Next, the enolate complex adds to the pyrone through a Diels-Alder concerted reaction to form a bicyclic intermediate ( "'8 "').
12.
2-Pyrone is used in organic synthesis as a building block for more complex chemical structures because it may participate in a variety of cycloaddition reactions to form bicyclic lactones.
13.
Then, the coordinated enolate can either add to the 2-pyrone ( "'3 "') through a Michael-aldol or Diels-Alder pathway.
14.
The furan monoadduct can absorb a second UVA photon leading to a second four-center photocycloaddition at the pyrone end of the molecule and hence the formation of a diadduct or cross-link.
15.
Tipranavir is a nonpeptidic HIV-1 protease inhibitor This sulfonamide containing 5, 6-dihydro-4-hydroxy-2-pyrone had emerged from screenings of 3-substituted coumarins and dihydropyrones.
16.
The photochemically reactive sites in psoralens are located at each of the carbon-carbon double bonds in the furan ring ( the five-member ring ) and the pyrone ring ( the six-member ring ).
17.
In the Michael-aldol pathway ( "'Scheme 2 "'), The coordinated oxaloacetate enolate performs a Michael addition to the ring of the pyrone to form intermediate "'4 " '.
18.
Chemically, quercetin is a member of a fairly extensive class of natural coloring matters derived from phenyl benzoyl-pyrone or flavone, the constitution of which followed on the researches of St von Kostanecki, A . G . Perkin, Herzig, Goldschmidt and others.
19.
The unusual multistep conversion of 5-acetyl-4-methoxy-6-methyl-2-pyrone ( "'3 "') to macrophomic acid is thought to proceed by either a concerted Diels-Alder reaction or a recently proposed 2-step Michael-aldol sequence.
20.
The intermolecular reaction of the hydroxy-pyrone and ?, ? unsaturated ester shown below suffered from poor yield and regioselectivity; however, when directed by phenylboronic acid the desired adduct could be obtained in 61 % yield after cleavage of the boronate with 2, 2-dimethyl-1, 3-propanediol.
