The key THF derivative (9a) for an enantioselective synthesis of amphidinolide X/Y was obtained from 1a via a selenoetherification reaction. In fact, among the cyclization methods investigated, the highest yield and stereocontrol were achieved at -78 degrees C with PhSeCl/EtiPr2N from diols 1a (anti-Z) and 1b (anti-E) and with PhSeCl/ZnBr2 from diols 1c (syn-Z) and 1d (syn-E). Also, surprisingly, use of protecting groups (on the allylic OH) was detrimental in the cases studied. The diverse THF-tetrasubstituted stereoisomers will provide a series of amphidinolide X/Y analogues. [structure: see text]
The conjugate additions of titanium enolates of glycolate-derived chiral oxazolidin-2-ones to various Michael acceptors have been evaluated as an entry to enantiopure 1,2,5-trioxygenated and related synthons. alpha,beta-unsaturated Weinreb and morpholine amides do react under suitable conditions and their adducts can be converted to diverse C1-C5 chiral fragments.
The TiCl 3 (O-iPr)-mediated addition of the amides (II) to the oxazolidinone (I) allows access to the polyoxygenated products (III) with excellent enantioselectivity. These compounds are able to undergo chemoselective reduction yielding the alcohols (IV) or the aldehydes (V) which are important building blocks. -(OLIVELLA, A.; RODRIGUEZ-ESCRICH, C.; URPI*, F.; VILARRASA, J.; J. Org. Chem. 73 (2008) 4, 1578-1581; Dep. Quim. Org., Fac. Quim., Univ. Barcelona, E-08028 Barcelona, Spain; Eng.) -Jannicke 25-048
Synthesis of Amphidinolide Y Precursors. -A new synthesis of the open precursors of the title compound is presented. The final metathesis reaction requires large amounts of the Hoveyda-Grubbs II catalyst for complete conversion. -(MOLA, L.; OLIVELLA, A.; URPI*, F.; VILARRASA, J.; Tetrahedron Lett. 55 (2014) 4, 900-902, http://dx.
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