The Gods Hath Decreed that there be no citations pertaining directly to this step. However, here are some cool citations from other steps.

Original citation: Afarinkia, K.; Vinader, V.; Nelson, T. D.; Posner, G. H. Tetrahedron 1992, 48, 9111-9171
This article referenced the ability of pyrones and pyridones to perform Diels-Alder reactions at high temperatures as either a diene or a dienophile. With this
process, one can produce stereoselective bicyclic systems and with an alkyne and loss of carbon dioxide, change a pyrone into a benzene ring while
mainatining stereochemistry and R-groups.

Articles that cited this article:
Hoshino, M.; Matsuzaki, H.; Fujita, R. Chem. Pharm. Bull 2008, 56, 480-484.
This article referenced K. Afrarinka's discussion on the use of pyridones as dienes in Diels-Alder reactions, especially this reaction, which was expanded upon
by M. Hoshino et al by adding R substituents to the pyridone.
Kozytska, M. V.; Dudley, G. B. Tetrahedron Lett. 2008, 49, 2899-2901.
The article uses principles first noted in K. Afarinka's article about the use of a pyrones as a diene in Diels-Alder reactions. The retrosynthetic analysis used in
the cited article relied on an intermolecular Diels-Alder reaction with this molecule (not drawn 3-D) with the pyrone substituent acting as the diene.
Carbaugh, A. D.; Vosburg, W.; Scherer, T. J.; Castillo, C. E.; Christianson, M. A.; Kostarellas, J.; Gosai, S. J.; Leonard, M. S. ARKIVOC. 2007, xii, 43-
54.
While using the same principles as K. Afarinka in the formation of bicyclic rings using pyrones, Carbaugh, et al noted that one can remove CO2 from the
bicyclic ring following a Diels-Alder reaction with a pyrone to get a benzene derivative.