Main observation and conclusionrnThe asymmetric total synthesis of an unusual C25 steroid containing a unique bicyclo[4.4.1]undecene A/B ring system,resulting in the synthesis of cyclocitrinol (1) and its isomer Δ8,14-cyclocitrinol (38),is reported.Initial attempts to construct the synthetically challenging bicyclo[4.4.1]undecene A/B ring system using a type Ⅱ [5+2] cycloaddition showed that a chiral substituent at the allylic position of the alkene (C6,cyclocitrinol numbering) controlled the stereoselective outcome of the cycloaddition reaction.Late-stage migration of the tetrasubstituted C8-C14 double bond in A8,14-cydocitrinol (38) to obtain cyclocitrinol (1) proved challenging,inspiring an alternative approach.The chiral β-CH2OR group on the allylic substituent at C6 played a pivotal role both in controlling the diastereoselectivity of the type Ⅱ [5+2] cycloaddition and retaining the C6 substituent under lithium-amine conditions.