Mass spectrometry in structural and stereochemical problems. CCXV. Behavior of phenyl-substituted .alpha.,.beta.-unsaturated ketones upon electron impact. Promotion of hydrogen rearrangement processes

Abstract

This study is concerned with the effect of phenyl substitution upon the mass spectral behavior of ,/3-unsaturated ketones as an example of a substance with three potential charge-retaining sites (carbonyl, double bond, aromatic ring). Compounds of the type C6Hs(CH2)"CH==CHCOCH3, = 2-7 (I-VI), are examined.In general, the 70-eV spectra of these compounds are dominated by peaks at m/e 91 (tropylium ion) and m/e 43 (a cleavage). At nominal 12 eV, however, lower activation energy rearrangement reactions are favored.

Hydrogen and trimethylsilyl transfers during EI mass spectral fragmentation of hydroxycarboxylic and oxocarboxylic acid trimethylsilyl derivatives

“…The capability of the trimethylsilyl group to migrate over a wide range of distances was also demonstrated in the case of semirigid or rigid molecules [5]. Recently, a significant transfer of trimethylsilyl group towards the carbonyl group was also observed during EI fragmentation of the trimethylsilyl derivatives of long-chain -hydroxycarboxylic and -dicarboxylic acids [14], showing that such migrations may also occur in the case of nonrigid structures.Hydrogen transfers between distant functionalities during EI fragmentation processes are also well known [6,15,16], for this reaction hydrogen activation is needed and is caused by groups such as keto, amino, ether, trimethylsilyloxy, as well as by chain branching and unsaturation.In the present work, which is a part of a more general study of the synergistic effects during EI mass fragmentation of polyfunctional compounds [14,[17][18][19], we describe EI mass spectral fragmentation of several hydroxycarboxylic and oxocarboxylic acid trimethylsilyl derivatives, which involves trimethylsilyl and hydrogen transfers.The characterization of such compounds appears to be of great environmental importance [20,21]. Indeed, it was previously demonstrated that autoxidative processes could induce a bias during alkenone-based paAddress reprint requests to Dr.…”

“…Hydrogen transfers between distant functionalities during EI fragmentation processes are also well known [6,15,16], for this reaction hydrogen activation is needed and is caused by groups such as keto, amino, ether, trimethylsilyloxy, as well as by chain branching and unsaturation.…”

Studies on K2CO3-Catalyzed 1,4-Addition of 1,2-Allenic Ketones with Diethyl Malonate: Controlled Selective Synthesis of β,γ-Unsaturated Enones and α-Pyrones

“…The new synthetic method has several noteworthy features: (1) for 3-mono-or disubstituted-1,2-allenyl ketones, only β,γ-unsaturated enones with an unmigrated carbon-carbon double bond were produced; (2) for 3-monosubstituted-1,2-allenyl ketones the corresponding 3 were formed with an excellent stereoselectivity (E:Z > 96:4); (3) reaction is operationally simple; and (5) commercial solvents are good enough for this reaction. Sequential Michael Addition-Carbon-Carbon Double Bond Migration-Lactonization Synthesis of r-Pyrones.…”

“…β,γ-Unsaturated enones are usually obtained indirectly by rather sophisticated long and tedious procedures. Some typical methodologies for the preparation of β,γ-unsaturated ketones are summarized as follows: (1) acylation of olefins; (2) oxidation of pent-4-en-2-ol with Corey's oxidant; (3) Zn−Ag couple-promoted reaction of allylic bromide with nitriles; and (4) oxidative cleavage of phenylselenolates . Thus, it is still highly desirable to develop new and efficient methodologies for the synthesis of β,γ-unsaturated enones.…”

(Trialkylsilyl)vinylketenes: Synthesis and Application as Diene Components in Diels−Alder Cycloadditions

“…A 50-mL, three-necked, round-bottomed flask equipped with a rubber septum, argon inlet adapter, and glass stopper was charged with HMDS (1.00 mL, 0.760 g, 4.33 mmol) in 16 mL of THF and then cooled at 0 °C while n -BuLi (2.53 M in hexane, 1.70 mL, 4.33 mmol) was added rapidly dropwise over 2 min. After 10 min, the solution was cooled at −78 °C while a solution of trans -6-phenyl-3-hexen-2-one (0.687 g, 3.94 mmol) in 12 mL of THF was added dropwise over 5 min. The reaction mixture was stirred at −78 °C for 30 min, and then 2,2,2-trifluoroethyl trifluoroacetate (TFETFA, 0.63 mL, 0.922 g, 4.70 mmol) was added in one portion.…”