Frederick G. Bordwell

Substrate acidities and conversion times for reactions of amides with di-tert-butyl bicarbonate

Abstract The conversion time tor 4-dimethylaminopyndine catalysed reaction of amides with di- tert -butyl dicarbonate varies dramatically with substrate acidity. The pK a s in DMSO of some amides are determined to support correlation of reactivity with substrate acidity. Particularly acidic substrates, such as 4-thiazolidinone, readily react with a variety of dialkyl dicarbonates. Less acidic substrates react with Boc 2 O but other dialkyl dicarbonates decompose preferentially.

EFFECTS OF SULFENYL, SULFINYL AND SULFONYL GROUPS ON ACIDITIES AND HOMOLYTIC BOND DISSOCIATION ENERGIES OF ADJACENT C-H AND N-H BONDS

Acidities and bond dissociation energies (BDEs) of the N–H bond in two phenylsulfenylamides, PhSNHBz and PhSNH-t-Bu, and four phenylsulfenylanilides, 4-GC6H4NHSPh, where G  =  MeO, H, Br and CN, were measured in order to compare the effects of substituents on acidities and BDEs of N—H bonds with those of C—H bonds. The effects of PhS groups on acidities and BDEs in a series of C—H acids were found to be comparable to those on acidities and BDEs of PhS in a similar series of N—H acids. Comparisons were also made of the effects of changing the oxidation state of sulfur in the series PhS, PhSO and PhSO2 on the acidities and BDEs of adjacent N—H and C—H bonds in weak acids. Hammett-type plots of pKHA values for phenyl benzyl sulfones (4-GC6H4CH2SO2Ph) and phenylsulfenylanilides (4-GC6H4NHSPh) were linear vs σp− values. A linear plot was obtained and explained for a plot of BDE of the N—H bonds in remotely substituted phenylsulfonylanilides with σ+ values. Plots of BDEs vs Eox(A−) were also linear for 4-substituted phenylsulfenylanilides (4-GC6H4NHSPh), phenylsulfonylanilides (4-GC6H4NHSO2Ph) and phenyl benzyl sulfones (4-GC6H4CH2SO2Ph).

Triisopropylsilanol: A new type of phase transfer catalyst for dehydrohalogenation

Abstract A new solid-liquid phase transfer catalyst, trisopropylsilanol (TIPSOH), has been developed which, through the silanol/silanoate system, allows KOH to quantitatively convert even primary alkyl halides to alkenes avoiding both ether and alcohol by-products. Its potential application in the detoxification of mustard gas analogues and environmental pollutants has been demonstrated.

Preparation of an α-aminophosphonate cation equivalent and its reaction with organoboranes

Abstract Compound 5 , an α-aminophosphonate cation equivalent ( 2 ), is reacted with organoboranes to yield α-substituted α-aminophosphonic acid derivatives 7 .

Equilibrium acidities and homolytic bond dissociation enthalpies of m- and p-substituted benzaldoximes and phenyl methyl ketoximes

The equilibrium acidities in DMSO of nine p- and m-substituted benzaldoximes and eight p-substituted phenyl methyl ketoximes were measured. Estimates of the homolytic bond dissociation energies (BDEs) of the acidic O—H bonds in these compounds were made by combination of their pKHA values with the oxidation potentials of their conjugate bases, Eox(A−), using the equation BDE  =  1.37pKHA + 23.06Eox(A−) + 73.3 kcal (1 kcal  =  4.184 KJ). Plots of Eox(A−) vs pKHA for p-substituted benzaldoximes and p-substituted phenyl methyl ketoximes were linear with slopes near unity. Consequently, as required by the above equation, the BDEs estimated for the O—H bonds in these oximes were constant, being 88.3 ± 0.3 and 89.2 ± 0.4 kcal, respectively.

Equilibrium acidities of HA2+ dications in dimethyl sulfoxide solution

A potentially general method for estimating the acidities of HA 2+ dications in DMSO solution based on a thermodynamic cycle has been developed by combination of the equilibrium acidity of the acid (PK HA ) with its oxidation potential [E ox (HA)], the oxidation potential of its conjugate base [E ox (A - )], and those of the corresponding radical [E ox (A . )] and radical cation [E ox (HA +. )] (eq 6). The pK HA+. values for the radical cations derived from 2,4,5-triphenylimidazole, p-(phenylamino)diphenylamine, and 5H-dibenz[bf]azepine (iminostilbene) by loss of an electron were found to be 1.5, 4.1, and 3.8, respectively, and the pK HA2+ values of the corresponding dications formed by loss of an electron from these radical cations were found to be -8. 1, -5.7, and -7.7, respectively