Investigation of oxidopyrylium–alkene [5+2] cycloaddition conjugate addition cascade (C³) sequences

Abstract

Novel oxidopyrylium-alkene [5+2] cycloaddition conjugate addition cascade (C(3)) sequences are described. Various acetoxypyranone-alkenes with pendant nucleophiles undergo [5+2] cycloaddition followed by conjugate addition from the concave face of the intermediate pyranone toward bridged, tetracyclic ethers. In several cases, 3 new rings, 4 new bonds, and 6 new contiguous stereocenters are constructed with excellent diastereoselectivity. Finally, an asynchronous concerted reaction pathway is proposed to explain the high diastereoselectivity of the oxidopyrylium-alkene [5+2] C(3).

Fingerprinting the Nature of Anions in Pyrylium Complexes: Dual Binding Mode for Anion–π Interactions

“…All synthesized compounds showedas inglet assigned to H-3/H-5 protons in the range of d = 9.06 to 8.98 ppm (for compounds 3 and 17,r espectively). Fluorine-containinga nions (compounds 9, 10,a nd 11)w ere also characterizedb yu sing 19 FNMR spectroscopy.F or example, the 19 FNMR spectrum of compound 10 displayed ad oublet (J = 711Hz) at d = À70.23 ppm, which thus corroborated the anion nature.…”

“…Thus, compound 3 (X:C l À )s hows Dd values of 4. 19 F-1 HH OESY experiment in which intermolecular 19 F-1 HN OEs with these protons were observed even in DMSO (Figure 7). [28] Finally,e xperimental evidences uggests that both the geometricalf eaturesa nd also the nature of atom, which is in direct contact with the H-3/H-5 protons, significantly influence the chemical shifts.…”

“…[D 6 ]acetone and [D 6 ]DMSO that contained 1% TMS were used as the solvents for 4 and 20 mm concentrations, respectively.F or characterization purposes, 1 H, 13 C, 19 F, and 31 PNMR spectra were only acquired in [D 6 ]DMSO. The 19 Fc hemical shifts were referenced indirectly to CCl 3 F( X = 94.094011), whereas 31 Pc hemical shifts were referenced to H 3 PO 4 (X = 40.480742). [29] Selective 1D 19 F-1 HH OESY spectra [30] were measured at 303 Kw ith an optimal mixing time of 1.2 s.…”

“…[18] Moreover,t hese systems have recently been involved as intermediates in transition metal-catalyzed cycloadditions due to the high reactivity of the pyrylium cation. [19] It is known that in anion-p contacts the natureo ft he anion plays as ignificant role that involves changes in polarization. Indeed, the size of the anion affects the arene···anione quilibrium distance and, therefore, modifies the interaction energy.…”

The chemistry of the carbon-transition metal double and triple bond: Annual survey covering the year 2014

“…Several papers report on the cross metathesis of inexpensive low molecular weight α,β-unsaturated carbonyl compounds with other more precious alkenes, including cross metatheses of: (1) acrolein with a 22-carbon α,ω-diene derivative for preparation of miyakosyne A and stereoisomers [440], with allylic alcohols for six-membered ring carbohydrate syntheses [441], and with an allylpiperidine derivative (e.g. 135) for total synthesis of himeradine A [442]; (2) methacrolein with an alkene spiroacetal for total synthesis of bistramide A [443]; (3) methyl vinyl ketone with allylic alcohols as part of a general arylamine synthesis route [444]; (4) various enones, acrylates, and allylic alcohols with 4-pentylpyranones [445]; (5) various acrylate esters with undeca-1,9-dien-6-ol derivatives (e.g.…”