Paper
Organic & Biomolecular Chemistry
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asymmetric
homobenzoin
condensation
see:
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21 Very recently Milo et al. have shown that product ee can be 32 This is despite convincing evidence (see ref. 31) that ben-
improved through the simple step of adding a small excess
(relative to the catalyst) of aryl boronic acids, see:
V. Dhayalan, S. C. Gadekar, Z. Alassad and A. Milo, Nat.
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zaldehydes equipped with an o-heteroatom are attacked by
NHCs faster than benzaldehyde itself. It is clear that in
such (reversible) crossed benzoin condensations chemo-
selectivity is not determined by the relative rates of the first
attack of the carbene on the two aldehydes. For a more in
depth discussion see ref. 27.
22 For an approach involving a chiral metallophosphite cata-
lyst (and acylsilanes as one coupling partner instead of
Org. Biomol. Chem.
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