A survey of the molecular rotation data and an examination of the characteristics of the UV absorption spectrum of desoxosipeimone (desoxodihydroimperialon, Ⅱ), coupled with biogenetic considerations, appear to favour the location of the secondary hydroxyl group in sipeimine (imperialin) at C-3.The carbonyl group of sipeimine is tentatively assigned to C-6 in order to account for the unusual chemical and spectral properties of anhydrosipeimine (Ⅹ), which seems to be-have like a cyclopropyl ketone.In the meantime, an extensive study of existing rotation data indicates that position-6 is equally acceptable as position-7 as the site of the carbonyl.The latter position has been favoured by Morgan and Barltrop^[11].The location of the tertiary hydroxyl group and the stereochemistry of the rings A and B are discussed.The structure of sipeimine (imperialin) is provisionally presented as (XIV).