The flash pyrolysis of
d-glucose was investigated by the use of
13C labeling, in conjunction with GC/MS. Co-pyrolysis of uniformly labeled and unlabeled
d-glucose established the extent of ...unimolecular formation of each of the pyrolysis products. A complete set of singly labeled
d-glucose isotopologs was used to determine the origin of specific carbons within each of the pyrolysis products. The results were compared with the expected labeling patterns that arise when the cyclic Grob 1,3-diol fragmentation and the tandem alkaline pinacol rearrangement/retro-aldol fragmentation (TAPRRAF) discovered from the pyrolysis of glycerin are used to initiate breakage of the six-carbon chain of
d-glucose. The most promising rationalizations provided by this exercise are presented herein, for the formation of six C
3 and eight C
4 acyclic carbonyl-containing pyrolysis products, and for 3-cyclopentene-1,2-dione.
The flash pyrolysis of glycerin was investigated by the use of isotopic labeling with
13C, in conjunction with GC/MS analysis of the products. The formation of acetaldehyde and acrolein was shown to ...occur by unimolecular reaction. Acetaldehyde was found to be produced by at least two competing mechanisms. Mechanism “A” delivered C-2 of glycerin to the carbonyl group of acetaldehyde, whereas mechanism “B” delivered C-2 of glycerin to the methyl group of acetaldehyde. Formaldehyde was exclusively derived from C-1 or C-3 by either mechanism. The partition between the two mechanistic paths was found to be influenced by the presence of potassium salts and acids, but not by the presence of benzoyl peroxide or galvanoxyl. Mechanism “A” is postulated to be a concerted cyclic version of the Grob Fragmentation, proceeding through an intermediate which is hydrogen-bonded between the 1- and 3-hydroxyl groups to simultaneously generate enol-acetaldehyde, formaldehyde and H
2O. Mechanism “B” as favored by the presence of alkali is postulated to involve hydrogen-bonding between adjacent hydroxyl groups and to be an alkaline version of the pinacol rearrangement followed by retro-aldol fragmentation of the intermediary 3-oxopropoxide anion. These mechanistic classes are both fundamentally important, not only for their effect on glycerin, but for being able to provide numerous means of initial pyrolytic carbon–carbon bond breakage along carbohydrate carbon-chains, given the numerous 1,2,3-triol interactions that are possible. Further nomenclature is introduced to refine the distinctions among isotopomers and isotopologs (ipsomer, ipsolog, naturalomer, “nominal” isotopolog, ubiquilog), as extensions of a concept previously adopted by IUPAC.
Oxidation of 3-hydroxypiperidine with iodosylbenzene in water afforded 2-pyrrolidinone directly in good yields. The reaction probably involves oxidative Grob fragmentation yielding imino aldehyde, ...which upon hydrolysis produces 2-pyrrolidinone via a cyclization-oxidation sequence.
Ethyl (7
S)-10-hydroxy-7-methyldecanoate (
4
), a linear methyl-branched intermediate with its chiral center at C7, and with two different functional groups at the ends of the chain, has been ...synthesized from (+)-aromadendrene in nine steps. A Baeyer–Villiger oxidation and a Grob fragmentation are the key reactions in this transformation. Intermediate
4
has been applied in the synthesis of three linear methyl-branched pheromones, (i) (
R)-10-methyl-2-tridecanone, the active pheromone of the southern corn rootworm
Diabrotica undecimpunctata howardi Barber, (ii) (
S)-9-methylnonadecane, one of the sex pheromones of the cotton leafworm
Alabama argillacea, and (iii) (
meso)-13,23-dimethylpentatriacontane, the sex pheromone of the tse tse fly
Glossina pallidipes.
Graphic
Treatment of compounds 2 and 5, both from the C19-diterpenoid alkaloid deltaline 1, with 5% NaOH methanol (room temperature, 16 h) and NaOH-N,N-dimethylformamide (reflux, 10 h) led to the two novel ...skeletal rearrangement products 4 (90%) and 6 (62%), respectively, involving Wagner–Meerwein rearrangement and Grob fragmentation. Their structures were fully characteristized based on 2D NMR and HR-MS data.
2-Cyano-5-bromopiperidines, derived from the stereoselective addition of cyanide to 5-bromomethyl-1-pyrrolinium salts, underwent a Grob fragmentation by reaction with sodium hydride in ...dimethylformamide, affording unsaturated imidoyl cyanides.
N-Alkyl-2-cyano-5-bromopiperidines
2
underwent a Grob-type ring opening elimination when treated with a slight excess of sodium hydride in DMF.
Aromatic aldehydes react with ketones to produce(E)-1-aryl-1-alkenes via a tandem Aldol-Grob cleavage reaction sequence. The reaction, initiated by boron trifluoride, also produces a carboxylic acid ...fragment.
Aromatic aldehydes react with ketones in the presence of boron trifluoride to produce(E)-1-aryl-1-alkenes via a tandem Aldol-Grob cleavage reaction sequence.
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Synthesis of Novel D - Seco -Pregnenes W lfling, J nos; Magyar, Ang la; Schneider, Gyula
Monatshefte für Chemie,
10/2003, Volume:
1, Issue:
1
Journal Article
Oxidation of 3-hydroxypiperidine with iodosylbenzene in water afforded 2-pyrrolidinone directly in good yields. The reaction probably involves oxidative Grob fragmentation yielding imino aldehyde, ...which upon hydrolysis produces 2-pyrrolidinone via a cyclization–oxidation sequence.
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