Chemoselective Transesterification of β-Keto Esters under Neutral Conditions using NBS as a Catalyst

Abstract

Facile and selective transesterification of b-keto esters using N-bromosuccinimide (NBS) as an efficient and neutral catalyst is described.

Studies of the Electronic Effects of Zinc Cluster Catalysts and Their Application to the Transesterification of β‐Keto Esters

“…[1] In addition, unlike simple esters, the chelation nature of b-keto esters suppresses the activity of metal catalysts through the formation of ac oordinate bond to metal ions, and the acidic nature of b-keto esters (pK a % 14 in DMSO) suppresses the activity of the base catalyst. To date, several acidic and basic catalysts, such as DMAP, [17,28] zeolites, [29] super acid, [30] montmorillonite, [31] Zn/I 2 , [15a] amberlyst-15, [32] Nb 2 O 5 , [33] N-bromosuccinimide (NBS), [34] Al(H 2 PO 4 ) 3 , [35] and BiCl 3 , [36] have been used for the transesterification of b-keto esters. The substrate generality of b-keto esters, however,h as much room for improvement.A lmost all of the substrates used for the reactions were a-unsubstituted simple b-keto esters, and reactions of sterically more congested a-substituted b-keto esters have not been well studied.…”

The Acylation of Heteroatoms

“…Esters of b-keto acids can also be conveniently prepared from other keto esters by transesterification [27,28]. An alternative to direct acylation with b-keto acids is thermolysis of acyl Meldrum's acid (to generate an acylketene) in the presence of a nucleophile (Scheme 7.7).…”

“…Under neutral or acidic reaction conditions acylation of the hydroxyl group predominates [27,[64][65][66] whereas basic reaction conditions favor acylation of the mercapto group (Scheme 7.18). Mercaptoalcohols can also be acylated with high regioselectivity.…”

Kinetics of Oxidation of Amino Acids by a Newly Synthesized Oxidant, N-Chloropyrazinamide in Aqueous Acetic Acid Medium

“…A mixture of NCPZA (0.04 M), glycine (0.02 M), hydrochloric acid (0.5 M) and NaClO 4 . H 2 O (0.10 M) was made upto 25 ml in 50 % acetic acid -50 % water mixture.…”