Optically Active Cyclobutanone Chemistry: Synthesis of (−)-Cyclobut-A and (±)-3‘-Epi-Cyclobut-A
摘要:
The carbocyclic nucleoside analogues (-)-cyclobut-A and (+/-)-3'-epi-cyclobut-A were synthesized utilizing photolysis of the (benzyloxymethyl)(methoxy) chromium carbene complex 4 with optically active ene-carbamate 5 to produce the corresponding optically active alpha,alpha-disubstituted cyclobutanone 6. Stereoselective removal of the alpha-ethoxy group with inversion gave cyclobutanone 7, which was converted by existing methodology to the title compounds.
Synthesis of N-Vinyloxazolidinones and Morpholines from Amino Alcohols and Vinylsulfonium Salts: Analysis of the Outcome's Dependence on the N-Protecting Group by Nanospray Mass Spectrometry
作者:Muhammad Yar、Sven P. Fritz、Paul J. Gates、Eoghan M. McGarrigle、Varinder K. Aggarwal
DOI:10.1002/ejoc.201101272
日期:2012.1
in annulation reactions with diphenylvinylsulfonium triflate has been investigated. Although tosyl and sulfinamide groups give morpholines in high yields, the use of N-Cbz leads to a high-yielding synthesis of N-vinyloxazolidinones. The reactions were monitored by nanospray MS/MS, which revealed why reactions are successful and the fate of reactive intermediates in the unsuccessful reactions.
The title synthesis was achieved by featuring diastereoface selective cyclopropanation of (4R,5S)-4,5-diphenyl-3-vinyl-2-oxazolidinone, the chiral and conformationally rigid N-vinylcarbamate, with zinc-monofluorocarbenoid followed by hydrogenolysis of formed (4R,5S)-3-[(1R-2S)-2-fluorocyclopropyl]-4,5-diphenyl-2-oxalidinone.
Chiral enamides 5f–i were found to react with pyrylium ylides to give cycloadducts 6d–i in good yields with an excellent level of stereoselectivity. The chiral auxiliary was successfully removed on hydrogenolysis of compound 6f in continuous flow (H-Cube) resulting in the first asymmetric synthesis of complex amine 8.
De Novo Synthesis of 4‘-Ethoxy Nucleoside Analogues
作者:Louis S. Hegedus、Lisa Geisler、Andrew G. Riches、Sarri S. Salman、Gisela Umbricht
DOI:10.1021/jo020151f
日期:2002.11.1
Butenolides 5a and 13 were used as opticallyactive templates in the de novo synthesis of 4'-disubstituted nucleoside analogues. The butenolides were reduced and acylated in situ to give acetates 10 and 14. Vorbrüggen coupling gave the protected nucleoside analogues 11 and 15. Reduction of 11 gave 4'-ethoxy-2',3'-dideoxythymidine (6) and deprotection of 15 gave 4'-ethoxy-2',3'-dideoxydidehydrothymidine