Krzysztof Sienkiewicz - Academia.edu (original) (raw)
Related Authors
Centre National de la Recherche Scientifique / French National Centre for Scientific Research
Uploads
Papers by Krzysztof Sienkiewicz
Tetrahedron Letters, 1994
... 00404039(94)012946 A Concise Synthesis of Two Pyrroles of Marine Origin Charles W. Jefford, K... more ... 00404039(94)012946 A Concise Synthesis of Two Pyrroles of Marine Origin Charles W. Jefford, Krzysztof Sienkiewicz, Steven R. Thornton Department of ... E. Galeazzi, R. Greenhouse, A. Guzman, E. Velarde, Y. Antonio, F. Franco, A. Leon, V. Perez, R.Salas, D. Valdes, J. Ackrell ...
Tetrahedron Letters, 1994
We recently devised a procedure for synthesizing ennntiomerically pure S-substituted and cis-3,5-... more We recently devised a procedure for synthesizing ennntiomerically pure S-substituted and cis-3,5-disubstituted indolizidines from chiml a-amino acids. t** Typically, itI1 acid (1) is converted into its N-pyrrole derivative (3) by condensation with 2,S-dimethoxytetr~hydrofurar~ (2) (Scheme 1). Extension of the side-chain by Amdt-Eistett homologatiou and adjunction of diazomethane affords the a-diazoketone 4 which by catalysis with rhodium acetate closes to the bicyclic pyrrole 5. Formation of the desired diasteteomeric indolizidine 6 is assured by s~ibstit~lent-dinted catalytic liydroget~tiot~ of 5. A logical rn~i~~ation of this sequence is to dispense with homo~ogation by taking a s~iitab~e y-amino acid (7) at the outset and effecting cyclization of the resulting N-py~o~e-btltyric acid 8 to the pyrrofe 9. Catalytic liydro&et~ution, as before, would be expected to give 6. However, previous experiments with aspartic acid and its esters-7.4 indicate that this approach might meet with mitigated success. For example, 2,5-diethoxytetrahydrofuron (2a) reacted poorly with L-aspartic acid (IO), but efficiently with its mono-and diesters 13 and I6 to give the N-pyrrole derivatives 11, 14, and 17 (Scheme 2). Moreover, acid-catalyzed cyclization of I1 to 12 failed entirely whereas the treatment of 14 with phosphorous pentaxide furnished the bicyclic ketone 15 in only 37% yield.
Tetrahedron Letters, 1994
... 00404039(94)012946 A Concise Synthesis of Two Pyrroles of Marine Origin Charles W. Jefford, K... more ... 00404039(94)012946 A Concise Synthesis of Two Pyrroles of Marine Origin Charles W. Jefford, Krzysztof Sienkiewicz, Steven R. Thornton Department of ... E. Galeazzi, R. Greenhouse, A. Guzman, E. Velarde, Y. Antonio, F. Franco, A. Leon, V. Perez, R.Salas, D. Valdes, J. Ackrell ...
Tetrahedron Letters, 1994
We recently devised a procedure for synthesizing ennntiomerically pure S-substituted and cis-3,5-... more We recently devised a procedure for synthesizing ennntiomerically pure S-substituted and cis-3,5-disubstituted indolizidines from chiml a-amino acids. t** Typically, itI1 acid (1) is converted into its N-pyrrole derivative (3) by condensation with 2,S-dimethoxytetr~hydrofurar~ (2) (Scheme 1). Extension of the side-chain by Amdt-Eistett homologatiou and adjunction of diazomethane affords the a-diazoketone 4 which by catalysis with rhodium acetate closes to the bicyclic pyrrole 5. Formation of the desired diasteteomeric indolizidine 6 is assured by s~ibstit~lent-dinted catalytic liydroget~tiot~ of 5. A logical rn~i~~ation of this sequence is to dispense with homo~ogation by taking a s~iitab~e y-amino acid (7) at the outset and effecting cyclization of the resulting N-py~o~e-btltyric acid 8 to the pyrrofe 9. Catalytic liydro&et~ution, as before, would be expected to give 6. However, previous experiments with aspartic acid and its esters-7.4 indicate that this approach might meet with mitigated success. For example, 2,5-diethoxytetrahydrofuron (2a) reacted poorly with L-aspartic acid (IO), but efficiently with its mono-and diesters 13 and I6 to give the N-pyrrole derivatives 11, 14, and 17 (Scheme 2). Moreover, acid-catalyzed cyclization of I1 to 12 failed entirely whereas the treatment of 14 with phosphorous pentaxide furnished the bicyclic ketone 15 in only 37% yield.