Dina C. Merrer

Conversion of ‘obstinate’ nitriles to amidines by Garigipati's reaction

Summary Reaction with methylchloroaluminum amide readily converts sterically hindered nitriles to amidines.

STRUCTURE-REACTIVITY DEPENDENCE IN THE REARRANGEMENTS OF A FAMILY OF ALKYLACETOXYCARBENES

Abstract Absolute rate constants and activation parameters are presented for the 1,2-H and 1,2-acetyl migrations of a family of alkylacetoxycarbenes.

Benzylfluorocarbene: Reactions and kinetics

Abstract Benzylfluorocarbene, generated from the corresponding diazirine, is accompanied by considerable azine formation. Its rearrangement to β-fluorostyrene isomers in tetrachloroethane is characterized by E a = 3.2 kcal/mol and log A = 9.5 s −1

Experimental and Computational Mechanistic Investigation of Chlorocarbene Additions to Bridgehead Carbene–Anti-Bredt Systems: Noradamantylcarbene–Adamantene and Adamantylcarbene–Homoadamantene

Cophotolysis of noradamantyldiazirine with the phenanthride precursor of dichlorocarbene or phenylchlorodiazirine in pentane at room temperature produces noradamantylethylenes in 11% yield with slight diastereoselectivity. Cophotolysis of adamantyldiazirine with phenylchlorodiazirine in pentane at room temperature generates adamantylethylenes in 6% yield with no diastereoselectivity. (1)H NMR showed the reaction of noradamantyldiazirine + phenylchlorodiazirine to be independent of solvent, and the rate of noradamantyldiazirine consumption correlated with the rate of ethylene formation. Laser flash photolysis showed that reaction of phenylchlorocarbene + adamantene was independent of adamantene concentration. The reaction of phenylchlorocarbene + homoadamantene produces the ethylene products with k = 9.6 × 10(5) M(-1) s(-1). Calculations at the UB3LYP/6-31+G(d,p) and UM062X/6-31+G(d,p)//UB3LYP/6-31+G(d,p) levels show the formation of exocyclic ethylenes to proceed (a) on the singlet surface via stepwise addition of phenylchlorocarbene (PhCCl) to bridgehead alkenes adamantene and homoadamantene, respectively, producing an intermediate singlet diradical in each case, or (b) via addition of PhCCl to the diazo analogues of noradamantyl- and adamantyldiazirine. Preliminary direct dynamics calculations on adamantene + PhCCl show a high degree of recrossing (68%), indicative of a flat transition state surface. Overall, 9% of the total trajectories formed noradamantylethylene product, each proceeding via the computed singlet diradical.

A computational study of chlorocarbene additions to cyclooctyne.

Dichloro- and phenylchlorocarbene (CCl2 and PhCCl) add to cyclooctyne via a barrierless process (MP2/6-311+G*, B3LYP/6-311+G*, B3LYP/6-31G*) to yield the expected corresponding cyclopropene adducts. A three-dimensional potential energy surface (PES) for CCl2 addition to cyclooctyne (B3LYP/6-31G*) shows the formation of the cyclopropene product and also possible formation of a vinylcarbene. Residing in a shallow energy well, the vinylcarbene easily rearranges to the cyclopropene product, or to an exocyclic vinyl bicyclo[3.3.0]octane. Although the calculated three-dimensional PES indicates possible dynamic control of the cyclooctyne-chlorocarbene system through the putative formation of a vinylcarbene (in addition to the expected cyclopropene), additional calculations and preliminary experimental work show paths through the vinylcarbene to be unlikely. If the additions of chlorocarbenes to cyclooctyne are controlled by reaction dynamics, we predict that the vast majority of the reactions proceed via traditional carbene cycloaddition with only a very minor amount of products formed from the alternative pathway.

Absolute kinetics of mesitylmethylchlorocarbene reactions

Absolute rate constants were determined for reactions of mesitylmethylchlorocarbene, which affords intramolecular products derived from 1,2-H migration, 1,2-mesityl migration, and C–H insertion; at -35 or -70 °C, however, the intrusion of intermolecular channels affords azine and carbene dimer, complicating interpretations of the kin-etics.