Progress in the Chemistry of Allene

Abstract

oxylase reaction (carboxydismurase). The object was to find whether the C02 is attached to C-2 or C-4 of the ri bulose diphosphate (4) before cleavage into two molecules of 3-phosphoglyceric acid (5). An intramolecularly doubly labeled [2-14C-2-D]phosphoglyceric acid (5a) can be formed as well as the unlabeled acid only if the C02 is attached to C-2. Since the [14C]glycolic acid obtained from the phosphoglyceric acid exhibited an isotope effect of 2.5 on oxidation with glycolic acid oxidase, this glycolic acid must have contained D as well as 14C. i.e. the CO;? is attached to C-2 in (4). 3-Tritiated (4) reacts four to six times more slowly than the H compound in the carboxylation at pH 8.1 and 25 "C. The release of the proton appears to be the limiting step of the overall reaction 11151.In the irreversible formation of a C-H bond by proton abstraction from a solvent in which the hydrogen is partially labeled, a much smaller content of the higher hydrogen isotopes is usually found in the product than in the solvent. This is a result of the isotope effect in the cleavage of an X-H bond. where X may be 0, S, N, etc. A typical example, which has been studied both experimentally and theoretically, is the hydration of isobutylene in acidic media 11211. When this reaction is carried out in I-I20/D20 mixtures, the concentration of D in the t-butyl alcohol formed is 3.9 times lower than that in the water; the ratio for T is 7.1, and that for T in D20 is 1.9.Corresponding biochemical examples are : In the enzymatic cleavage of citrate in HOT, T is incorporated into acetyl CoA. Hydrogen is incorporated preferentially, in the ratio kH/kT = 6.7 [1221. In the cleavage of threo-D,-isocitrate to succinate and glyoxylate, an isotope effect of kH/kT = 6.5 to 13.9 is found, depending on the isocitrate concentration (2x 10-3 to 4x 10-3 M), when the reaction is carried out in a buffer solution containing tritium [1231. In the cleavage of phosphoenol pyruvate by pyruvate kinase in HOT, T is incorporated with an isotope effect kH/kT of 6.4 [Iz4]. b) I s o t o p e E f f e c t s of C a r b o nLynn and Yunkwich[971studied the isotope effect of the urease reaction (with urea having the natural 12C/13C ratio) as a function of conversion, concentration, buffer, temperature, pH, and aging of the enzyme, and found a maximum value of 2.3%. The differences of the isotope effects found for various enzyme preparations were in some cases larger than the differences found for the above variables. The isotope effect of 5 to 10% found by other authors could not be confirmed.A 14C isotope effect of an unusual magnitude was found [119] for the enzymatic oxidation of [14C]formate by formic acid dehydrogenase. The value of 1.27 at 37 "C was independent of the substrate activity, which varied between 0.8 and 100 pCi/mmole. The decarboxylation of oxalacetate to pyruvate by an enzyme from Micrococcus lysodeikticus shows no isotope effect with the I3C-labeled substrate. The Mn(n)-catalysed, non-enzymatic decarboxylation, on the other hand, gives an isotope e...

Pericyclic Reactions of Cumulenes* *This chapter is dedicated to Professor R. B. Woodward on the occasion of his 60th birthday.

“…The chemistry of these cumulenes has already been reviewed in some detail (Hanford and Sauer, 1946;Lacey, 1960;Roberts and Sharts, 1962;Wilson and Goldhamer, 1963;Fisher, 1964;Huisgen et al, 1964;Lacey, 1964;Petrov and Fedorova, 1964;Griesbaum, 1966;Mavrov and Kucherov, 1967;Taylor, 1967;Ulrich, 1967;Borrmann, 1968;Gompper, 1969;Luknitskii and Vovsi, 1969;Baldwin and Fleming, 1970;Brady, 1971;Krow, 1971;Gilchrist and Storr, 1972;Okamoto, 1972;Ghosez and Marchand-Brynaert, 1976). Our aim is to offer a critical discussion of selected cumulenes as cycloaddition partners with respect to their electronic structure.…”

Synthesis of Polyethylene Containing Allene Groups: A Simple and Efficient Route to Functional Polyethylene

“…The ethylene/NBAE copolymer bearing allene groups is a promising and attractive candidate for preparing functional polyethylene. According to the photoinduced radical reaction in small molecule allene, here we demonstrate that the allene group in copolymer can also be easily transformed into the functional group using a photoinduced radical reaction 14…”

Eight‐Step Enantioselective Total Synthesis of (−)‐Cycloclavine

“…However, little is known about the fundamental behavior of unsubstituted allene in transition‐metal‐catalyzed cyclopropanations . In addition, allene is well known to oligomerize in the presence of certain metals, and therefore its successful use in an enantioselective metal carbenoid cyclopropanation remained speculative . We were thus pleased to see that the reaction proceeded smoothly in the presence of 1 mol % of dirhodium catalyst 8 (Table , Entry 1).…”

“…[13a,b] In addition, allene is well known to oligomerize in the presence of certain metals and therefore its successful use in an enantioselective metal carbenoid cyclopropanation remained speculative. [14,15] We were thus pleased to see that the reaction proceeded smoothly in the presence of 1 mol% of dirhodium catalyst 8 ( Table 1, Entry 1). After screening several chiral variants of 8, we identified complex 9 [12] as the most promising catalyst for enantioselective conversions.…”