... The precise mechanism for the elimination of the C-5 hydroxy group was recently elucidated by the Sun and Leadlay groups and shown to proceed via acetylation and subsequent elimination, thereby forming dienophile 19.(20) An intramolecular Diels–Alder (IMDA) reaction ...
[Nakahata, Masaaki; Imaida, Motomasa; Ozaki, Hiroshi; Harada, Tadao; Tai, Akira Bulletin of the Chemical Society of Japan, 1982 , vol. 55, # 7 p. 2186 - 2189]