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Denmark, Scott E. Thorarensen, Atli 2011-05-07T12:24:17Z 2011-05-07T12:24:17Z 10000-01-01 1996 A short and efficient asymmetric synthesis of the pyrrolizidine necine base (${-}$)-hastanecine is described. The key reaction in the synthesis is a sequential inter (4+2) /inter (3+2) cycloaddition. The Lewis acid promoted (4+2) cycloaddition between 2-acyloxy nitroalkene 90 and chiral vinyl ether (+)-28 afforded a nitronate which underwent facile (3+2) cycloaddition with dimethyl maleate. The resulting nitroso acetal (${-}$)-96 had all the required stereocenters for (${-}$)-hastanecine. The critical unmasking of the nitroso acetal (${-}$)-96 employed a hydrogenolytic cleavage to give the 1-azabicyclo (3.3.0) octane skeleton of (${-}$)-hastanecine. (${-}$)-Rosmarinecine 42 is the necine base portion of the pyrrolizidine alkaloid (${-}$)-rosmarinine. (${-}$)-Rosmarinecine is a representative of that group of pyrrolizidines which bear a cis relationship between adjacent stereocenters C(1), C(7) and C(7a) in addition to a highly oxygenated skeleton. (${-}$)-Rosmarinecine has been synthesized in 8 steps and 14.8% overall yield, as an illustration of a general approach for the construction of pyrrolizidines bearing this stereochemical feature. The key step in the asymmetric synthesis is a Lewis acid-promoted, tandem inter (4+2) /intra (3+2) cycloaddition between a fumaroyloxynitroalkene 165 and a chiral vinyl ether (${-}$)-29. Numerous alkaloids contain (+)-crotanecine 36 as it necine constituent. (+)-Crotanecine which is an all cis substituted necine has been prepared in 10 steps and 10.2% overall yield. The key steps in the asymmetric synthesis is a Lewis acid-promoted, tandem inter (4+2) /intra (3+2) cycloaddition between a fumaroyloxynitroalkene 165 and a chiral propenyl ether (${-}$)-222 and a solvolytic elimination of a mesylate to install the unsaturation at C(6)-C(7). Made available in DSpace on 2011-05-07T12:24:17Z (GMT). No. of bitstreams: 2 license.txt: 4922 bytes, checksum: 910b249b4beec47e7ab768910c8f966f (MD5) 9712459.pdf: 11700756 bytes, checksum: ee60140bbcc9a76d78ad527a16169fc5 (MD5) Previous issue date: 1996 Item marked as restricted to the 'UIUC Users [automated]' Group (id=2) by Howard Ding (hding2@illinois.edu) on 2011-05-07T14:40:36Z Item is restricted indefinitely. Restriction data tranferred 2014-07-01T11:17:26-05:00 Original Data Group with Access UIUC Users [automated] Release Date: none Reason: ETDs are only available to UIUC Users without author permission ETDs are only available to UIUC Users without author permission U of I Only 9780591199413 AAI9712459 (UMI)AAI9712459 http://hdl.handle.net/2142/19961 eng Copyright 1996 Thorarensen, Atli Chemistry, Organic The total syntheses of (+)-crotanecine, (-)-hastanecine and (-)-rosmarinecine utilizing the tandem (4+2)/(3+2) cycloadditions of nitroalkenes text Chemistry, Organic Chemistry, Organic University of Illinois at Urbana-Champaign Dissertation Ph.D.