Diels-Alder Cycloaddition: Nicolaioidesin B (Coster), Lycorine (Cho), Bucidarasin A (Nakada), Maoecrystal V (Thomson), Kuwanon J (Wulff/Lei), Vinigrol (Kaliappan)
β-Ocimene (2) is an inexpensive Diels-Alder diene. En route to Nicolaioidesin B (4), Mark J. Coster of Griffith University showed (Tetrahedron Lett. 2014, 55, 6864. ) that the Weinreb amide 1 added to the E isomer of 2 with high selectivity, to give 3.
The alkaloid Lycorine (8) is found throughout the Amaryllidacae. Cheon-Gyu Cho of Hanyang University developed (Org. Lett. 2014, 16, 5718. ) a succinct route to 8 based on the use of the boryl styrene 5 as a Diels-Alder dienophile.
Masahisa Nakada of Waseda University (Org. Lett. 2014, 16, 4734. ) prepared the enantiomerically-pure enone 9 by way of a baker’s yeast reduction of a prochiral diketone. Diels-Alder addition to 10 led to 11, that was carried on to Bucidirasin A (12).
Regan J. Thomson of Northwestern University prepared (J. Am. Chem. Soc. 2014, 136, 17750. ) the triene 13 by asymmetric epoxidation of a prochiral enone. Diels-Alder addition of the very reactive nitroethylene to give 14 completed the carbon skeleton of Maoecrystal V (15).
William D. Wulff of Michigan State University and Xiaoguang Lei of Peking University optimized (Angew. Chem. Int. Ed. 2014, 53, 9257. )the organocatalyzed Diels-Alder cycloaddition of 17 to the diene 16. Deprotection then completed the synthesis of the prenylflavonoid Kuwanon J (18).
In 2012, Barriault described ( 2012, December 24) the conversion of 20 to the complex diterpene Vinigrol (21). Krishna P. Paliappan of the Indian Institute of Technology Bombay showed (Org. Lett. 2014, 16, 5540. ) that the triene precursor to 20 could be prepared by ring-closing metathesis of 19. In the absence of ethylene, a different product was formed.