Synthesis: Whitlock, J. Am. Chem. Soc. 84, 3412 (1962); Gautier, Deslongchamps, Can. J. Chem. 45, 297 (1967); Whitlock, Siefken, J. Am. Chem. Soc. 90, 4929 (1968). Absolute configuration: Keiichi et al., Tetrahedron Lett. 1968, 5467.