@article { ISI:000294656400011, title = {One-step stereospecific strategy for the construction of the core structure of the 5,11-methanomorphanthridine alkaloids in racemic as well as in optically pure form: synthesis of (+/-)-pancracine and (+/-)-brunsvigine}, journal = {European Journal of Organic Chemistry}, number = {24}, year = {2011}, month = {AUG}, pages = {4571-4587}, publisher = {WILEY-V C H VERLAG GMBH}, address = {PO BOX 10 11 61, D-69451 WEINHEIM, GERMANY}, abstract = {

The unique core structure of the complex pentacyclic 5,11-methanomorphanthridine has been constructed stereospecifically in one step by an intramolecular [3+2] cycloaddition of a non-stabilized azomethine ylide (AMY), generated by the sequential double desilylation of 14 using (AgF)-F-I as a one-electron oxidant. The formation of the single diastereomer in the key step is explained by the preferred transition state produced by endo attack of the AMY on the {\textquoteleft}{\textquoteleft}Re{\textquoteright}{\textquoteright} face of the dipolarophile. An asymmetric version of the cycloaddition using a chiral dipolarophile was applied to construct the core structure 68 with 63 \% ee. This strategy was successfully applied to the formal synthesis of (+/-)-pancracine and the total synthesis of (+/-)-brunsvigine. An unprecedented and interesting skeletal rearrangement product 49 was observed during the attempted assembly of the E ring from 46 through Horner-Wadsworth-Emmons reactions. Mechanisms involving azetidinium salt formation or the Grob-type fragmentation are advanced to explain the observed rearrangement.

}, keywords = {alkaloids, Azomethine ylides, Cycloaddition, Ring-closing metathesis, synthesis design}, issn = {1434-193X}, doi = {10.1002/ejoc.201100601}, author = {Pandey, Ganesh and Kumar, Ravindra and Banerjee, Prabal and Puranik, Vedavati G.} }