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Denmark, Scott E. Schnute, Mark Edward 2011-05-07T13:38:43Z 2011-05-07T13:38:43Z 10000-01-01 1995 Chiral enol ether dienophiles derived from (1R,2S)-($-$)-2-phenylcyclohexanol and (R)-($-$)-2,2-diphenylcyclopentanol (($-$)-6 have been found to provide high levels of asymmetric induction in tandem inter (4+2) /intra (3+2) nitroalkene cycloadditions. Either enantiomeric series of tandem cycloaddition/hydrogenolysis product is available from the chiral auxiliary of a single absolute configuration by judicious selection of the Lewis acid promoter, Ti(Oi-Pr)$\sb{2}$Cl$\sb{2}$ (98% ee, ($-$)) or methylaluminum bis-(2,6-diphenylphenoxide) (MAPh) (93% ee, (+)). Propenyl ethers derived from ($-$)-6 undergo endo-selective (4+2) cycloadditions (2.3/1-8.2/1) in the presence Ti(Oi-Pr)$\sb2$Cl$\sb2$, however, exoselective (4+2) cycloadditions (10.2/l-54.8/l) are observed in the presence of MAPh. 2-(Acyloxy)vinyl ethers undergo regioselective (4+2) cycloadditions with nitroalkenes (promoted by SnCl$\sb4$) to afford substituted 5-acetoxy nitronates in good yields (68%-91%). The endo/exo selectivity in the cycloadditions has been found to be dependent on the nitroalkene substitution; 2-aryl-1-nitroalkenes provided exclusively exo cycloadducts while 2-cyclohexyl-1-nitroethene afforded predominately endo cycloadducts (12/1). The resulting nitronates can be elaborated to N-tosyl-4-substituted-3-hydroxypyrrolidines by hydrogenolysis (160 psi of H$\sb2$/PtO$\sb2$) or to bicyclic $\alpha$-hydroxy lactams by (3+2) cycloaddition followed by hydrogenation (14.7 psi of H$\sb2$/Raney nickel). A chiral 2-acetoxyvinyl ether derived from ($-$)-6 has been employed in the cycloaddition-hydrogenation sequence to prepare an optically active N-tosyl-3-hydroxypyrrolidine in high enantiomeric excess (96% ee). The strategy of nitroalkene (4+2) cycloadditions employing 2-acetoxyvinyl ethers as dienophiles has been explored toward the total synthesis of the Amaryllidaceae alkaloid (+)-pretazettine. Made available in DSpace on 2011-05-07T13:38:43Z (GMT). No. of bitstreams: 2 license.txt: 4922 bytes, checksum: 910b249b4beec47e7ab768910c8f966f (MD5) 9543716.pdf: 17055410 bytes, checksum: bb07202659ccf6f30889b6e5747a3fd2 (MD5) Previous issue date: 1995 Item marked as restricted to the 'UIUC Users [automated]' Group (id=2) by Howard Ding (hding2@illinois.edu) on 2011-05-07T14:57:23Z Item is restricted indefinitely. Restriction data tranferred 2014-07-01T11:26:54-05:00 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 AAI9543716 (UMI)AAI9543716 http://hdl.handle.net/2142/22403 eng Copyright 1995 Schnute, Mark Edward Chemistry, Organic Nitroalkene (4+2) cycloadditions of achiral and chiral vinyl ethers. The stereochemical consequence of the Lewis acid promoter and studies toward the total synthesis of (+)-pretazettine text Chemistry Chemistry University of Illinois at Urbana-Champaign Dissertation Ph.D.