Thermal sigmatropic rearrangements of vinylallenes leading to 11-cis-retinoids and the novel properties of 9-cis,11-cis,13-cis-retinal and 11-cis,13-cis-retinal
[1,5]-Sigmatropic rearrangement of vinylallenes: a novel route to geometric isomers of the retinoids possessing 11-cis linkages including 9,11,13-tricis-retinal