02060nas a2200229   4500008004100000022001400041245022300055210006900278260007700347300001400424520107400438653001401512653002201526653001801548653002801566653002101594100001901615700002001634700002101654700002601675856012901701       2011                        eng d  a1434-193X00aOne-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 (+/-)-brunsvigine0 aOnestep stereospecific strategy for the construction of the core  aPO BOX 10 11 61, D-69451 WEINHEIM, GERMANYbWILEY-V C H VERLAG GMBHcAUG  a4571-45873 a<p>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 ``Re'' 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.</p>10aalkaloids10aAzomethine ylides10aCycloaddition10aRing-closing metathesis10asynthesis design1 aPandey, Ganesh1 aKumar, Ravindra1 aBanerjee, Prabal1 aPuranik, Vedavati, G.  uhttps://library.ncl.res.in/content/one-step-stereospecific-strategy-construction-core-structure-511-methanomorphanthridine-0