Recent advances in N-heterocyclic carbene (NHC)-catalysed benzoin reactions

• Rajeev S. Menon,
• Akkattu T. Biju and
• Vijay Nair

Beilstein J. Org. Chem. 2016, 12, 444–461, doi:10.3762/bjoc.12.47

• -2-amino3-hydroxyindanones is catalysed by NHC 31. The imine electrophile is generated in situ from α-sulfonyl-N-Boc amine 33 (Scheme 19). Initial cross-aza-benzoin reaction of one of the aldehyde functionalities with the imine is followed by an intramolecular aldol reaction to furnish the indanone

• framework [35]. The thiazolium precatalyst 31 can also efficiently mediate cross-aza-benzoin reactions of aromatic and heteroaromatic aldehydes with unactivated aromatic imines 34 (Scheme 20) [36]. A control reaction of the corresponding benzoin (instead of the aldehyde) and imine 34 also afforded the α

• -amino ketone product 35 in 71% yield. This indicates that the reaction involves reversible formation of aldehyde-homobenzoin adducts. Enantioselective cross aza-benzoin reaction of aliphatic aldehydes with N-Boc-protected imines are promoted efficiently by NHC generated from the chiral triazolium salt

N-Heterocyclic carbene-catalyzed direct cross-aza-benzoin reaction: Efficient synthesis of α-amino-β-keto esters

• Takuya Uno,
• Yusuke Kobayashi and
• Yoshiji Takemoto

Beilstein J. Org. Chem. 2012, 8, 1499–1504, doi:10.3762/bjoc.8.169

• -amino-β-keto esters; cross-aza-benzoin; α-imino ester; N-heterocyclic carbenes; organocatalysis; umpolung reactions; Introduction α-Amino-β-keto ester derivatives are one of the fundamental structural subunits in natural products such as miuraenamides [1], and important building blocks for the

• ][28][29][30][31][32][33][34], the related reactions of aldehydes with imines, i.e., the cross-aza-benzoin reactions, have been much less studied, in spite of the pharmaceutical and biological importance of providing α-amino ketones [35][36][37][38][39][40][41][42][43]. In particular, a reaction

• protecting groups of the nitrogen atom of α-imino esters 2, which have been known to be excellent electrophiles, would suppress an unexpected reaction of 2 with NHCs, enabling the direct use of 2 as acyl anion acceptors in the cross-aza-benzoin reaction. In this communication, we describe a new, efficient