27,5509. Carless, H. A. J.; Oak, 0. Z. J. Chem. SOC., Chem. Commun. 1991, 61. Shchez, A. J.; Konopelski, J. P. Synlett 1994, 335. Schlessinger, R. H.; Pettus, T. R. R.; Springer, J. P.; Hoogsteen, K. J. Org. Chem. 1994, 59, 3246. Sha, C.-K.; Shen, C.-Y.; Lee, R.-S.; Lee, S.-R.; Wang, S.-L. Tetrahedron Lett. 1995, 36, 1283. (b) For the hydrogenolysis of 1-aryl derivatives, see, e.g.: Forsey, S. P.; Rajapaksa, D.; Taylor, N. J.; Rodrigo, R. J. Org. Chem. 1989,54,4280.Pelter, A,; Ward, R. S.; Qianrong, L.; Pis, J. Tetrahedron: Asymmetry 1994, 5, 909. (7) See, e.g., the acid-catalyzed hydrolysis of 7-oxabicyclo- [2.2.l]heptan-2-one: Lajunen, M.; Kaitaranta, E.; Dahlqvist, M. Acta Chem. Scand. 1994,48, 399. 0 1995 American Chemical Society