The structure and stereochemistry of the tricyclic sesquiterpene alcohol (-)-presilphiperfolanol, a structural precursor for the angular and propellane triquinane sesquiterpenes, are established as (1S,4S,7S,8S,11S)-2,2,4,8-tetramethyltricyclo[5.3.1.0(4,11)] undecan-11-ol [[2aS-(2a alpha,4a beta,5 beta,7a beta,7b beta)]-decahydro-1,1,2a,5-tetramethyl-7bH-cyclopenta[cd]inden-7b-ol, 1] by an X-ray crystallographic analysis of its p-nitrobenzoate derivative 8a and by correlation with (-)-silphiperfol-6-ene (6). Dehydration of 1 afforded a 2:1 mixture of presilphiperfol-1(8)- and 7-enes (9 + 10) which underwent epoxidation on both alpha and beta faces, Acid-catalyzed dehydration with H2SO4-silica gel lead to competing ring contractions by migrations oi. C11 and C9 to C8 la give silphiperfolene (6) and alpha-terrecyclene (12) in a 98:1 ratio. Solvolysis of 8a in 60% aqueous acetone provided a mixture of olefins (9 + 10 + 6) and 1 (9%) as the sole alcohol product. The similarity of the solvolysis rate (5.2 x 10(-5) s(-1) at 50 degrees C) to the literature value for trans-bicyclo[3,3,0]octan-1-yl p-nitrobenzoate indicates comparable levels of strain relief in the respective transition states.