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Chai Y, Shao Y, Wang L, Wang L. Loss of benzaldehyde in the fragmentation of protonated benzoylamines: Benzoyl cation as a hydride acceptor in the gas phase. JOURNAL OF MASS SPECTROMETRY : JMS 2017; 52:664-671. [PMID: 28708326 DOI: 10.1002/jms.3969] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/02/2017] [Revised: 07/04/2017] [Accepted: 07/12/2017] [Indexed: 06/07/2023]
Abstract
In electrospray ionization tandem mass spectrometry of protonated 1-benzoylamines (1-benzoylpiperadine, 1-benzoylmorpholine, and 1-benzoyl-4-methylpiperazine), the dominant fragmentation pathway was amide bond cleavage to form benzoyl cation and neutral amine. Meanwhile, in their fragmentations, an interesting loss of benzaldehyde (106 Da) was observed and identified to derive from hydride transfer reaction between the benzoyl cation and amine. A stepwise mechanism for loss of 106 Da (benzene and CO) could be excluded with the aid of deuterium labeling experiment. Theoretical calculations indicated that hydride transfers from amines (piperadine, morpholine, and 1-methylpiperazine) to benzoyl cation were thermodynamically permitted, and 1-methylpiperazine was the best hydride donor among the 3 amines. The mass spectrometric experimental results were consistent with the computational results. The relative abundance of the iminium cation (relative to the benzoyl cation) in the fragmentation of protonated 1-benzoyl-4-methylpiperazine was higher than that in the fragmentation of the other 2 protonated 1-benzoylamines. By comparing the fragmentations of protonated 1-benzyl-4-methylpiperazine and protonated 1-benzoyl-4-methylpiperazine and the energetics of their hydride transfer reactions, this study revealed that benzoyl cation was a hydride acceptor in the gas phase, but which was weaker than benzyl cation.
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Affiliation(s)
- Yunfeng Chai
- Tea Research Institute, Chinese Academy of Agricultural Sciences, 9 South Meiling Road, Hangzhou, 310008, China
- Department of Chemistry, Zhejiang University, Hangzhou, 310027, China
| | - Yunlong Shao
- Department of Chemistry and Chemical Engineering, Beijing University of Technology, Beijing, 100124, China
| | - Lu Wang
- College of Pharmaceutical Sciences, Zhejiang University, Hangzhou, 310058, China
| | - Lin Wang
- Department of Chemistry and Chemical Engineering, Beijing University of Technology, Beijing, 100124, China
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Basher MM, Corilo YE, Sparrapan R, Benassi M, Augusti R, Eberlin MN, Riveros JM. Exploring the intrinsic polar [4+2(+)] cycloaddition reactivity of gaseous carbosulfonium and carboxonium ions. JOURNAL OF MASS SPECTROMETRY : JMS 2012; 47:1526-1535. [PMID: 23147832 DOI: 10.1002/jms.3109] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/01/2023]
Abstract
Gas-phase reactions of model carbosulfonium ions (CH(3)-S(+)=CH(2;) CH(3)CH(2)-S(+)=CH(2) and Ph-S(+)=CH(2)) and an O-analogue carboxonium ion (CH(3)-O(+)=CH(2)) with acyclic (isoprene, 1,3-butadiene, methyl vinyl ketone) and cyclic (1,3-cyclohexadiene, thiophene, furan) conjugated dienes were systematically investigated by pentaquadrupole mass spectrometry. As corroborated by B3LYP/6-311 G(d,p) calculations, the carbosulfonium ions first react at large extents with the dienes forming adducts via simple addition. The nascent adducts, depending on their stability and internal energy, react further via two competitive channels: (1) in reactions with acyclic dienes via cyclization that yields formally [4+2(+)] cycloadducts, or (2) in reactions with the cyclic dienes via dissociation by HSR loss that yields methylenation (net CH(+) transfer) products. In great contrast to its S-analogues, CH(3)-O(+)=CH(2) (as well as C(2)H(5)-O(+)=CH(2) and Ph-O(+)=CH(2) in reactions with isoprene) forms little or no adduct and proton transfer is the dominant reaction channel. Isomerization to more acidic protonated aldehydes in the course of reaction seems to be the most plausible cause of the contrasting reactivity of carboxonium ions. The CH(2)=CH-O(+)=CH(2) ion forms an abundant [4+2(+)] cycloadduct with isoprene, but similar to the behavior of such α,β-unsaturated carboxonium ions in solution, seems to occur across the C=C bond.
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Affiliation(s)
- Muftah M Basher
- ThoMSon Mass Spectrometry Laboratory, Institute of Chemistry, University of Campinas, Campinas, SP, Brazil
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Benassi M, Eberlin MN. Absolute assignment of constitutional isomers via structurally diagnostic fragment ions: the challenging case of α- and β-acyl naphthalenes. JOURNAL OF THE AMERICAN SOCIETY FOR MASS SPECTROMETRY 2010; 21:2041-2050. [PMID: 20947371 DOI: 10.1016/j.jasms.2010.08.019] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/30/2010] [Revised: 08/24/2010] [Accepted: 08/24/2010] [Indexed: 05/30/2023]
Abstract
A general mass spectrometric method is described for the absolute assignment of α- or β-acyl naphthalenes, via which the gaseous α- and β-naphthoyl cations of m/z 155 are used as structurally diagnostic fragment ions (SDFI). These stable acylium ions are common and normally abundant fragment ions of acylnaphthalenes in general. Using a pentaquadrupole mass spectrometer, CID experiments with argon and ion/molecule reactions with 2-methyl-1,3-dioxolane, isoprene, acetonitrile and propionitrile were performed but failed to distinguish the two SDFI. Reactions with ethyl vinyl ether and several homologues as well as ethyl vinyl thioether were, however, successful. In reactions with ethyl vinyl ether, the α-SDFI form a pair of diagnostic product ions of m/z 165 and m/z 181, which are absent in the corresponding spectrum of the β-SDFI. Methyl 4-(1-naphthyl)-2,4-dioxobutanoate was used as a test molecule for this class of constitutional isomers and absolute structural assignment as an α-acyl naphthalene was correctly performed via the characterization of its α-SDFI.
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Affiliation(s)
- Mario Benassi
- Thomson Mass Spectrometry Laboratory, Chemistry Institute, University of Campinas, Campinas, Brazil
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Benassi M, Corilo YE, Uria D, Augusti R, Eberlin MN. Recognition and resolution of isomeric alkyl anilines by mass spectrometry. JOURNAL OF THE AMERICAN SOCIETY FOR MASS SPECTROMETRY 2009; 20:269-277. [PMID: 19004641 DOI: 10.1016/j.jasms.2008.10.004] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/27/2008] [Revised: 10/03/2008] [Accepted: 10/03/2008] [Indexed: 05/27/2023]
Abstract
Two MS techniques have been used to recognize and resolve a representative isomeric pair of N-alkyl and ring-alkyl substituted anilines. The first technique (1) uses MS/MS to perform ion/molecule reactions of structurally-diagnostic fragment ions (SDFI) whereas the second (2) uses traveling wave ion mobility spectrometry (TWIMS) of the pair of protonated molecules followed by on-line collision-induced dissociation (CID), that is, MS/TWIMS-CID/MS. Isomeric C(7)H(7)N(+) ions of m/z 106 (1' from 4-butylaniline and 2 from N-butylaniline) are formed as abundant fragments by 70 eV EI of the anilines, and found to function as suitable SDFI. Ions 1' and 2 display nearly identical unimolecular dissociation chemistry, but contrasting bimolecular reactivity with ethyl vinyl ether, isoprene, acrolein, and 2-methyl-1,3-dioxolane. Ion 2 forms adducts to a large extent whereas 1' is nearly inert towards all reactants tested. The intact protonated anilines are readily resolved and recognized by MS/TWIMS-CID/MS in a SYNAPT mass spectrometer (Waters Corporation, Manchester, UK). The protonated N-butyl aniline (the more compact isomer) displays shorter drift time and higher lability towards CID than its 4-butyl isomer. The general application of SDFI 1' and 2 and other homologous and analogous ions and MS/TWIMS-CID/MS for absolute recognition and resolution of isomeric families of N-alkyl and ring-alkyl mono-substituted anilines and analogues is discussed.
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Affiliation(s)
- Mario Benassi
- ThoMSon Mass Spectrometry Laboratory, Institute of Chemistry, State University of Campinas, Campinas, Brazil
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Benassi M, Moraes LAB, Cabrini LG, Dias LC, Aguilar AM, Romeiro GA, Eberlin LS, Eberlin MN. Recognition of Cyclic, Acyclic, Exocyclic, and Spiro Acetals via Structurally Diagnostic Ion/Molecule Reactions with the (CH3)2N-C+═O Acylium Ion. J Org Chem 2008; 73:5549-57. [DOI: 10.1021/jo8008269] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Affiliation(s)
- Mario Benassi
- ThoMSon Mass Spectrometry Laboratory, State University of Campinas, Campinas-SP, Brazil 13083-970, University of São Paulo, Ribeirão Preto, SP, Brazil, Synthetic Organic Chemistry Laboratory, State University of Campinas, Campinas-SP, Brazil, Federal University of São Paulo, Diadema Campus, 09972-270, Diadema, SP, Brazil, and Institute of Chemistry, Fluminense Federal University, Rio de Janeiro, RJ, Brazil
| | - Luiz Alberto B. Moraes
- ThoMSon Mass Spectrometry Laboratory, State University of Campinas, Campinas-SP, Brazil 13083-970, University of São Paulo, Ribeirão Preto, SP, Brazil, Synthetic Organic Chemistry Laboratory, State University of Campinas, Campinas-SP, Brazil, Federal University of São Paulo, Diadema Campus, 09972-270, Diadema, SP, Brazil, and Institute of Chemistry, Fluminense Federal University, Rio de Janeiro, RJ, Brazil
| | - Liliane G. Cabrini
- ThoMSon Mass Spectrometry Laboratory, State University of Campinas, Campinas-SP, Brazil 13083-970, University of São Paulo, Ribeirão Preto, SP, Brazil, Synthetic Organic Chemistry Laboratory, State University of Campinas, Campinas-SP, Brazil, Federal University of São Paulo, Diadema Campus, 09972-270, Diadema, SP, Brazil, and Institute of Chemistry, Fluminense Federal University, Rio de Janeiro, RJ, Brazil
| | - Luiz Carlos Dias
- ThoMSon Mass Spectrometry Laboratory, State University of Campinas, Campinas-SP, Brazil 13083-970, University of São Paulo, Ribeirão Preto, SP, Brazil, Synthetic Organic Chemistry Laboratory, State University of Campinas, Campinas-SP, Brazil, Federal University of São Paulo, Diadema Campus, 09972-270, Diadema, SP, Brazil, and Institute of Chemistry, Fluminense Federal University, Rio de Janeiro, RJ, Brazil
| | - Andrea M. Aguilar
- ThoMSon Mass Spectrometry Laboratory, State University of Campinas, Campinas-SP, Brazil 13083-970, University of São Paulo, Ribeirão Preto, SP, Brazil, Synthetic Organic Chemistry Laboratory, State University of Campinas, Campinas-SP, Brazil, Federal University of São Paulo, Diadema Campus, 09972-270, Diadema, SP, Brazil, and Institute of Chemistry, Fluminense Federal University, Rio de Janeiro, RJ, Brazil
| | - Gilberto A. Romeiro
- ThoMSon Mass Spectrometry Laboratory, State University of Campinas, Campinas-SP, Brazil 13083-970, University of São Paulo, Ribeirão Preto, SP, Brazil, Synthetic Organic Chemistry Laboratory, State University of Campinas, Campinas-SP, Brazil, Federal University of São Paulo, Diadema Campus, 09972-270, Diadema, SP, Brazil, and Institute of Chemistry, Fluminense Federal University, Rio de Janeiro, RJ, Brazil
| | - Livia S. Eberlin
- ThoMSon Mass Spectrometry Laboratory, State University of Campinas, Campinas-SP, Brazil 13083-970, University of São Paulo, Ribeirão Preto, SP, Brazil, Synthetic Organic Chemistry Laboratory, State University of Campinas, Campinas-SP, Brazil, Federal University of São Paulo, Diadema Campus, 09972-270, Diadema, SP, Brazil, and Institute of Chemistry, Fluminense Federal University, Rio de Janeiro, RJ, Brazil
| | - Marcos N. Eberlin
- ThoMSon Mass Spectrometry Laboratory, State University of Campinas, Campinas-SP, Brazil 13083-970, University of São Paulo, Ribeirão Preto, SP, Brazil, Synthetic Organic Chemistry Laboratory, State University of Campinas, Campinas-SP, Brazil, Federal University of São Paulo, Diadema Campus, 09972-270, Diadema, SP, Brazil, and Institute of Chemistry, Fluminense Federal University, Rio de Janeiro, RJ, Brazil
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Meurer EC, Eberlin MN. The atmospheric pressure Meerwein reaction. JOURNAL OF MASS SPECTROMETRY : JMS 2006; 41:470-6. [PMID: 16498596 DOI: 10.1002/jms.1005] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/06/2023]
Abstract
We have already shown that the in-vacuum gas-phase Meerwein reaction of (thio)acylium ions is general in nature and useful for class-selective screening of cyclic (thio)epoxides. Herein we report that this gas-phase reaction can also be performed efficiently at atmospheric pressure under both electrospray ionization (ESI) and atmospheric pressure chemical ionization (APCI) conditions. This alternative expands the range of molecules that can be reacted by gas-phase Meerwein reaction. Phenyl epoxide, thiirane, 3-methoxy-2,2-dimethyloxirane, propylene oxide, 2,2'-bioxirane, trans-1,3-diphenyl-2,3-epoxypropan-1-one, epichloridrine and propylene oxide are shown to react efficiently in both ESI and APCI conditions. Tetramethylurea (TMU) and (thio)TMU were both used as dopants, being co-injected with either toluene, acetonitrile or methanol solutions of the (thio)epoxides, with similar results. In both ESI and APCI, (thio)TMU is protonated preferentially, and these labile species dissociate promptly to yield (CH3)2N-C+=O and (CH3)2NCS+, which are the least acidic and most reactive (thio)acylium ions so far tested in the gas-phase Meerwein reaction. Under the low-energy ESI conditions set to favor both the formation of the (thio)acylium ion and ion/molecule reactions, (CH3)2NCO(S)+ react competitively with (thio)TMU to form acylated (thio)TMU and with the (thio)epoxide to form the characteristic Meerwein products. Enhanced selectivity in structural characterization or for the screening of (thio)epoxides is achieved by performing on-line collision-induced dissociation of Meerwein products, particularly for the more structurally complex (thio)epoxides.
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Affiliation(s)
- Eduardo C Meurer
- Institute of Chemistry, State University of Campinas, UNICAMP, 13083-970, Brazil
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Meurer EC, Sparrapan R, Tomazela DM, Eberlin MN, Augusti R. Cyclization reactions of acylium and thioacylium ions with isocyanates and isothiocyanates: gas phase synthesis of 3,4-dihydro-2,4-dioxo-2H-1,3,5-oxadiazinium ions. JOURNAL OF THE AMERICAN SOCIETY FOR MASS SPECTROMETRY 2005; 16:1602-7. [PMID: 16087345 DOI: 10.1016/j.jasms.2005.05.011] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/04/2005] [Revised: 05/30/2005] [Accepted: 05/30/2005] [Indexed: 05/03/2023]
Abstract
Gas-phase reactions of several acylium and thioacylium ions, that is H2C=N-C+=O, H2C=N-C+=S, O=C=N-C+=O, S=C=N-C+=O, H3C-C+=O, and (CH3)2N-C+=O, with both a model isocyanate and isothiocyanate, that is, C2H5-N=C=O and C2H5-N=C=S, were investigated using tandem-in-space pentaquadrupole mass spectrometry. In these reactions, the formation of mono- and double-addition products is observed concurrently with proton transfer products. The double-addition products are far more favored in reactions with ethyl isocyanate, whereas the reactions with ethyl isothiocyanate form, preferentially, either the mono-addition product or proton transfer products, or both. Retro-addition dominates the low-energy collision-induced dissociation of the mono- and double-addition products with reformation of the corresponding reactant ions. Ab initio calculations at Becke3LYP//6-311 + G(d,p) level indicate that cyclization is favored for the double-addition products and that products equivalent to those synthesized in solution, that is, of 3,4-dihydro-2,4-dioxo-2H-1,3,5-oxadiazinium ions and sulfur analogs, are formed.
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Affiliation(s)
- Eduardo C Meurer
- Institute of Chemistry, State University of Campinas, UNICAMP, Campinas, Brazil
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Meurer EC, Chen H, Riter LS, Cooks RG, Eberlin MN. Meerwein reaction of phosphonium ions with epoxides and thioepoxides in the gas phase. JOURNAL OF THE AMERICAN SOCIETY FOR MASS SPECTROMETRY 2004; 15:398-405. [PMID: 14998542 DOI: 10.1016/j.jasms.2003.11.006] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/11/2003] [Revised: 11/06/2003] [Accepted: 11/06/2003] [Indexed: 05/24/2023]
Abstract
Phosphonium ions are shown to undergo a gas-phase Meerwein reaction in which epoxides (or thioepoxides) undergo three-to-five-membered ring expansion to yield dioxaphospholanium (or oxathiophospholanium) ion products. When the association reaction is followed by collision-induced dissociation (CID), the oxirane (or thiirane) is eliminated, making this ion molecule reaction/CID sequence a good method of net oxygen-by-sulfur replacement in the phosphonium ions. This replacement results in a characteristic mass shift of 16 units and provides evidence for the cyclic nature of the gas-phase Meerwein product ions, while improving selectivity for phosphonium ion detection. This reaction sequence also constitutes a gas-phase route to convert phosphonium ions into their sulfur analogs. Phosphonium and related ions are important targets since they are commonly and readily formed in mass spectrometric analysis upon dissociative electron ionization of organophosphorous esters. The Meerwein reaction should provide a new and very useful method of recognizing compounds that yield these ions, which includes a number of chemical warfare agents. The Meerwein reaction proceeds by phosphonium ion addition to the sulfur or oxygen center, followed by intramolecular nucleophilic attack with ring expansion to yield the 1,3,2-dioxaphospholanium or 1,3,2-oxathiophospholanium ion. Product ion structures were investigated by CID tandem mass spectrometry (MS(2)) experiments and corroborated by DFT/HF calculations.
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Affiliation(s)
- Eduardo C Meurer
- Department of Chemistry, Purdue University, West Lafayette, Indiana 47907, USA
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Meurer EC, Sabino AA, Eberlin MN. Ionic Transacetalization with Acylium Ions: A Class-Selective and Structurally Diagnostic Reaction for Cyclic Acetals Performed under Unique Electrospray and Atmospheric Pressure Chemical Ionization In-Source Ion−Molecule Reaction Conditions. Anal Chem 2003; 75:4701-9. [PMID: 14632085 DOI: 10.1021/ac0344384] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Ionic transacetalization of cyclic acetals with the gaseous (CH3)2NCO+ acylium ion has been performed under unique in-source ion-molecule reaction (in-source IMR) conditions of electrospray (ESI) and atmospheric pressure chemical ionization (APCI). In-source IMR under ESI and APCI greatly expands the range of neutral molecules that can be brought to the gas phase to react by ionic transacetalization, a general, class-selective and structurally diagnostic reaction for cyclic acetals (Moraes, L. A. B.; Gozzo, F. C.; Vainiotalo, P.; Eberlin, M. N. J. Org. Chem. 1997, 62, 5096). Heavier, more polar, and less volatile cyclic acetals than those previously employed in quadrupole collision cells are shown to react efficiently by ionic transacetalization under the ESI and APCI in-source IMR conditions. Tetramethylurea (TMU) acts as an efficient dopant, being co-injected with the acetal in either benzene, toluene, methanol, or water/methanol solutions. Under APCI or ESI, the basic TMU dopant is protonated preferentially, and the labile protonated TMU then undergoes dissociation to (CH3)2NCO+, the least acidic and the most transacetalization-reactive acylium ion so far tested. Under the relatively high-pressure, low-energy collision conditions set to favor associative reactions, (CH3)2NCO+ reacts competitively both with TMU to form acylated TMU and with the acetal via ionic transacetalization to form the respective cyclic ionic acetals. Spectrum subtraction removes the ionic products of the dopant (TMU) self-reactions, thus providing clean ion-molecule reaction product ion mass spectra, which are used for the selective, structurally diagnostic detection of cyclic acetals. Information on ring substituents comes from characteristic mass shifts resulting from aldehyde/ketone by acylium ion replacement. Enhanced selectivity in structural characterization or chemical recognition for cyclic acetal monitoring is gained by performing on-line collision-induced dissociation via tandem mass spectrometric experiments. Most cyclic ionic acetals dissociate exclusively or nearly exclusively to re-form the reactant (CH3)2NCO+ acylium ion whereas the presence of additional functional groups with increased structural complexity tends to favor other specific but likewise selective dissociation channels.
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Lemos AB, Sparrapan R, Eberlin MN. Reactions of gaseous acylium ions with 1,3-dienes: further evidence for polar [4 + 2+] Diels-Alder cycloaddition. JOURNAL OF MASS SPECTROMETRY : JMS 2003; 38:305-314. [PMID: 12644992 DOI: 10.1002/jms.442] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/24/2023]
Abstract
A novel reaction of acylium and thioacylium ions, polar [4 + 2(+)] Diels-Alder cycloaddition with 1,3-dienes and O-heterodienes, has been systematically investigated in the gas phase (Eberlin MN, Cooks RG. J. Am. Chem. Soc. 1993; 115: 9226). This polar cycloaddition, yet without precedent in solution, likely forms cyclic 2,5-dihydropyrylium ions. Here we report the reactions of gaseous acylium ions [(CH(3))(2)N-C(+)=O, Ph-C(+)=O, (CH(3))(2)N-C(+)=S, CH(3)-C(+)=O, CH(3)CH(2)-C(+)=O, and CH(2)=CH-C(+)=O] with several 1-oxy-substituted 1,3-dienes of the general formula RO-CH=CH-C(R(1))=CH(2), which were performed to collect further evidence for cycloaddition. In reactions with 1-methoxy and 1-(trimethylsilyloxy)-1,3-butadiene, adducts are formed to a great extent, but upon collision activation they mainly undergo structurally unspecific retro-addition dissociation. In reactions with Danishefsky's diene (trans-1-methoxy-3-(trimethylsilyloxy)-1,3-butadiene), adducts are also formed to great extents, but retro-addition is no longer their major dissociation; the ions dissociate instead mainly to a common fragment, the methoxyacryl cation of m/z 85. This fragment ion is most likely formed with the intermediacy of the acyclic adduct, which isomerizes prior to dissociation by a trimethylsilyl cation shift. Theoretical calculations predict that meta cycloadducts bearing 1-methoxy and 1-trimethylsilyloxy substituents are unstable, undergoing barrierless ring opening induced by the charge-stabilizing effect of the 1-oxy substituents. In contrast, for the reactions with 1-acetoxy-1,3-butadiene, both the experimental results and theoretical calculations point to the formation of intrinsically stable cycloadducts, but the intact cycloadducts are either not observed or observed in low abundances. Both the isomeric ortho and meta cycloadducts are likely formed, but the nascent ions dissociate to great extents owing to excess internal energy. The ortho cycloadducts dissociate by ketene loss; the meta cycloadducts undergo intramolecular proton transfer to the acetoxy group followed by dissociation by acetic acid loss to yield aromatic pyrylium ions. Either or both of these dissociations, ketene and/or acetic acid loss, dominate over the otherwise favored retro-Diels-Alder alternative. The pyrylium ion products therefore constitute compelling evidence for polar [4 + 2(+)] cycloaddition since their formation can only be rationalized with the intermediacy of cyclic adducts.
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Affiliation(s)
- Aline B Lemos
- State University of Campinas, UNICAMP, Institute of Chemistry, CP 6154, 13.083-970 Campinas, SP, Brazil
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Current literature in mass spectrometry. JOURNAL OF MASS SPECTROMETRY : JMS 2002; 37:443-453. [PMID: 11948851 DOI: 10.1002/jms.251] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
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