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The polycyclization of (3S)-2,3-oxidosqualene to the tetracyclic protosteryl cation was studied to determine if the full course of the cyclizations is governed by a specific localized torsion at bond 11-12 in the acyclic precursor polyene. Experiments were performed wherein aldehyde in CH2Cl2 is treated with SnCl4 at room temperature. The concentrations of the cyclization products were then obtained by GC measurements. Results showed that the cyclization led to the formation of a trans-fused angular methyl-substituted CD-ring system involving a true anti-Markovnikov closure.