O. Jacobsen, Ber, 19,1209(1886);20,901(1887)
L.I. Smith in Organic Reactions I, 370(1942)
L.I. Smith, C.P. Lo, J. Am.Chem. Soc. 70, 2209,(1948) and earlier papers
E.N. Marvell, P.G. Olafson, D. Lini, R. Barbour, R. Dueltgen, J. Org. Chem., 28 3248(1963)