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Ring closure reactions
Ring closure reactions O 0130Stereoselective Palladium-Catalyzed Carbocyclization of Allenic Allylic Carboxylates. -The palladium-catalyzed cyclization of various allenes tethered to cyclohexene or cycloheptene rings is studied. The cis-carboxylates (I), (IV), (IX) and (XIV) are smoothly converted to the corresponding cis-fused bicyclic compounds (II), (V), (X) and (XV), resp., and the best results are obtained for benzoates [cf. (IVa) vs. (I)]. The cyclization of the corresponding trans-carboxylates (XVII) and (XX) can be controlled by the reaction conditions. Thus, cyclization of derivatives (XVII) in apolar solvent (toluene or decane) provides access towards trans-fused bicyclics (XVIII) while the corresponding cis-isomers are formed in the polar solvent acetonitrile. -(FRANZEN, J.; LOEFSTEDT, J.; FALK, J.; BAECKVALL*, J.-E.; J. Am. Chem. Soc. 125 (2003) 46, 14140-14148; Dep. Org. Chem., Arrhenius Lab., Univ. Stockholm, S-106 91 Stockholm, Swed.; Eng.) -Mischke 11-043 2004 Ring closure reactions
1997 stereochemistry stereochemistry (general, optical resolution) O 0030 31 -053 Stereoselective Intermolecular Oxymercurations of Allylic Ethers. -The regioselectivity is complete in all reactions investigated; the diastereoselectivity depends on the alkene geometry and the substitution pattern. The results may be of interest for the preparation of polyoxygenated molecules. -(CORMICK, R.; LOEFSTEDT, J.; PERLMUTTER, P.; WESTMAN, G.; Tetrahedron Lett. 38 (1997) 15,
Ring closure reactions
Ring closure reactions O 0130Palladium-Catalyzed Carbocyclization of Allene-Diene Derivatives. Exploring Different Nucleophiles. -An improved method for the palladium-catalyzed nucleophilic substitution-intramolecular carbocyclization of allene-diene derivatives (I) and (V) is presented. The reactions can be performed in organic solvents like dichloromethane or acetone which allows for reduction of the amount of nucleophile to 10 equivalents and broadens the range of nucleophiles applicable. Interestingly, carbocyclization of allenylcycloheptadiene (V) proceeds with exclusive trans-selectivity, while the corresponding allenylcyclohexadiene (I) cyclizes with absolute cis-selectivity. The ratio of 1,2-to 1,4-addition products in the reaction of cycloheptadiene derivative (V) strongly depends on the nature of nucleophile. -(LOEFSTEDT, J.; NAERHI, K.; DORANGE, I.; BAECKVALL*, J.-E.; J. Org. Chem. 68 (2003) 19, 7243-7248; Dep. Org. Chem., Arrhenius Lab., Univ. Stockholm, S-106 91 Stockholm, Swed.; Eng.) -Mischke 07-048 2004 Ring closure reactions
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