- Nitroxyl radical reactions with 4-pentenyl- and cyclopropylketenes: New routes to 5-hexenyl- and cyclopropylmethyl radicals
-
4-Pentenylketenes 4a and 9 and cyclopropylketenes 3a, 13, 14 (RCH=C=O) are generated by photochemical Wolff rearrangements and observed by IR as relatively long-lived species at room temperature in hydrocarbon solvents. The reactions of these ketenes with the nitroxyl radicals tetramethylpiperidinyloxyl (TEMPO, TO?) and tetramethylisoindoline-2-oxyl (TMIO, IO?) form carboxy substituted 5-hexenyl and cyclopropylmethyl radicals which are either trapped by a second nitroxyl radical or undergo rearrangements followed by trapping. The rate constant of the reaction of 4a with TEMPO was similar to that of n-BuCH=C=O (1b), while 3a was 4.3 times more reactive, indicating cyclopropyl stabilization of the incipient radical.
- Allen,Fenwick,Henry-Riyad,Tidwell
-
p. 5759 - 5765
(2007/10/03)
-
- A new approach to the synthesis of cilastatin, an inhibitor of renal dipeptidase
-
A convenient preoarative synthesis of cilastatin, an inhibitor of renal dipeptidase used in drugs with the antibiotic imipenem, has been elaborated.The key intermediate in this synthesis is 2-amino-7-chloroheptanoic acid prepared by oxidative cleavage of cycloheptanone followed by bromination of 7-chloroheptanoyl chloride with subsequent amination of the 2-bromo-7-chloroheptanoic acid thus formed.All of the stages of the new synthesis are easily performed, as is the isolation of the intermediate products, and they do not require any organometallic reagents. - Key words: cilastatin, (R)-cysteine, 7-chloroheptanoic acid, 2-amino-7-chloro-2-heptenoic acid, 2,2-dimethylcyclopropanecarbonyl chloride; oxidation, bromination, amination, cyclopropanation.
- Vinogradov, M. G.,Kaigorodova, L. N.,Chel'tsova-Bebutova, G. V.,Gorshkova, L. S.,Starostin, E. K.,et al.
-
p. 167 - 171
(2007/10/02)
-
- Process for resolution of racemates of 2,2-dimethylcyclopropanecarboxylic acid
-
The enantiomers of 2,2-dimethylcyclopropanecarboxylic acid are separated by esterification with the hydroxy group of optically active mandelic acid methyl ester, crystallization of the diastereomeric esters and subsequent hydrolysis of the diastereomeric esters.
- -
-
-
- Menthyl 2,2-dimethylcyclopropanecarboxylate and resolution of the same
-
An ester obtained from 2,2-dimethylcyclopropanecarboxylic acid and optically active menthol, represented by the formula, STR1 is effectively resolved into diastereomers, which upon hydrolysis give optically active 2,2-dimethylcyclopropanecarboxylic acid.
- -
-
-
- Azetidines. 5. Reaction of 1,1,3,3-Tetramethyl- and 1-Benzyl-1,3,3-trimethylazetidinium Ions with Butyllithium and Phenyllithium. Deuterium Labeling as a Mechanistic Probe
-
The reactions of 1,1,3,3-tetramethylazetidinium iodide (1) and 1-benzyl-1,3,3-trimethylazetidinium bromide (7) with butyllithium and with phenyllithium were studied in ether.The products from the reaction of 1 with butyllithium were 1,3,3-trimethylpyrrolidine (2), 3,3-dimethyl-4-(methylamino)-1-butene (3), 1-(dimethylamino)-2,2-dimethylheptane (4), neopentylpyrrolidine (5), and 1-(dimethylamino)-2,2-dimethylcyclopropane (6).With phenyllithium, 1 gave 2 and 1-(dimethylamino)-2,2-dimethyl-3-phenylpropane (11).With butyllithium, 7 gave 2-phenyl-1,4,4-trimethylpyrrolidine (8), 1-benzyl-3,3-dimethylpyrrolidine (9), and 1-neopentyl-2-phenylpyrrolidine (10).The reaction of phenyllithium with 7 gave only 8 and 9.Mechanistic information was obtained by labeling 1 with deuterium in three different ways: N-methyl-d3, 2,2-d2, and N-methyl-d3-2,2-d2.A primary kinetic isotope effect of 9.4 was found for the formation of 2 from 1-N-methyl-d3.When 2 was formed from 1-2,2-d2, a secondary kinetic isotope effect of 1.17 was measured.The formation of 4 from 1-2,2-d2 was accompanied by a primary kinetic isotope effect of 4.7, suggesting a carbene intermediate.Ylide carbanions involving decomposition to a carbene carbanion in the formation of 3 and an azomethine ylide in the formation of 5 and 9 are probable intermediates.It is postulated that the azomethine ylides react with ethylene formed from the reaction of butyllithium with the solvent ether by means of a concerted (4 + 2) cycloaddition reaction.A primary kinetic isotope effect of 20 was found for the formation of pentylbenzene from dibenzyldimethylammonium bromide and butyllithium.
- Wills, Max T.,Wills, Irene E.,Dollen, Lawrence Von,Butler, Barry L.,Porter, John,Anderson, Arthur G.
-
p. 2489 - 2498
(2007/10/02)
-