“…With the carboxylic acid 9 in hand, the cyclization reaction promoted by different silver salts was studied. 19 Silver trifluoroacetate 20 led only to the loss of the trityl group. Adding Na2CO3 to the silver trifluoroacetate to buffer the reaction did not lead to product either.…”
N-Glycinamide oxazolidinones are key intermediates for the synthesis of a new class of peptidomimetics. We report, herein, the synthesis of a series of 3,4,5-trisubstituted oxazolidinones with a glycine residue at N-3 of the oxazolidinone ring. Substituents at C-4 and C-5 contain substitution capabilities which are amenable for the introduction of additional peptide chains. The synthesis of the key N-Glycinamide oxazolidinone is made possible through two reactions; a tandem aziridine ring opening/oxazolidinone alkylation and, subsequently, a fused-lactone ring opening by an amine which leads to the N-Glycinamide oxazolidinones.
“…With the carboxylic acid 9 in hand, the cyclization reaction promoted by different silver salts was studied. 19 Silver trifluoroacetate 20 led only to the loss of the trityl group. Adding Na2CO3 to the silver trifluoroacetate to buffer the reaction did not lead to product either.…”
N-Glycinamide oxazolidinones are key intermediates for the synthesis of a new class of peptidomimetics. We report, herein, the synthesis of a series of 3,4,5-trisubstituted oxazolidinones with a glycine residue at N-3 of the oxazolidinone ring. Substituents at C-4 and C-5 contain substitution capabilities which are amenable for the introduction of additional peptide chains. The synthesis of the key N-Glycinamide oxazolidinone is made possible through two reactions; a tandem aziridine ring opening/oxazolidinone alkylation and, subsequently, a fused-lactone ring opening by an amine which leads to the N-Glycinamide oxazolidinones.
“…Starting from diastereomerically pure (4 S *,5 R *)‐ 25 , the reaction with trimethylsilyl triflate (TMSOTf) at low temperature furnished the enol ether 26 in almost quantitative yield (Scheme ). Treatment with methyl iodide in the presence of silver salts as activating agents22 led to the desired product 27 in 62 % yield (99 % based on 37 % re‐isolated 25 ) with a diastereomeric ratio of 86:14. The preferred formation of one diastereomer, which later on was assigned to have a 4 S *,5 R *,9 S * configuration based on the X‐ray structure analysis of a succeeding product, must be caused by kinetic control, as erosion of the diastereomeric ratio was observed when 27 was stored in [D 4 ]MeOH in the presence of a catalytic amount of sodium methoxide.…”
To elucidate the structure of the new natural product spirodionic acid, which has three stereogenic centers of hitherto unknown configuration, two 4-ethenylspiro[4.5]dec-6-en-1,8-diones with opposite relative configuration at C4 and C5 were prepared. The first access involved the synthesis of 3-ethenyl-2-formylcyclopentanone (8) using a three-component coupling process. A sequence of Michael addition to penten-3-one (7) and intramolecular aldol condensation then led to the highly selective formation of the 4S*,5S*-configured spirocycle 5. In contrast, a selective spiroannelation of a cyclohexenone ring was accomplished by a novel type of twofold Michael addition to the dialkenyl ketone 11 with subsequent dehydrogenation to furnish the 4S*,5R*-configured spirocycle 25. Diastereoselective methylation and oxidative degradation then completed a highly efficient synthesis of the natural product as prerequisite for the assignment of its absolute configuration.
“…Treatment of α-methyl ketone 9 with potassium hydride and tert -butyldimethylsilyl chloride provided the thermodynamic silyl enol ether with high regioselectivity. Introduction of the allyl group was achieved via a silver trifluoroacetate-mediated allylation using allyl iodide . Subsequently, the primary hydroxyl functionality was formed through a chemoselective hydroboration of the terminal alkene with dicyclohexylborane in the presence of the trisubstituted double bond and the ketone providing compound 5 . , 2 Initial Steps of the Synthesis…”
An efficient synthesis of the cladiellin skeleton is reported utilizing methods that were previously developed in this laboratory. The approach is based on a SmI(2)-mediated cyclization reaction for the construction of the oxacyclononane unit. A [4 + 3] annulation strategy was used to create the octahydroisobenzofuran moiety. This route provides the cladiellin skeleton in only 14 steps without the use of protecting groups. The present approach also enabled the synthesis of the 3,7-diastereomer of the natural product polyanthellin A.
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