An intramolecular oxa-Michael reaction on α,β-unsaturated α-amino-δ-hydroxycarboxylic acid esters. Synthesis of functionalized 1,3-dioxanes

Abstract

A highly diastereoselective intramolecular oxa-Michael reaction on α,β-unsaturated α-amino-δ-hydroxycarboxylic acid esters is presented; 1,3-dioxanes functionalized in positions 2,4 and 6 were obtained in good yields and with excellent selectivities; an experimental and computational study was carried out to understand the reaction course in terms of yields and selectivities. This reaction proceeds under mild reaction conditions using highly electrophilic aldehydes and ketones.

Matched/Mismatched Cases in Proline-Catalyzed Cascade Reactions with Carbohydrates: A Computational Insight into the Role of d- and l-Proline

“…Transition states could not be located during these calculations due to the high reactivity of the deprotonated intermediate X . This fact is in accordance with results which were obtained by computational studies of intramolecular oxa-Michael reactions reported by Miscione and Gamba-Sanchez …”

“…This fact is in accordance with results which were obtained by computational studies of intramolecular oxa-Michael reactions reported by Miscione and Gamba-Sanchez. 22 The configurative result of calculations of this intramolecular oxa-Michael reaction (α-configured intermediates XI and XII) is consistent (in accordance) with the findings observed and calculated by Taylor et al 23 The initially formed "cis"-furan (nomenclature of configuration by Taylor is identical with αconfiguration of intermediates XI and XII in this article) can undergo a base-catalyzed thermodynamic equilibration by a retro-Michael reaction to yield the "trans"-furan (β-configured intermediates XI and XII). These conclusions are supported by the results that were obtained by cascade reactions of aldopentoses with methyl ketones.…”

Unprecedented Water Effect as a Key Element in Salicyl-Glycine Schiff Base Synthesis

“…To clarify the above observations, we hypothesized that trace amounts of water present in methanol led to the desired product, whereas an excess of water led to hydrolysis and, in its absence, other, different side reactions occurred. It is probable that under these anhydrous conditions, as the next step of condensation, the resulting ligand reacts with salicylaldehyde in an oxo-Michael reaction to form a chromanone derivative which can further react with compounds present in the mixture (Scheme 4) [28][29][30][31][32]. Additionally, we performed experimental studies on the thermal stability of both forms 1a and 1b in their solid states and the reversibility of their transformation to each other.…”

Synthesis of 1,3-Diols by O-Nucleophile Additions to Activated Alkenes

“…The 1-amino-2,4-diol motif is commonly found in natural products. When Gamba-Sánchez, Miscione, and coworkers treated conjugated esters with a protected α-amino group with excess aromatic aldehyde and t-BuOK in order to synthesize such a motif, 18 there was a definite trend: electron-poor aromatic aldehydes gave better conversion [Scheme 9 (b)]. 19 They then optimized this reaction and found that LiHMDS was the best base for this transformation [Scheme 10 (a)].…”