2009
DOI: 10.1002/ejoc.200900114
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A Single‐Step Synthesis of 4‐Oxazolin‐2‐ones and Their Use in the Construction of Polycyclic Structures Bearing Quaternary Stereocenters

Abstract: A new method for the synthesis of 4-oxazolin-2-ones by a one-pot MW-promoted condensation of α-ketols and isocyanates is reported. An alternative thermal approach using the same starting materials is also described. These cyclic enamides were efficient nucleophiles, reacting with Michael acceptors and prenyl bromide to give a variety of polycyclic

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Cited by 20 publications
(30 citation statements)
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“…As expected, when 4‐oxazolin‐2‐ones 1a‐b were submitted to more severe conditions in the presence of the same Michael acceptors 8a‐b , and with methyl iodide as the promoting agent, mixtures of dihydrobenzo[ d ]oxazol‐2(3 H )‐ones 33a‐e / 34a‐e were generated (Table ). The diastereoselectivity was lower than that of the fused tetrahydro‐2 H ‐pyrano[2,3‐ d ]oxazol‐2‐ones 29 / 30 , presumably because of the higher temperature applied.…”
Section: Resultssupporting
confidence: 63%
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“…As expected, when 4‐oxazolin‐2‐ones 1a‐b were submitted to more severe conditions in the presence of the same Michael acceptors 8a‐b , and with methyl iodide as the promoting agent, mixtures of dihydrobenzo[ d ]oxazol‐2(3 H )‐ones 33a‐e / 34a‐e were generated (Table ). The diastereoselectivity was lower than that of the fused tetrahydro‐2 H ‐pyrano[2,3‐ d ]oxazol‐2‐ones 29 / 30 , presumably because of the higher temperature applied.…”
Section: Resultssupporting
confidence: 63%
“…On the basis of the previously developed regioselective synthesis of N ‐substituted 4‐oxazolin‐2‐ones 1 and 4‐methylene‐2‐oxazolidinones 2 , resulting from the condensation of α‐ketol 3a and isocyanates 4 (Scheme ), in a preliminary report, we presented the one‐pot synthesis of the optically pure version of heterocycles 1‐2 by introducing the N ‐( S )‐methylbenzyl moiety as the chiral auxiliary . Although this methodology was also efficient for the preparation of the corresponding 3‐substituted 4‐oxazolin‐2‐thiones 6 and 4‐methylene‐1,3‐oxazolidin‐2‐thiones 7 , these heterocycles were not able to undergo further reactions when utilizing the thioenamide functionality as a nucleophile . In contrast, compounds 1 behave as an enolate equivalent in the presence of a Michael acceptor, in which the regioselectivity was totally controlled by the enamide moiety, leading to the addition product at C‐5 of compound 9 ( R 2 = Me).…”
Section: Introductionmentioning
confidence: 99%
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“…16,17 More recent publications show that this condensation towards open chain carbamates or cyclic hemiaminals (anti and syn adducts) and dehydrated exo-and endo-adducts is thermodynamically controlled. 13,18 The addition of bifunctional isocyanates (hexamethylene diisocyanate and toluene 2,4-diisocyanate) has also been evaluated (Scheme 2). For the aliphatic diisocyanate, the reaction was complete after 5 hours of reflux in 1,2-dichloroethane.…”
Section: Resultsmentioning
confidence: 99%
“…The generality and scope of this dimerization reaction was explored and the results are shown in Table . Thus, a series of N ‐substituted (alkyl, allyl, benzyl and aryl) 2‐oxazolones ( 1 a – l ) prepared according to known procedures (see Supporting Information for details) were subjected to the optimized conditions [BF 3 ⋅Et 2 O (0.5 equiv), with or without addition of H 2 O (see below for further discussion), CH 2 Cl 2 , 25–50 °C] to afford (racemic) dimeric products 2 a – l in excellent yields. It is worth noting that substrates with N ‐aryl groups (entries 7–11, Table ) underwent the dimerization more rapidly and at lower temperature (25 °C) than the N ‐alkyl substrates (entries 1–6 and 12, Table ) (ca.…”
Section: Methodsmentioning
confidence: 99%