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PADWA Annulation

PAAL KNORR Pyrrole synthesis 284 PADWA Annulation 285 PAQUETTE Olelination 286 PARHAM Cycle ether synthesis 287 PARNES Gemnal dimethylation 288 Pames 223... [Pg.226]

In an alternative approach to annulation across the indole 2,3-tt system, Padwa and coworkers have reported approaches to the pentacyclic and hexacyclic frameworks of the aspidosperma and kopsifoline alkaloids respectively that involve as the key step a Rh(II)-promoted cyclization-cycloaddition cascade <06OL3275, 06OL5141>. As illustrated in their approach to ( )-aspidophytine 150, Rh2(OAc)4-catalyzed cyclization of a diazo ketoester 148 affords a carbonyl ylide dipole that undergoes [3+2]-cycloaddition across the indole 2,3-tt bond to generate 149 <06OL3275>. [Pg.161]

A convenient method for the synthesis of annulated 2-alkylthio-5-aminofurans has been described by Padwa et al. The reaction sequence involves the formation of a thionium group from readily available dithioacetals upon treatment with dimethyl(methylthio)sulfonium tetrafluoroborate (DMTSF). The thionium ion undergoes cyclization with the 7-carbonyl group followed by an elimination step to yield the 2,3,5-trisubstituted furans in good to excellent yields (Equation 29) <2002JOC1595>. The alkylthioaminofuran reaction products can be utilized to constmct polyclic frameworks of natural products in a subsequent Diels-Alder reaction. [Pg.509]

Padwa and co-workers have reported" that the rhodium(II) acetate catalyzed ring opening of the cyclopropene 75 results in the formation of the bicyclic system 78 of undefined stereochemistry in 52% yield (Scheme 27). It is considered that the reaction occurs by ring opening of 75 to the vinylcarbenoid 76. Cyclization of 76 produces the fiiran 77, which on reaction with a second equivalent of 76 forms the [344] annulation product 78. [Pg.146]


See other pages where PADWA Annulation is mentioned: [Pg.231]    [Pg.23]    [Pg.199]   
See also in sourсe #XX -- [ Pg.285 ]




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