Utility and NMR studies of α,β-unsaturated acylammonium salts: synthesis of polycyclic dihydropyranones and a dihydropyridone

Abstract

Please cite this article as: Vellalath, S., Van, K.N., Romo, D., Utility and NMR studies of α,β-unsaturated acylammonium salts: Synthesis of polycyclic dihydropyranones and a dihydropyridone, Tetrahedron Letters (2015), doi: http://dx.

Asymmetric Organocatalysis: The Emerging Utility of α,β‐Unsaturated Acylammonium Salts

“…In an extension of their previous studies and of early studies by Yamamura et al., the group of Romo reported the synthesis of polycyclic dihydropyranones from commodity acid chlorides and cyclic 1,3‐dicarbonyl compounds with DMAP as Lewis base promoter (Scheme ) . An of excess (2.0 equiv) cyclic β‐diketones and prolonged reaction times were critical for optimal yields and this was attributed to the reversible formation of the enol ester by‐product 56 through O‐acylation; by performing crossover experiments, 56 was shown to slowly re‐enter the catalytic cycle.…”

“…20 The use of excess (2.0 equiv) cyclic-β-diketones and prolonged reaction times were critical for optimal yields and this was attributed to the reversible formation of an enol ester by-product 56 formed through O -acylation which was shown to re-enter the catalytic cycle but only slowly through cross-over experiments. Under optimized conditions, crotonyl chloride 1 and hydroxycoumarin 52 with DMAP as Lewis base promoter, provided enol-lactone 53 in good yield.…”

Chemoselectivity in Esterification Reactions – Size Matters after All

“…Figure 3 shows the spectra obtained with benzoyl chloride (2a) (spectrum IV) in comparison to those for pure TCAP (4) (spectrum III), TCAP•HCl (spectrum II), and the corresponding pyridinium carboxylate (spectrum I). Analysis of these spectra allows for the following conclusions: 1) TCAP and benzoyl chloride react quantitatively under formation of two adducts in a ratio of 70:30 (spectrum IV); 2) The signals for the major component correspond to acylpyridinium ion S3 due to the large shifts downfield compared to pure TCAP (spectra III, IV); 13 3) These large shifts of the aromatic proton peak (7.8 → 8.1 ppm) and the aliphatic ones (especially the one from 3.2 to 3.8 ppm) are presumably caused by the rehybridization of the nitrogen atoms in the TCAP/acid chloride adduct (spectra III, IV); 4)…”

Stereodivergent, Diels–Alder-initiated organocascades employing α,β-unsaturated acylammonium salts: scope, mechanism, and application

“…64 We therefore performed a 1 H– 13 C gHMQC experiment and measured the 13 C NMR chemical shifts in CD 2 Cl 2 at 23 °C for the acylammonium salt 17 formed through chloride ion exchange reaction of the acid chloride 5 with the Lewis base, ( S )-(–)-BTM (Fig. 5c).…”