Group inversion

The role of the ligands is both to stabilize the Pd(0) state and to tune the reactivity of the palladium. The outline mechanism above does not specify many detailed aspects of the reaction that are important to understanding the effect of ligands, added salts, and solvents. Moreover, it does not address the stereochemistry, either in terms of the Pd center (tetracoordinate pentacoordinate , cisl, transl) or of the reacting carbon groups (inversion , retention ). Some of these issues are addressed by a more detailed mechanism.190... 

Every member of the group has a reciprocal such that B B 1 = B 1 B = E where the reciprocal is also a member of the group (inverse). 

Recent studies on the solvolysis of the diastereomeric tosylates 107 support this hypothesis. The acetolysis and formolysis of these compounds proceed with high retention of configuration 90> while in ordinary simple acetolysis of tosyl esters of secondary alcohols containing no neighboring groups, inversion predominates. 

Chiral substituted 1,2,3-dithiazolidine (48) converts slowly at RT into its stereoisomer (49) by S=0 group inversion which relieves the steric interaction with both methyl and phenyl groups (Equation (2)). The freshly prepared mixture (48) (49) = 4.4 1 (Section 4.11.8.3), when kept at 0°C in the presence of Et4N+Cl , exhibits a change of the equilibrium to 9 1 in 24 h and to 34 1 in the next 24 h, further progress being hampered by slow decomposition of (49) <91TL5885>. 

A. Dondoni, G. Fantin, M. Fogagnolo, A. Medici, and P. Pedrini, Hydroxy group inversion in thiazole polyols by an oxidation-reduction sequence. An entry to syn 1,2-diol fragments in masked carbohydrates, J. Org. Chem. 54 702 (1989). 

SN2 Backside attack of C bonded to L (the leaving group), inversion of stereochemical configuration second order kinetics (Nu attack sets rate). 

Although the methyl group inversion appears to be analogue to that of ammonia, there exits a fluorine atom, which has to pass through the carbon atom, which is indeed energertically prohibited. 

Cleavage between oxygen and alkyl group inversion... 

In these reactions, retention can only be accommodated by formation of a phosphorane intermediate, followed by pseudorotation, before loss of the leaving group. Inversion could result either from a concerted reaction, or a stepwise process, if the phosphorane collapses before pseudorotation can occur. The stereochemical and LFER data indicate that both mechanisms occur. In a study of similar cyclic triesters (Fig. 12c and d) that combined LFER studies, stereochemical analysis, and solvent isotope effects, Rowell and Gorenstein found a trend in / g values as a function of attacking nucleophile.61 These, and the stereochemical data, are strong evidence for a mechanistic continuum from concerted to stepwise reactions of six-membered cyclic phosphate triesters.61... 

The main operation in the computation of a group inverse is the computation... 

Thioaldehydes 1 exhibit high endo selectivity in the hetero-Diels-Alder reaction with cyclopen-tadiene (2), but only moderate facial selectivity. In the case of aldehyde Id, bearing a free hydroxy group, inversion of the asymmetric induction is observed63. 

Derivatization of 26 shows only a low selectivity between the 4- and 5-position. The presence of a dithiane group in each bridge however reveals a clear preference for 5-substitution. Functional group inversion of dithiane groups led to the preparation of numerous other metacyclophanes [116, 117]. Unsymme-trically substituted metacyclophanes are chiral and the corresponding enantiomers were separated [152]. Recently the enantiomeric pure cyclophane 171 was... 

Most of the measured lines are split into two (0 and 0 ) components due to the amino group inversion. 

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