Abstract With (E/Z)-isomeric phytyl halides as side-chain materials, vitamin K 1 is synthesized via a Diels–Alder reaction to activate the free bridgehead hydrogen of 3 for the alkylation and a retro-Diels–Alder reaction to eliminate cyclopentadiene from 2 in a high
[Redondo, Maria C.; Veguillas, Marcos; Ribagorda, Maria; Carreno, M. Carmen Angewandte Chemie - International Edition, 2009 , vol. 48, # 2 p. 370 - 374]