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1.
Masaki Shimoi Ilia Kevlishvili Takashi Watanabe Katsuhiro Maeda Steven J. Geib Dennis P. Curran Peng Liu Tsuyoshi Taniguchi 《Angewandte Chemie (International ed. in English)》2020,59(2):903-909
An N‐heterocyclic‐carbene‐ligated 3‐benzoborepin with a bridged structure has been synthesized by double radical trans‐hydroboration of benzo[3,4]cycloundec‐3‐ene‐1,5‐diyne with an N‐heterocyclic carbene borane. The thermal reaction of the NHC‐ligated borepin at 150 °C gives an isolable NHC‐boranorcaradiene. Experiments and density functional theory calculations support a mechanism whereby the borepin initially rearranges to a boranorcaradiene by a thermal 6π‐electrocyclic reaction. This is followed by 1,5‐boron shift to give a rearranged boranorcaradiene. This shift occurs with stereoinversion at boron through a transition state with open‐shell diradical character. This is the first example of the isolation of a boranorcaradiene from a thermal reaction of a borepin. 相似文献
2.
Butanolides and Butenolides by Intramolecular Ene-Reaction during Thermolysis of Propargyl Propiolates Gas-phase flow thermolysis of 2-butynyl propynoate ( 1 ) and 2-propynyl 2-butynoate ( 2 ) at 550° afforded 3-ethynyl-2-methyl-2-buten-4-olide ( 4 , 85%) and 2-ethynyl-3-methyl-2-buten-4-olide ( 5 , 80%), respectively. Their formation presumably entails an ene reaction between the methylacetylenic and the acetylenic functions of the diyne esters 1 and 2 to give the two methyliden-vinyliden-butanolides 10 and 11 as intermediates, followed by a [1,5]-H shift to 4 and 5 . At 400–450°, the gas phase flow thermolysis of 1 and 2 led to the dimers 16 (77%) and 17 (6%), respectively. These products resulted from the Diels-Alder dimerization of the above mentioned intermediates 10 and 11 . The regioselectivity of this dimerization is determined by a ‘head-to-head’ approach, with the double bond conjugated to the carbonyl group acting as the dienophile in both cases. The low yield of 17 from 2 is probably due to a further Diels-Alder reaction of the dimer 17 with its precursor 11 , yielding a trimer 18 (8% isolated). This process is not possible when starting with 1 , which explains the higher yield of 16 . The gas phase flow thermolysis of 2-butynyl 2-butynoate ( 3 ) at 550° afforded a mixture of four isomeric products, namely the two monocyclic ethynyl-butenolides 6 and 7 and the two bicyclic vinyl-butenolides 8 and 9 . The formations of 6–9 are also rationalizable by initial ene-reactions, in this case two alternative ones, each involving one of the two CH3 groups of 3 . This leads to two alkylidene-vinylidene-butenolides, namely 12 and 13 . A [1,5]-H shift converts 12 into 6 and 13 into 7 . A competing alternative [1,5]-H shift transforms both 12 and 13 to the triene 14 , which electrocyclizes to the cyclohexadiene 15 . The latter undergoes two alternative [1,5]-H shifts to yield 8 and 9 . 相似文献
3.
Michael Buback Holm Frauendorf Philipp Vana 《Journal of polymer science. Part A, Polymer chemistry》2004,42(17):4266-4275
Initiation by tert‐butyl peroxypivalate (TBPP), tert‐amyl peroxypivalate (TAPP), 1,1,3,3‐tetramethylbutyl peroxypivalate (TMBPP), or 1,1,2,2‐tetramethylpropyl peroxypivalate (TMPPP) of radical polymerization of methyl methacrylate in toluene solution at 90 °C was studied via polymer end‐group analysis using electrospray ionization mass spectrometry (ESI‐MS). Conclusive peak assignments allowed for measuring the type and concentration of the fragments that actually initiate macromolecular growth after thermal decomposition of these peroxypivalates. It was found that the pivaloyloxy radical moiety undergoes instantaneous decarboxylation to yield an initiating tert‐butyl radical. The alkoxy radical moiety, on the other hand, may generate, via β‐scission reaction, different types of carbon‐centered radicals (together with a ketone) or may undergo a 1,5‐H‐shift reaction, by which reaction an oxygen‐centered radical is transformed into a carbon‐centered hydroxy radical. This hydrogen shift reaction was found in case of TMBPP. Surprisingly, no evidence for initiating alkoxy radicals could be found, not even in case of initiation by TBPP, where the intermediate tert‐butoxy radical undergoes a rapid chain‐transfer reaction with the solvent toluene. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 4266–4275, 2004 相似文献
4.
Platinum‐Catalyzed Cascade Rearrangement Reaction of 1,5‐Diynyl Esters: Unusual Regioselective 1,5‐Hydride Migration
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A highly regioselective sequential 1,3‐acyloxy migration/pentannulation/1,5‐hydride migration reaction is disclosed which provides an efficient access to (E)‐2‐vinyl‐3‐oxo‐1‐methyleneindenes under neutral and mild reaction conditions. The migrated hydrogen atom was derived from an unactivated alkyl group, and the long‐range 1,5‐H shift was confirmed through related deuterium experiments. 相似文献
5.
Tatsuyoshi Ito Prof. Dr. Nobuharu Iwasawa Dr. Jun Takaya 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(29):12011-12015
An unprecedented photo-promoted skeletal rearrangement reaction of phosphine–borane frustrated Lewis pairs, o-(borylaryl)phosphines, involving cleavage of an unstrained sp2C–sp3C σ-bond is reported. The reaction realizes an efficient synthesis of cyclic phosphonium borate compounds. The reaction mechanism via a boranorcaradiene intermediate is proposed based on theoretical calculations. This work sheds light on the new photoreactivity of phosphine–borane FLPs. 相似文献
6.
Heptaleno[1,2-c]furan-6-carbaldehydes such as 8 or their thiocarbaldehyde or iminomethyl derivatives easily undergo thermal cyclization, followed by a [1,5]- H shift, to give the corresponding heptalenodifurans, thienoheptalenofurans, as well as furoheptalenopyrroles (cf. Schemes 2 and 3). Generation of the 6-acetyl derivative of 8 from the corresponding secondary alcohol 15 with 1-hydroxy-1,2-benziodoxol-3(1H)-one 1-oxide (IBX) at 0° (cf. Scheme 4) leads directly to the formation of the cyclization product 16 which, upon standing at room temperature, undergoes the [1,5]-sigmatropic H-shift to the final difuran 17 . 1-Formylheptalene-4,5-dicarboxylates such as 9 can also be cyclized thermally, followed by the [1,5]-H shift, to the corresponding 8H-heptaleno[1,10-bc]furan-5,6-dicarboxylate 11 . On thiation with Lawesson′s reagent, 9 yields directly the corresponding heptalenothiophene 13 (cf. Scheme 3). 相似文献
7.
Theoretical study about the magnetic properties of conjugated organic molecules containing borepin with π current density was carried out. 1-(2,4,6-Trimethylphenyl)borepin moiety is the center and other different groups are situated on the both β sides, which are named molecules 1-12 as theoretical model in order to establish the relationship between aromaticity and geometry variation of borepin. The optimized molecular structures of molecules 1-12 are almost keeping planar and the C2-C3 bond length of borepin turns longer from molecule 1 to molecule 12. Different borepin-annulated ring could change the conjugated effect of π-electron between borepin and these borepin-annulated rings. Moreover, the molecule presents antiaromaticity, in other words, the molecule became unstable when the C2-C3 bond length of borepin extended more than ca. 0.1417 nm. But the β position fragment and substituent groups of borepin are not affected in this case, they are still steady. However, the central borepin ring current is counteracted by symmetrical overlap of it with affiliated borepin-annulated ring current. Hence, the central borepin ring breaking would be liable to occur. These molecules have higher vertical ionization potentials(VIPs) and lower vertical electron affinities(VEAs), which suggests that these molecules could easily exist in anionic form. 相似文献
8.
Tatsuyoshi Ito Nobuharu Iwasawa Jun Takaya 《Angewandte Chemie (International ed. in English)》2020,59(29):11913-11917
An unprecedented photo‐promoted skeletal rearrangement reaction of phosphine–borane frustrated Lewis pairs, o‐(borylaryl)phosphines, involving cleavage of an unstrained sp2C–sp3C σ‐bond is reported. The reaction realizes an efficient synthesis of cyclic phosphonium borate compounds. The reaction mechanism via a boranorcaradiene intermediate is proposed based on theoretical calculations. This work sheds light on the new photoreactivity of phosphine–borane FLPs. 相似文献
9.
Lu Hao Jun‐Jie Hong Jun Zhu Prof. Zhuang‐Ping Zhan 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(18):5715-5720
A one‐pot synthesis of 3,4,5‐ and 1,3,5‐pyrazoles from tertiary propargylic alcohols and para‐tolylsulfonohydrazide has been accomplished. The pyrazoles are formed through a four‐step cascade sequence, including FeCl3‐catalyzed propargylic substitution, aza‐Meyer–Schuster rearrangement, base‐mediated 6π electrocyclization, and thermal [1,5] sigmatropic shift. In this reaction, the 3,4,5‐ and 1,3,5‐pyrazoles are produced selectively according to different substituents in the starting alcohols. 相似文献
10.
Cheong PH Morganelli P Luzung MR Houk KN Toste FD 《Journal of the American Chemical Society》2008,130(13):4517-4526
Tris(triphenylphosphinegold) oxonium tetrafluoroborate, [(Ph3PAu)3O]BF4, catalyzes the rearrangement of 1,5-allenynes to produce cross-conjugated trienes. Experimental and computational evidence shows that the ene reaction proceeds through a unique nucleophilic addition of an allene double bond to a cationic phosphinegold(I)-complexed phosphinegold(I) acetylide, followed by a 1,5-hydrogen shift. 相似文献
11.
Uncatalyzed Sigmatropic 1,5-Shift of Acyl Groups in the Thermolysis of 5-Acyl-5-methyl-1,3-cyclohexadienes Four different 5-acyl-5-methyl-1,3-cyclohexadienes 1a–d (R = COOCH3, COCH3, COC6H5, CHO) have been shown to yield mixtures of 1,3-disubstituted cyclohexadienes 2–7 and 1,3-disubstituted aromatic product 8 upon thermolysis at 150–300° in solution and at 350–500° in the gas phase in a flow system. Two reaction pathways (A and B in Scheme 2) are considered for the rearrangement of the C-Skeleton. For the ester 1a 13C-isotopic substitution shows that products arise to 75–86% through a 1,5-sigmatropic shift of the methoxycarbonyl group ( A in Scheme 2) and to 14–25% through a sequence of reaction steps involving a 1,7-H-shift reaction in an acyclic intermediate ( B in Scheme 2). For the more reactive compounds 1b–d isomerization is assumed to follow the 1,5-sigmatropic pathway exclusively ( A in Scheme 2). A kinetic study yields the following sequence for the migration tendency of acyl groups toward sigmatropic 1,5-shift: COOCH3 < COCH3 < COC6H5 < CHO. 相似文献
12.
Keitaro Senga Joze Kobe Roland K. Robins Darrell E. O'Brien 《Journal of heterocyclic chemistry》1975,12(5):893-898
The synthesis of a new series of alkylxanthine analogs containing a bridgehead nitrogen atom is reported. 1,3-Dialkylpyrazolo[1,5-a]-1,3,5-triazine-2,4-diones, were prepared by the treatment of 3-methylpyrazolo[1,5-a]-1,3,5-triazine-2,4-dione (3) with the corresponding alkyl iodide. Similarly, the reaction of 3-methyl-7-phenylpyrazolo[1,5-a]-1,3,5-dialkyl-7-phenylpyrazolo[1,5-a]-1,3,5-triazine-2,4-diones. The starting materials, 3 and 17 , were prepared via the reaction of an appropriate 3-aminopyrazole with ethoxycarbonyl isothiocyanate. Several 8-bromo derivatives were prepared by direct bromination of the 1,3-dialkylpyrazolo[1,5-a]-1,3,5-triazine-2,4-diones. 相似文献
13.
James J. Wade 《Journal of heterocyclic chemistry》1986,23(4):981-987
Two complementary procedures, each starting from 6-aminomethyluracil ( 2 ), have been used to prepare imidazo[1,5-c]pyrimidines with a variety of substituents at positions 3, 5, 6, and 7. The starting material, 2 , can be readily prepared from commercially available 6-chloromethyluracil by reaction with anhydrous ammonia. In the first procedure, 2 is acylated and then cyclodehydrated by reaction with phosphorus oxychloride to give a separable mixture of a 3-substituted 5,7-dichloroimidazo[1,5-c]pyrimidine and a 3-substituted 7-chloroimidazo[1,5-c]pyrimidin-5(6H)-one. The relative product distribution is subject to some control by the choice of the acyl substituent on the starting uracil. The resulting dichloro compounds were derivatized by reaction at the 5-position with various nucleophiles, although the 7-chloro substituent is unreactive. An alternative synthetic method proceeds from 2 in six efficient steps (protection as the phthalimide, chlorination, nucleophilic substitution, deprotection, acylation, and cyclodehydration) to 3-substituted-5,7-bis(methylthio)imidazo[1,5-c]pyrimidines. These compounds may also be derivatized by nucleophilic substitution at the 5-position. 相似文献
14.
Studies on NaI/DMSO induced retro -Michael addition (RMA) reactions on some 1,5-dicarbonyl compounds
Studies on the reaction of some 1,5-ketodiesters/1,5-diketones with NaX (X = Cl/Br/I)/DMSO have shown that under microwave/thermal
conditions, facileretro-Michael addition (RMA) reaction takes place instead of formation of the expected Krapcho products. Mechanistic studies have
shown that the NaI/DMSO system is a better system than NaCl/DMSO or NaBr/DMSO to promote the RMA pathway and DMSO is an essential
requirement. The electrophilic halide ion could be involved in this fragmentation reaction. 相似文献
15.
Mateo Alajarin Baltasar Bonillo Marta Marin-Luna Pilar Sanchez-Andrada Angel Vidal Raul-Angel Orenes 《Tetrahedron》2012,68(24):4672-4681
N-Aryl ketenimines bearing a 1,3-oxathiane function at the ortho position of the keteniminic nitrogen atom convert into spiro[1,3-oxathiane-2,4′(3′H)quinolines] under mild thermal treatment. These cyclization processes are interpreted in terms of a two-step tandem sequence involving a [1,5]-H migration followed by a 6π-electrocyclic ring closure. Moreover, the cyclization of 1,3-oxathiane-ketenimines having two different substituents at the terminal carbon atom of the ketenimine moiety provided spiroquinolines bearing two stereocenters, the C3 and C4 atoms, with moderate diastereoselectivity. A DFT study support that the mechanism of these conversions consists of a [1,5]-H shift/6π-electrocyclization sequence, in which the [1,5]-H shift is the rate-limiting step. A quantitative kinetic analysis of the cyclization of an oxathiane-ketenimine with a prochiral ketenimine function explains the sense and degree of the experimentally observed diastereoselectivity. 相似文献
16.
A DFT/B3LYP model study has been carried out on the cyclocarbopalladation and on an unusual 1,5 vinyl to aryl palladium shift which are the two first steps of a cyclocarbopalladation-Stille coupling tandem reaction of various gamma-bromopropargylic-1,2 diols with alkenyls or alkynyl stannanes catalyzed by Pd(PPh(3))(4). From the calculations, the active intermediates in the catalytic process appear to bear a single phosphine ligand, the palladium(II) center keeping in all cases a square-planar coordination pattern either through intramolecular binding of the triple bond or via an intramolecular Pd...C(phenyl) interaction. The computation of the various transition states and intermediates for the 1,5 vinyl to aryl palladium shift reveals that the intimate mechanism of this pathway corresponds to a one-step hydrogen transfer between the two negatively charged carbon atoms of the vinyl and phenyl groups. A two-step pathway involving a Pd(IV) intermediate is not likely to occur. This conclusion may apply to other 1,n-palladium shifts which have been experimentally observed in various organometallic transformations. 相似文献
17.
Quite unlike the reported facile ene reactions on the periphery of many related heterocyclic systems, similarly disposed moieties on the periphery of the chromen‐4‐one (=4H‐1‐benzopyran‐4‐one) system fail to undergo an ene reaction and display a rather unusual preference for an overall [1,5] shift of the allylic C‐atom. Thus, heating xylene solutions of 2‐(N‐allylanilino)‐, 2‐(N‐crotylanilino)‐, and 2‐(N‐cinnamylamino)‐substituted (E)‐(oxochromenyl)propenoates 9a – c and 2‐[allyl(benzyl)amino]‐, 2‐[benzyl(crotyl)amino]‐, and 2‐[benzyl(cinnamyl)amino]‐substituted (E)‐(oxochromenyl)propenoates 16a – c in a sealed tube at 220–230° leads to a [1,5] shift of the allylic moieties (allyl, crotyl, cinnamyl), which is followed by intramolecular cyclization involving the N‐atom and the ester function, to give the 3‐allyl‐3‐crotyl‐, and 3‐cinnamyl‐substituted‐1‐phenyl‐ or 1‐benzyl‐2H‐[1]benzopyrano[2,3‐b]pyridine‐2,5(1H)‐diones 10a – c and 17a – c . The anticipated carbonyl–ene reaction in the 2‐(N‐allylanilino)‐, 2‐(N‐crotylanilino)‐, 2‐(N‐cinnamylanilino)‐, 2‐[allyl(benzyl)amino]‐, 2‐[benzyl(crotyl)amino]‐, and 2‐[benzyl(cinnamyl)amino]‐substituted 4‐oxochromene‐3‐carboxaldehydes 8a – c and 15a – c is also not observed, and these molecules remain untransformed under identical conditions. No [1,5] shifts of benzyl, phenyl, or methyl groups are observed, even in the absence of allylic moieties, though facile [1,5]‐H shift occurs in 2‐(benzylamino)‐ and 2‐(phenylamino)‐substituted (E)‐(oxochromenyl)propenoates 23a , b , which is followed by a similar intramolecular cyclization leading to the 2H‐[1]benzopyrano[2,3‐b]pyridine‐2,5(1H)‐diones 24a , b . 相似文献
18.
M. I. Pleshchev V. Yu. Petukhova V. V. Kuznetsov D. V. Khakimov T. S. Pivina Yu. V. Nelyubina N. N. Makhova 《Russian Chemical Bulletin》2013,62(4):1066-1075
A new metathesis reaction of azomethine imines is found. Catalytic or thermal diaziridine ring opening of 6-aryl-1,5-diazabicyclo[3.1.0]hexanes leads to azomethine imines reacting further with het(aryl)methylidenemalononitriles to give in situ new azomethine imines inaccessible by common synthetic methods. New azomethine imines are detected as pyrazolines formed via a 1,4-H shift and trapped by the [3+2] cycloaddition with various dipolarophiles to yield 1,5-diazabicyclo[3.3.0]octane derivatives bearing pharmacophoric heterocycles, e.g. furan, nitrofuran, thiophene, and indole. The best results are achieved in the Et2O·BF3-catalyzed reactions in ionic liquids. 相似文献
19.
Prof. Mateo Alajarin Dr. Baltasar Bonillo Marta Marin‐Luna Dr. Pilar Sanchez‐Andrada Prof. Angel Vidal 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(47):16093-16103
A series of 2‐(1,3‐dioxolan‐2‐yl)phenylallenes that contained a range of substituents (alkyl, aryl, phosphinyl, alkoxycarbonyl, sulfonyl) at the cumulenic C3 position were prepared by using a diverse range of synthetic strategies and converted into their respective 1‐(2‐hydroxy)‐ethoxy‐2‐substituted naphthalenes by smooth thermal activation in toluene solution. Electron‐withdrawing groups at the C3 position accelerated these tandem processes, which consisted of 1) an initial hydride‐like [1,5]‐H shift of the acetalic H atom onto the central cumulene carbon atom; 2) a subsequent 6π‐electrocyclic ring‐closure of the resulting reactive ortho‐xylylenes; and 3) a final aromatization step with concomitant ring‐opening of the 1,3‐dioxolane fragment. If the 1,3‐dioxolane ring of the starting allenes was replaced by a dimethoxymethyl group, the reactions led to mixtures of two disubstituted naphthalenes, which were formed by the migration of either the acetalic H atom or the methoxy group, with the latter migration occurring to a lesser extent. Two of the final 1,2‐disubstituted naphthalenes were converted into their corresponding naphtho‐fused dioxaphosphepine or dioxepinone through an intramolecular transesterification reaction. A DFT computational study accounted for the beneficial influence of the 1,3‐dioxolane fragment on the carbon atom from which the H‐shift took place and also of the electron‐withdrawing substituents on the allene terminus. Remarkably, in the processes that contained a sulfonyl substituent, the conrotatory 6π‐electrocyclization step was of lower activation energy than the alternative disrotatory mode. 相似文献
20.
A facile and efficient synthesis of 1,5‐benzodiazepines with an arylsulfonamido substituent at C(3) is described. 1,5‐Benzodiazepine, derived from the condensation of benzene‐1,2‐diamine and diketene, reacts with an arylsulfonyl isocyanate via an enamine intermediate to produce the title compounds of potential synthetic and pharmacological interest in good yields (Scheme 1). In addition, reaction of benzene‐1,2‐diamine and diketene in the presence of benzoyl isothiocyanate leads to N‐[2‐(3‐benzoylthioureido)aryl]‐3‐oxobutanamide derivatives (Scheme 2). This reaction proceeds via an imine intermediate and ring opening of diazepine. The structures were corroborated spectroscopically (IR, 1H‐ and 13C‐NMR, and EI‐MS) and by elemental analyses. A plausible mechanism for this type of cyclization is proposed (Scheme 3). 相似文献