## 3 Results
### Homologation of Intermediate 1 with ICH\({}_{2}\)ZnCH\({}_{2}\)I
#### 3.4.1 Attack through the Direction Opposite the Oxazolidinone Carbonyl
Finally, the remnants of the Cu-CH\({}_{2}\) bond are replaced by the formation of a half-bond between Cu and the non-heterosubstituted carbon of the C=C bond, simultaneously with the further loss of some of its double-bond character. This complex electronic rearrangement occurs spontaneously without additional transition states, and yields a very stable intermediate (Int2) that lies 34.2 kcal-mol\({}^{-1}\) below the pre-reactional complex. The alternative formation of an intermediate bearing the new CH\({}_{2}\) group on the opposite carbon (Int2\({}^{\prime}\)) is thermodynamically much less favored, since Int2\({}^{\prime}\) lies 22.3 kcal-mol\({}^{-1}\) above Int2. Separate analysis of the energies of the individual fragments (Table 2) shows that the relative instability of Int2\({}^{\prime}\) is not due to geometric constrains that affect the stabilization of the Zn-containing  
Figure 6: Important structures in the pathway towards intermediate 2 (Int2). (**A**) Int1:(CuI:THF):(MgBr:THF); (**B**) Int1:CuI + ICH\({}_{2}\)ZnCH\({}_{2}\)I pre-reactional complex; (**C**) TS2; (**D**) Int2; (**E**) Int2\({}^{\prime}\); (**F**) Potential energy surface of the zinc homolog of Mg-free Int1. The blue line refers to the attack from the “un-encumbered” direction (leading to isomer “\(\alpha\)” of Int2), whereas the red line describes homologation from the “encumbered” reaction, leading to isomer “\(\beta\)” of Int2. moiety by the oxazolidinone, but to the intrinsically higher energy of the organic moiety of Int2\({}^{\prime}\) (compared to that of Int2). Two products of the attack on Int1 are possible (Int2\(\alpha\) and Int2\(\beta\)) depending on the direction of approach of the Simmons-Smith-Furukawa zinc carbenoid relative to the plane formed by the C=C bond and the coordinating CuI. Those attacks are not equally favored because in one of them (which we will designate as \"attack from below the plane of the oxazolidine ring\", or \"encumbered\") the attacking zinc carbenoid may clash with the substituent on the oxazolidinone ring (methyl), in our models, or the bulkier phenylmethyl in the experimental setup). Our computations reveal that, indeed, when the attack proceeds from below the ring plane, the steric interaction of the ring substituent with the zinc carbenoid increases the transition state energy by a modest amount (1.6 kcal\(\cdot\)mol\({}^{-1}\)). Although the reaction is thermodynamically more favorable (by 1.8 kcal\(\cdot\)mol\({}^{-1}\)) than in the attack from the direction above the ring, the high spontaneity of the reaction (exergonic by more than 34 kcal\(\cdot\)mol\({}^{-1}\) in both cases) entails that the reverse reactions will have too large an activation energy and the reaction outcome will therefore be kinetically-controlled (rather than thermodynamically-controlled), leading to a non-racemic mixture of the two products where the one arising from the attack of Int1 by the zinc compound from the \"un-encumbered\" direction (Int2\(\alpha\)) will be predominant (Figure 6F). \begin{table}
\begin{tabular}{c c c c} \hline \hline  & **Int2** & **Int2\({}^{\prime}\)** & **Int2–Int2\({}^{\prime}\)** \\ \hline organic moiety & \(-\)348,955.2 & \(-\)348,892.7 & \(-\)62.5 \\ organic moiety + CuI & \(-\)478,913.8 & \(-\)478,885.5 & \(-\)28.3 \\ ZnI(CH2I) & \(-\)180,031.3 & \(-\)180,030.3 & \(-\)1.1 \\ Full molecule & \(-\)659,304.2 & \(-\)659,283.0 & \(-\)21.3 \\ interaction between ZnI(CH2I) and organic-CuI & \(-\)359.2 & \(-\)367.2 & 8.1 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Electronic energies including solvation effects in THF (in kcal\(\cdot\)mol\({}^{-1}\)) of individual fragments of intermediates 2 and 2\({}^{\prime}\), computed with the PBEPW91 density-functional. Computations of the energies of the individual fragments have been performed at the same geometry as that in the full molecule. The electron pair in the severed bond between the organic moiety and ZnI(CH2I) was divided symmetrically between the fragments.