QUADRANT RULE FOR THE PREDICTION OF CHIROPTICAL EFFECTS OF OPTICALLY-ACTIVE HOMOANNULAR CISOID DIENES

An empirical analysis for the chiroptical effects of cisoid homoannular dienes called the diene quadrant rule is presented. This regional rule uses a cubic space divided into quadrants in order to assign relative signs of the rotatory contribution of the diene and axial allylic substituents. The magnitude of the contribution of axial allylic substituents is estimated from their stereochemical relationship to the adjacent double bonds. Assumptions are made about the relative contributions of axial allylic hydrogen vs. methyl. The total Δε is considered to consist of Δε = δdiene-[δx sin2 w + δx’ sin2 w], where δdiene is the contribution of the diene, and δx and δx’ are substituent contributions at torsional angle of co to the adjacent olefinic unit. The algebraic sum derives from the orientation of the diene and axial allylic moieties inscribed within the cubic space. The diene quadrant rule is applied successfully to known exceptions to the original diene chirality rule. © 1979, American Chemical Society. All rights reserved.