117470-84-5Relevant academic research and scientific papers
Mono- vs. dialkylation of carbanions. Effects of absolute and relative acidity of the conjugate carbon acids in selectivity control
Ridvan, Ludek,Zavada, Jiri
, p. 14793 - 14806 (2007/10/03)
The title problem was investigated in the reaction of the dibromide 1 with carbanions 2a-2g covering a range greater than 15 pK units in DMSO. It was found that the bis(monoalkylated) product 3 arises exclusively or predominantly from the carbanions 2d-2g derived from the less acidic carbon acids 7d-7g whereas the cyclic product of dialkylation 4 prevails in the reaction of the carbanions 2a-2c derived from the more acidic carbon acids 7a-7c. The alkylation selectivity thus depends critically on the absolute acidity of the carbon acid participating in the reaction. Rationale for this novel, and on basis of earlier studies unexpected finding is provided in terms of eqs. (1)-(4).
Acidities of Glycine Schiff Bases and Alkylation of Their Conjugate Bases
O'Donnell, Martin J.,Bennett, William D.,Bruder, Willian A.,Jacobsen, William N.,Knuth, Keith,et al.
, p. 8520 - 8525 (2007/10/02)
Equilibrium acidities in Me2SO are reported for six ketimines of the type Ph2C=NCH(R)CO2Et and five aldimines, ArCH=NCH(R)CO2Et.Changing R in the ketimine from H to Ph increased the pKa by 2.2 units.This surprising acidity decrease for Ph substitution points to a substantial increase in steric effect, as do the increases in pKa of 3.8 and 4.2 units observed for the replacement of hydrogen by Me and PhCH2, respectively.Phase-transfer alkylation of the Ph2C=NCH2CO2Et ketimine gave over 90 percent of monoalkylate whereas, under similar conditions, the aldimine 4-ClC6H4CH=NCH2CO2Et gave a mixture of mono- and dialkylate.The difference is that the pKa of the monoalkylated aldimine is essentially the same as that of the parent, which leads to rapid equilibration with the parent anion and consequent dialkylation.The rates of alkylation in Me2SO of these parent and monoalkylated anions did not differ greatly, showing that the relative pKHAs of the parent acid and its monoalkyl derivative, rather tham the relative rates of the mono- and dialkylation reactions, is the principal factor that determines the extent of the competition between monoalkylation and dialkylation.
