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11the particular alkene substrate. 17 The alkene will have a “large” substituentconnected to it and a “small” substituent connected to it (Figure 7). Jacobsen’scatalyst has two chiral centers on the cyclohexane ring whose configurations areeither (R,R) or (S,S). Depending upon the configuration, the axial hydrogenconnected to those two chiral centers will be on either the left side of the catalyst(R,R) or on the right side of the catalyst (S,S). When the alkene adds across thetop of the Manganese-oxo species, it will attack in a way that the “large”substituent on the alkene will situate itself in a position remote to the axialhydrogen. This selective approach is the source of the stereoselectivity of theepoxidation.By applying this mechanism to citronellyl pivalate, it can be shown that the“large” substituent would approach the manganese-oxo complex in a way remoteto the axial hydrogen on Jacobsen’s catalyst and the “small” substituent would bebetter accommodated closer to the axial hydrogen (Figure 8). This mechanism canalso be used to predict the stereochemistry of the newly synthesized epoxide. 17 Byusing the (S,S) Jacobsen’s catalyst, we can make the needed (3S,6S)-6,7-epoxycitronellyl pivalate.3-D images generated by the molecular modeling program PC Spartanfurther validate this proposed mechanism. Figure 9 shows a 3-D view ofJacobsen’s catalyst from the top. From this view, it can readily be seen that thebulky t-butyl groups prevent approach to the centrally located manganese-oxogroup. It can also be seen that the axial hydrogen controls approach from acrossthe cyclohexane ring on top. Figure 10 shows Jacobsen’s catalyst from a flatperspective. This figure displays the prominent oxygen atom at the top of the