Enantioselectivity substitution

As discussed in CbapL 6, copper-mediated diasteteoselective addition and substitution reactions ate well studied metliods for the construction of chiral centers in organic molecules. Tlie development of coppet-mediated enantioselective substitution reactions, however, is still at an early stage. 

Metalated SAMP- or RAMP-hydrazones derived from alkyl- or arylethyl ketones 3 add to arylaldehydes both diastereo- and enantioselectively. Substituted / -hydroxy ketones with relative syn configuration of the major diastereomer are obtained with de 51-80% and 70-80% ee. However, recrystallization of the aldol adducts, followed by ozonolysis, furnishes diastereo- and enantiomerically pure (lS, S )-. yn-a-mcthyl-/3-hydroxy ketones 5 in 36-51% overall yield. The absolute configuration of the aldol adducts was established by X-ray crystallographic analysis. Starting from the SAMP- or RAMP-hydrazone either enantiomer, (S,S) or (R,R), is available using this methodology16. 

Scheme 8.8. Enantioselective substitution of oxazolin-2-yl and thiazolin-2-yl allyl thioethers.

Complex 2b also catalyzes the addition of imidazoles, benzimidazoles, and several purines to methyl allylic carbonates (Scheme 26) [76]. These reactions occurred with good yields and excellent enantioselectivities. -substituted heterocycles are found in a number of compounds that exhibit a range of biological activity. The syntheses of several pharmacologically active compounds were conducted with yields that were improved over those published previously. 

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