@article { ISI:000287163000011, title = {Construction of the 5,10b-phenanthridine skeleton using [3+2]-cycloaddition of a non-stabilized azomethine ylide: total synthesis of (+/-)-maritidine and (+/-)-crinine alkaloids}, journal = {European Journal of Organic Chemistry}, number = {4}, year = {2011}, month = {FEB}, pages = {740-750}, publisher = {WILEY-V C H VERLAG GMBH}, address = {PO BOX 10 11 61, D-69451 WEINHEIM, GERMANY}, abstract = {

Vicinal quaternary and tertiary stereocenters of the 5,10b-phenanthridine skeleton 1 are constructed simultaneously in one step by the [3+2]-cycloaddition of non-stabilized azomethine ylide 9, generated by sequential double desilylation of 10 utilizing silver(I) fluoride as a one-electron oxidant. The regioas well as stereochemical origin of this cycloaddition reaction is explained through a favorable transition state 9{\textquoteright}{\textquoteright}. The strategy is successfully applied for the total synthesis of the biologically active alkaloids (+/-)-maritidine (1a), (+/-)-crinine (1b), and their analogues (1d, 1e, and 1f).

}, keywords = {alkaloids, Azomethine ylides, Cycloaddition, Natural products, Ylides}, issn = {1434-193X}, doi = {10.1002/ejoc.201001263}, author = {Pandey, Ganesh and Gupta, Nishant R. and Gadre, Smita R.} } @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.} } @article {46849, title = {Synthesis of 2-azabicyclo[m.n.0]-alkanes and their application towards the synthesis of strychnos and stemona classes of alkaloids}, journal = {European Journal of Organic Chemistry}, volume = {2020}, year = {2020}, month = {JUL }, pages = {3883-3888}, type = {Article}, abstract = {

2-Azabicyclo[m.n.0]alkane ring systems, the conceptual precursors towards the synthesis of Strychnos and Stemona classes of alkaloids, were synthesized from tert-butyl 2-(phenylsulfonyl)-7-aza-bicyclo[2.2.1]hept-2-ene-7-carboxylate by alkyl Grignard reaction and intramolecular cyclisation of the in situ generated ring opening product 2. The synthesized cis-hexahydroindole 3 and cis-octahydro-benzo[b]azepine 5 scaffolds were utilized to construct the advanced intermediates 25 and 35, respectively, towards the synthesis of the corresponding Strychnos and Stemona classes of alkaloids.

}, keywords = {alkaloids, amines, Grignard reaction, Michael addition, Natural products}, issn = {1434-193X}, doi = {10.1002/ejoc.202000507, Early Access Date = MAY 2020}, author = {Majumder, Binoy and Pandey, Ganesh} }