Studies on the bacterial activity of cobalt(III) complexes. Part II. Cobalt(III) aminoacidato-complexes

Summary Cobalt(III) complexes of the typetrans-[Co(AA)₂(ox)] (where AA = aminoacidato, gly = glycinato, sar = sarcosinato, DL-ala = DL-alaninato, L-ala = L-alaninato; ox = oxalate); [Co(L-val)₂CO₃] and DL-[Co(en)₂sar]I₂ where L-val = L-valinato, en = ethylenediamine) have been investigated for their bacterial activity againstEscherichia coli B using well-cultured techniques on EMB agar and in minimal glucose media. The activities decrease in the order:trans-(N)(+)K[Co(sar)₂(ox)] >trans-(N)(+)K[Co(L-ala)₂(ox)] >trans-(N)(–)K[Co (gly)₂(ox)] >trans-(N)(+)K[Co(DL-ala)₂(ox)] >trans-(N)(+)K[Co(gly)₂(ox)] >trans(+)K[Co(DL-ala)₂(ox)] >trans-K[Co(L-val)₂CO₃].     

Donor-acceptor complexes in copolymerization. L. Preparation and microstructure of chlorine-containing alternating conjugated diene–acceptor monomer copolymers

Neighboring monomer units cause significant shifts in the infrared absorption peaks attributed to cis- and trans-1,4 units in conjugated diene-acceptor monomer copolymers. Conjugated diene-maleic anhydride alternating copolymers apparently have a predominantly cis-1,4-structure, while alternating diene-SO₂ copolymers have a predominantly trans-1,4 structure. Alternating copolymers of butadiene, isoprene, and pentadiene-1,3 with α-chloroacrylonitrile and methyl α-chloroacrylate, prepared in the presence of Et_1.5AlCl_1.5(EASC), have trans-1,4 unsaturation. Alternating copolymers of chloroprene with acrylonitrile, methyl acrylate, methyl methacrylate, α-chloroacrylonitrile, and methyl α-chloroacrylate prepared in the presence of EASC-VOCl₃ have trans-1,4 configuration. The reaction between chloroprene and acrylonitrile in the presence of AlCl₃ yields the cyclic Diel-Alder adduct in the dark and the alternating copolymer under ultraviolet irradiation. The equimolar, presumably alternating, copolymers of chloroprene with methyl acrylate and methyl methacrylate undergo cyclization at 205°C to a far lesser extent than theoretically calculated, to yield five and seven-membered lactones. The polymerization of chloroprene in the presence of EASC and acetonitrile yields a radical homopolymer with trans-1,4 unsaturation.     

Fluorination Reactions at a Platinum Carbene Complex: Reaction Routes to SF3, S(=O)F and Fluorido Complexes

The electron-rich Pt complex [Pt(IMes)₂] (IMes: [1,3-bis(2,4,6-trimethylphenyl)-2-imidazolinylidine]) can be used as precursor for the syntheses of a variety of fluorido ligand containing compounds. The sulfur fluoride SF₄ undergoes a rapid oxidative addition at Pt⁰ to yield trans-[Pt(F)(SF₃)(IMes)₂]. A photolytic reaction of SF₆ at [Pt(IMes)₂] in the presence of IMes gave the fluorido complexes trans-[Pt(F)₂(IMes)₂] and trans-[Pt(F)(SF₃)(IMes)₂] along with trans-[Pt(F)(SOF)(IMes)₂] and trans-[Pt(F)(IMes’)(IMes)] (IMes’: cyclometalated IMes ligand), the latter being products produced by reaction with adventitious water. trans-[Pt(F)(SOF)(IMes)₂] and trans-[Pt(F)₂(IMes)₂] were synthesized independently by treatment of [Pt(IMes)₂] with SOF₂ or XeF₂. A reaction of [Pt(IMes)₂] with a HF source gave trans-[Pt(H)(F)(IMes)₂], and an intermediate bifluorido complex trans-[Pt(H)(FHF)(IMes)₂] was identified. Compound trans-[Pt(H)(F)(IMes)₂] converts in the presence of CsF into trans-[Pt(F)(IMes’)(IMes)].     

Thermisches Verhalten von 1,2-Dipropenylbenzolen

1-cis, 2-cis-Dipropenylbenzene (cis, cis- 1 ) isomerises thermally at 215–235° with 1st order kinetics to give trans, cis- 1 and vice versa. At equilibrium 89% trans, cis- and 11% cis, cis- 1 are present. It is shown by thermal rearrangement of cis, cis-2′, 2″-d₂- 1 that the isomerisation is attributable to aromatic [1, 7a]-sigmatropic H-shifts. trans, trans- 1 rearranges thermally at 225–245° to yield 2, 3-dimethyl-1, 2-dihydronaphthalene ( 2 ). The formation of 2 can be visualized by disrotatory ring closure followed by an aromatic [1, 5s]-sigmatropic H-shift. 2 is also formed when, cis, cis- or trans, cis- 1 are heated for 153 h at 225°. Besides 2 a small amount (3%) of 1-ethyl-1, 2-dihydronaphthalene ( 5 ) is formed. The rearrangement of trans, trans- 1 and trans, trans-2′, 2″-d₂- 1 shows a secondary isotope effect k_H/k_D = 0,90.     

Stereospezifische Fragmentierungen in den Massenspektren von Cyclohexandiaminen und Bis(aminomethyl)cyclohexanen. 33. Mitteilung über massenspektrometrische Untersuchungen,,

Stereospecific Fragmentations in the Mass Spectra of Cyclohexanediamines and Bis(aminomethyl)cyclohexanes The mass spectral behaviour, especially loss of NH₃, of the six isomeric cyclohexanediamines 1--3 (cis and trans each, Scheme 1) as well as of the six isomeric bis(aminomethyl)cyclohexanes 4--6 (cis and trans each, Scheme 6) has been investigated. The cis- and trans-compounds of the 1,2-isomers 1 and 4 show very similar spectra, because of the ease of ring cleavage at C(1)–-C(2) and the similar geometrical relations in all ring conformations. The cis- and trans-compounds of both the 1,3- and 1,4-isomers 2, 3, 5 and 6 show striking differences in their mass spectra due to stereospecific elimination of NH₃ from the molecular ion.     

Transition-Metal Complexes with Bidentate Ligands Spanning trans-Positions. Part XVII. Some platinum(II) complexes with anionic ligands such as methoxide,formate, carboxylate,hydride, and borohydride,and the X-ray crystal structure of [PtHCl( )] (PP = 2,11-bis(diphenylphosphinomethyl)benzo[c]phenanthrene)

The complexes trans-[PtXY( 2 ] (X = H or Me; Y = OMe, OCHO, CO₂H, and BH₄; 2 = 2,11-bis{bis[3-(trifluoromethyl)phenyl]phosphinomethyl}benzo[c]phenanthrene) were prepared, and their decompositions to trans[PtHX( 2 )] were studied. Some binuclear hydrido-bridged complexes, e.g.[( 2 )HPt(μ-H)PtH( 2 )]⁺, were also obtained. The preparation of complexes trans-[PtHX( 28 )₂] (X = H or Me, 28 = bis[3-(trifluoromethyl)phenyl]benzylphosphine) is also reported. The X-ray crystal structure of trans-[PtHCl 1 )] ( 1 = 2,11-bis(diphenylphosphinomethyl)benzo[c]phenanthrene) was carried out.     

Untersuchungen zum elektronischen Einfluß von Organoliganden. XIII. Synthese und Charakterisierung von 2-funktionalisierten Vinylrhodoximen

Studies on the Electronic Influence of Organoligands. XIII. Synthesis and Characterization of 2-Functionalized Vinyl Rhodoximes 2-Functionalized vinyl rhodoximes [Rh(dmgH)₂ (PPh₃)cis/trans-CH = CHZ] ([Rh]? CH = CHZ) ) ( 1 ) can be prepared with a wide variation of the substituent Z (cis: OEt ( 1 a ), OPh ( 1 b ), Cl ( 1 c ), Me ( 1 j ), Ph ( 1 k ), SMe ( 1 l ), SPh ( 1 m ); trans: SPh ( 1 d ), Me ( 1 e ), Ph ( 1 f ), CMe₃ ( 1 g ), SiMe₃ ( 1 h )) by oxidative addition of XCH = CHZ and/or by nucleophilic addition of HC?CZ and Me₃SiC?CZ, respectively, to [Rh]^?. 1 a is converted to [Rh]? CH₂CHO ( 2 ) already in a weakly acid medium. 1 l is isomerized to trans-[Rh]? CH = CHSMe ( 1 n ) in the presence of acids. The complexes 1 are characterized by microanalysis and by ¹H, ¹³C and ³¹P NMR spectroscopy. The magnitude of the coupling constants ¹J(¹⁰³Rh, ³¹P) reveals only a small effect of Z on the (NMR) trans influence of the vinyl ligands CH = CHZ. The molecular structures of cis-[Rh]? CH = CHSPh ( 1 m ) and trans-[Rh]? CH = CHSPh ( 1 d ) show a distorted octahedral coordination of Rh with a mutual trans position of triphenyl-phosphine and the 2-phenylmercaptovinyl ligands. Van der Waals interactions exist between the sulfur and the equatorial dimethylglyoximato ligands in the cis complex 1 m .     

Preparation and Properties of Molybdenum and Tungsten Dinitrogen Complexes. 30.1 Syntheses of Zero-Valent Molybdenum Complexes with the DMF Ligand: The Crystal Structure of Trans-[Mo(CO)(DMF)(Ph2PCH2CH2PPh2)2]

Abstract

Treatment of trans-[Mo(N₂)₂(dpe)(dpm)] (dpe = Ph₂PCH₂CH₂PPh₂, dpm = Ph₂PCH₂PPh₂) or trans-[Mo(N₂)₂(dpe)(dpp)] (dpp = Ph₂PCH₂CH₂CH₂PPh₂) with excess DMF in benzene at reflux under Ar resulted in the formation of trans-[Mo(CO)(DMF)(dpe)(dpm)] or trans-[Mo(CO)(DMF)(dpe)(dpp)]. X-ray structural analysis of trans-[Mo(CO)(DMF)(dpe)₂] was performed using single crystals isolated as the minor product from the reaction mixture of trans-[Mo(N₂)₂(dpe)(dpp)] and DMF. Crystal data: C₅₆H₅₅O₂NP₄Mo, monoclinic, space group P2₁, a = 11.145(4), b = 23.425(5), c = 10.516(3) Å, β = 117.17(2)° V = 2442.6(13) ų, D _calcd = 1.35 g/cm³ for Z = 2. This disclosed the relatively long C O bond distance of the carbonyl ligand and the significantly short C=O bond length in the DMF ligand. When recrystallized from benzene/hexane under N₂, trans-[Mo(CO)(DMF)(dpe)(dpm)] was converted into trans-[Mo(CO)(N₂)(dpe)(dpm)].     

Syntheses of Unique Bicyclophostones and Unexpected Difference in the Reaction of Lawesson's Reagent vs. P2S5 with Cis-Bicyclophostone (1)

Abstract

The purpose of this study was to synthesize trans-l and determine the equilibriurr constant with cis-1. Oniy the synthesis¹ and x-ray structure² of the cis isomer have bcen reported. Four prior synthetic routes to make the vans isomer³ gave only cis product. For example, intrarmolecular ring closure of the cis or trains isomers of 4 (R= (CH₂)₃OH) with LiH or thermal closure of the cis or trans 4 (R= (CH₂)₂) gave only cis-1. Since both iosmers of 1,8-dioxabicyclo[4.4.0] decane are known and readily equilibrate (57% cis and 43% trans), the apparent inaccessibility of trans-1 attracted our attention. Thc preparation of trans-1 was achieved by treatment of cis-1 with Lawesson's reagent (LR) to provide cis-2. followed by oxidation with m-chloroperbenzoic acid/trifluoroacetic acid to give a 5:1 mixture of cis:trans 1, respectively. An unexpected formation of the sulfur analogue of 1 was observed on treatment of cis-1 with P₂S₅/pyridine at reflux temperatures to give a 1.6:1 mixture of cis:trans 3, respectively. Thermal quilibration of 1 at 204°C provided an equilibrium ratio of 99.5% cis and 0.5% of the trans isomer. However, equilibration of 3 at 250°C led to 82.2:17.8 ratio in favor of the cis isomr. These results are consistent with semiemperical MO calculations. The stereochemical outcome on treatment of 4 with LR was also investigated. X-ray structures for six compounds: trans-1, cis-2, cis and trans-3; cis-4 (R=Ph), and cis-5, (R = Ph) wen determined.     

Intramolecular diels-alder reactions. IX. Syntheses of N-benzylcyclolignan lactams

Four bis-unsaturated N-benzyl amides of the type where (C₂) and (C₂)' are variously trans-CH?CH and C?C groups, were synthesized and refluxed in acetic anhydride. Three of them cyclized to form N-benzylcyclolignan lactams by intramolecular Diels-Alder processes. In one case [(C₂) ? C?C, (C₂)' ? trans-CH?CH] the (C₂) unit functioned as the dienophilic moiety.     

Transition-Metal Complexes with Bidentate Ligands Spanning trans-Positions. II. Preparation and properties of complexes trans-[MX2(1)] (M = Ni,Pd and Pt; X = Cl,Br and I; 1 = 2, 11-Bis(diphenylphosphinomethyl)benzo[c]phenanthrene)

It is shown that the ligand 2,11-bis(diphenylphosphinomethyl)benzo[c]phenanthrene ( 1 ) reacts with nickel(II), palladium(II) and platinum(II) substrates giving either exclusively, or predominantly, mononuclear complexes of the type trans-[MX₂( 1 )] in which the organic ligand spans trans-positions. It is further shown that the spectroscopic properties which are mainly associated with metal and donor atoms in complexes of this type are closely related to those of the corresponding square planar complexes of the type trans-[MX₂(Ph₂PCH₂Ph)₂].     

The Radical Cation of Cyclobutene and its Photoproduct. Preliminary communication

The hitherto unknown radical cation of cyclobutene ( 2 ) has been generated in a CFCl₃ matrix by γ rays at 77 K. The coupling constants, as determined from the ESR spectrum of 2 ⁺, are 2.80 and 1.11 mT for the four CH₂ and the two CH = protons, respectively. Photo-induced ring opening of 2 ⁺ yields a radical cation which exhibits the same ESR and ENDOR spectra as those observed upon direct ionization of s-trans-buta-1, 3-diene (s-trans -1 ). The radical cation s-trans -1 ⁺, should, therefore, be the final product of this conversion.     

Transition metal complexes with bidentate ligands spanning trans-positions. IV. Preparation and properties of some rhodium and iridium complexes of 2,11-bis(diphenylphosphinomethyl)benzo [c]phenanthrene

The bidentate phosphine 2,11-bis(diphenylphosphinomethyl)benzo [c]phenanthrene ( 1 ) has been used to prepare the mononuclear, square planar complexes trans-[MX(CO)( 1 )] and trans-[M(CO)(CH₃CN)( 1 )][BF₄] (M = Rh, Ir; X = Cl, Br, I, NCS). It is found that the tendency of these complexes to form adducts with CO, O₂ and SO₂ is significantly lower than that of the corresponding Ph₃P complexes. The oxidative-addition reactions of complexes trans-[IrX (CO) ( 1 )] with hydrogen halides give the six-coordinate species [IrHX₂(CO) ( 1 )]. The complexes [IrH₂I (CO) ( 1 )] and [IrH₂L (CO) ( 1 )] [BF₄] (L = CO and CH₃CN) have been obtained from hydrogen and the corresponding substrates. The model compounds trans-[MCl (CO) (Ph₂PCH₂Ph)₂] (M = Rh, Ir), trans-[Ir (CO) (CH₃CN) (Ph₂PCH₂Ph)₂] [BF₄], [IrHCl₂(CO)(Ph₂PCH₂Ph)₂] and [IrH₂(CO)₂(Ph₂PCH₂Ph)₂] [BF₄] have been prepared and their special parameters are compared with those of the corresponding complexes of ligand 1 . The influence of the static requirements of this ligand on the chemistry of its rhodium and iridium complexes is discussed.     

Transformations of pyridine and deuteropyridine under the action of trimethallylborane and alcohols. Synthesis oftrans- andcis-2,6-dimethallyl-1,2,3,6-tetrahydropyridines and theirN-derivatives

Reductivetrans-2,6-dimethallylation of pyridine and deuteropyridine with trimethallylborane in the presence of alcohols proceeds at room temperature,i.e., under substantially milder conditions than the analogous reaction with the participation of triallylborane.trans-2,6-Di(2-methylallyl)-1,2,3,6-tetrahydropyridine (3) was obtained in a yield of 87%. When heated with trimethallylborane (130–135°C, 2.5 h), compound3 underwent isomerization tocis-2,6-di(2-methylallyl)-1,2,3,6-tetrahydropyridine (4). Hydrogenation oftrans- (3) andcis-isomers (4) yieldedtrans- andcis-2,6-diisobutylpiperidines, respectively. The heterocycles obtained wereN-functionalized by reactions with MeI, PhCH₂Cl, ethylene oxide, and perfluoropropyloxirane. The stereochemistry of thecis- andtrans-isomers (3 and4) was established based on the NMR spectra of theirN,N-dimethyl salts and the products of the reaction with ethylene oxide.trans-2,6-Dimethallyl-2,3,4,5,6-pentadeutero-1,2,3,6-tetrahydropyridine and a number of its derivatives were prepared from the complex of trimethallylborane with C₅D₅N. A probable mechanism of the reductivetrans-2,6-diallylation of pyridines with allylboranes in the presence of alcohols is discussed. This article is dedicated to Prof. W. Siebert (Heidelberg) on the occasion of his 60th birthday. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1361–1370, July, 1997.     

基于偶氮联吡啶配体的银和钴配位聚合物的构筑与性质

通过将2个4,4''-联吡啶基团用偶氮基团连接,我们合成了新的配体顺式-和反式-1,2-二（（4,4''-联吡啶）-3-氮烯）（cis-L和trans-L）,并利用trans-L与银离子和钴离子构筑了配位聚合物{[Ag₂（trans-L）（ClO₄）₂]·4CH₃CN}_n（1）和{[Co（trans-L）₂（H₂O）₂]（ClO₄）₂}_n（2）。其中1为一维梯形链,链与链之间通过π-π以及Ag…Ag相互作用堆积;2为三维无限dendrimer结构,其Co中心具有合适的氧化还原电位,在以荧光素为光敏剂的条件下,可作为光催化剂实现光解水放氢。     

Gemischtligand-Komplexe des Rheniums. VI. Darstellung und Strukturen der Rhenium?Thionitrosyl-Komplexe mer-[Re(NS)Cl2(Me2PhP)3] · CH2Cl2 und trans-[Re(NS)Cl3(Me2PhP)2]

Mixed-ligand Complexes of Rhenium. VI. Synthesis and X-Ray Structures of the Rhenium Thionitrosyl Complexes mer-[Re(NS)Cl₂(Me₂PhP)₃] · CH₂Cl₂ and trans-[Re(NS)Cl₃(Me₂PhP)₂] mer-Dichlorotris(dimethylphenylphosphine)(thionitrosyl)rhenium(I), mer-[Re(NS)Cl₂(Me₂PhP)₃], and trans-Trichlorobis(dimethylphenylphosphine)(thionitrosyl)rhenium(II), trans-[Re(NS)Cl₃(Me₂PhP)₂], are formed during the reaction of rhenium(V) mixed-ligand complexes of the general formula [ReN(Cl)(Me₂PhP)₂(R₂tcb)] with disulphur dichloride (HR₂tcb = N-(N,N-dialkylthiocarbamoyl)benzamidine). The chelating ligands are substituted during the reaction. mer-[Re(NS)Cl₂(Me₂PhP)₃] crystallizes monoclinic in the space group P2₁/n. The dimensions of the unit cell are a = 8.854(2); b = 31.295(3); c = 11.981(3) Å; β = 108.14(1)°; Z = 4. A final R value of 0.033 was achieved on the basis of 5 387 reflections with I ≥ 3σ(I). The rhenium atom is coordinated in a distorted octahedral environment. The Me₂PhP ligands are arranged meridionally cis to the linear thionitrosyl group. trans-[Re(NS)Cl₃(Me₂PhP)₂] crystallizes in the monoclinic space group C2/c with an unit cell of the dimensions a = 33.320(9); b = 8.446(1); c = 17.28(5) Å; β = 116.09(1)°, Z = 8. The R value converged at 0.026 on the basis of 5 460 independent reflections. The metal is octahedrally coordinated with the phosphine ligands in trans position to each other. The angle Re? N? S is 175.7(3)°.     

Arylsulfonylureido- und Arylsulfonylamidoacyl-Derivate von Hydroxy- und Oxocycloalkanen als potentielle Antidiabetica, 2. Mitt.

Zusammenfassung Die Umsetzung vontrans-2-Aminocyclohexanol mit Tosylcarbamoylierungsmitteln führt entweder zu Gemischen vontrans-2-Tosylureidocyclohexanol und N,O-bis-Tosylcarbamoyl-trans-2-aminocyclohexanol oder ausschließlich zum Bisderivat. Vollkommen nebenproduktfreiestrans-2-Tosylureidocyclohexanol erhält man sowohl bei der Hydrolyse des austrans-2-Aminocyclohexanol und Tosyliminodithiokohlensäuremethylester gebildeten Oxazolinderivates als auch bei der Sulfonamidolyse vontrans-2-Äthoxycarbonylaminocyclohexanol.trans-2-Tosylureidocyclohexanol kann auf zwei Wegen in dascis-Isomere umgewandelt werden.

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Arylsulfonylureido- and arylsulfonylamidoacyl derivatives of hydroxy- and oxocycloalkanes as potential antidiabetic drugs. II.

The reaction oftrans-2-aminocyclohexanol with tosylcarbamoylation reagents yields either mixtures oftrans-2-tosylureidocyclohexanol and N,O-bis-tosylcarbamoyl-trans-2-aminocyclohexanol, or exclusively the bis-derivative.trans-2-tosylureidocyclohexanol is obtained completely free of by-products both by hydrolysis of the oxazoline derivative formed fromtrans-2-aminocyclohexanol and methyl tosyliminodithiocarbonate, and by sulfonamidolysis oftrans-2-ethoxycarbonylaminocyclohexanol.trans-2-Tosylureidocyclohexanol can be converted to thecis-isomer by two routes.

     

基于偶氮联吡啶配体的银和钴配位聚合物的构筑与性质

通过将2个4,4’-联吡啶基团用偶氮基团连接,我们合成了新的配体顺式-和反式-1,2-二（（4,4’-联吡啶）-3-氮烯）（cis-L和trans-L）,并利用trans-L与银离子和钴离子构筑了配位聚合物{[Ag₂（trans-L）（ClO₄）₂]·4CH₃CN}_n（1）和{[Co（trans-L）₂（H₂O）₂]（ClO₄）₂}_n（2）。其中1为一维梯形链,链与链之间通过π-π以及Ag…Ag相互作用堆积;2为三维无限dendrimer结构,其Co中心具有合适的氧化还原电位,在以荧光素为光敏剂的条件下,可作为光催化剂实现光解水放氢。     

Semi-preparative high-performance liquid chromatographic separation of ceralure and related isomers

Summary A semi-preparative high-performance liquid chromatographic procedure on 5-m silica was developed for the isolation of gram quantities of ethyltrans-5-iodo-trans-2-methylcyclohexane-1-carboxylate (B₁) and ethyltrans-4-iodo-trans-2-methylcyclohexane-1-carboxylate (B₂) for comparative evaluation as male Mediterranean fruit fly,Ceratitis capitata, attractants and for NMR studies. This procedure can also be used analytically to determine the content of B₁ (the attractive isomer) in ceralure, the ethyl 4- and 5-iodo-trans-2-methylcyclohexane-1-carboxylate mixture. 1,1-Dimethylethylcis-5-iodo-trans-2-methylcyclohexane-1-carboxylate (A) and 1,1-dimethylethylcis-4-iodo-trans-2-methylcyclohexane-1-carboxylate (C) were isolated and converted to their ethyl esters, thus supplying the fourtrans-isomers of ceralure.     

Die thermische Umlagerung von 2-(Buta-1′,3′-dienyl)-phenolen in 2-Alkyl-2H-chromene; Beispiele für aromatische [1,7a]- und [1,5s]sigmatropische Wasserstoffverschiebungen

2-(1′-cis,3′-cis-)- and 2-(1′-cis,3′-trans-Penta-1′,3′-dienyl)-phenol (cis, cis- 4 and cis, trans- 4 , cf. scheme 1) rearrange thermally at 85–110° via [1,7 a] hydrogen shifts to yield the o-quinomethide 2 (R ? CH₃) which rapidly cyclises to give 2-ethyl-2H-chromene ( 7 ). The trans formation of cis, cis- and cis, trans- 4 into 7 is accompanied by a thermal cis, trans isomerisation of the 3′ double bond in 4. The isomerisation indicates that [1,7 a] hydrogen shifts in 2 compete with the electrocyclic ring closure of 2 . The isomeric phenols, trans, trans- and trans, cis- 4 , are stable at 85–110° but at 190° rearrange also to form 7 . This rearrangement is induced by a thermal cis, trans isomerisation of the 1′ double bond which occurs via [1, 5s] hydrogen shifts. Deuterium labelling experiments show that the chromene 7 is in equilibrium with the o-quinomethide 2 (R ? CH₃), at 210°. Thus, when 2-benzyl-2H-chromene ( 9 ) or 2-(1′-trans,3′-trans,-4′-phenyl-buta1′,3′-dienyl)-phenol (trans, trans- 6 ) is heated in diglyme solution at >200°, an equilibrium mixture of both compounds (～ 55% 9 and 45% 6 ) is obtained.