Rhodium(I)-Catalyzed O-H Insertions on O-Protected α-Diazo-β-Hydroxyesters

The X-H insertion reaction constitutes a powerful tool to create diversity through the diazo decomposition of diazocarbonyl compounds. However, until now, X-H insertion on α-diazo-β-aryl-β-hydroxyester scaffolds, readily prepared by aldol-type addition, remained a challenge for the organic chemist. We report herein the first O-H insertions on O-protected α-diazo-β-aryl-β-hydroxyesters, providing straightforward access to a wide range of α,β-dioxygenated esters through modulation of the alcohol and of the aryl substituent. The key feature to achieving this transformation is the use of Rh(I) catalysts, which proved to be crucial to favor the targeted O-H insertion product over the competing 1,2-H and 1,2-Ar migration products. Overall, 32 O-H insertion products have been prepared, in moderate to good yields, with a diastereoisomeric ratio up to 7.5:1 in favor of the syn diastereoisomer.

Acid-Catalyzed Decomposition of O-Silylated α-Diazo-β-hydroxy Esters: Access to Mixed Monosilyl Acetals

Acid-catalyzed decomposition of diazocarbonyl compounds triggers a wide range of transformations leading to synthetically useful building blocks with high diversity. In this field, the chemistry of α-diazo-β-hydroxy ester substrates is largely dominated by migration processes. We describe herein a new approach to original mixed monosilyl acetals from O-protected α-diazo-β-hydroxy-β-aryl esters and alcohols, catalyzed by trimethylsilyl trifluoromethanesulfonate (TMSOTf). The ratio between these original mixed acetals, the symmetric acetals, and the migration products fluctuates depending on the catalyst, the nature of the alcohols, and the substituent on the aromatic ring. Fifty-six examples are reported herein with yields up to 71% and diastereoselectivity up to 6:1. Such mixed monosilyl acetals constitute a synthetic equivalent of α-substituted β-oxoesters with high potential for further transformations.