Excess Dimethyl Acetylenedicarboxylate Research Articles

Synthesis, Structure, and Thermolysis of Tetracoordinated 1λ4,2‐Selenazetidines Bearing Two Chiral Centers at the 3‐ and 4‐Positions

ABSTRACTThe title trans and cis isomers (trans‐3 and cis‐3) were successfully synthesized as stable compounds by taking advantage of the Martin ligand. The X‐ray crystallographic analysis of trans‐3 showed that it has a distorted pseudotrigonal bipyramidal structure, and that the two phenyl groups at the 3‐ and 4‐positions are cis to each other. The thermolysis of trans‐3 in the presence of excess dimethyl acetylenedicarboxylate (DMAD) gave a mixture of the corresponding aziridines (trans‐7 and cis‐7) and cycloadducts (11a and 11b) of the azomethine ylides formed by ring opening of the aziridines with DMAD. Heating of cis‐7 and excess DMAD under the same conditions gave diastereomeric mixtures of both the aziridines and the cycloadducts, which means that the stereochemistry of the aziridine formation from the 1,2‐selenazetidine cannot be determined in this system.

Duplicated ring enlargement of 4,9-methanothia[11]annulene to 6,11-methanothia[15]annulene

3,10-Dipyrrolidinyl-4,9-methanothia[11]annulene reacts with excess dimethyl acetylenedicarboxylate (DMAD) in refluxing toluene to give ring-enlarged 6,11-methanothia[15]annulene. X-ray crystallographic analysis of the product shows two different cis,trans-dienyl parts in the ring system. Product formation possibly involves π-facial selective addition of the enamine with DMAD and torque-selective ring opening of the intermediate cyclobutenes.

Trapping evidence for the thermal cyclization of di-(o-acetylphenyl)acetylene to 3,3'-dimethyl-1,1'-biisobenzofuran

The reaction of di-(o-acetylphenyl)acetylene (1) with excess dimethyl acetylenedicarboxylate (DMAD) produced bis-DMAD adducts meso-3 and rac-3. This transformation is suggested to involve thermal rearrangement of 1 to the intermediate 3,3'-dimethyl-1,1'-biisobenzofuran (A), and subsequent Diels-Alder cycloadditions of two equivalents of DMAD to A. The isolation of trapping products meso-3 and rac-3, which contain complex polycyclic frameworks, provide strong evidence for the transient production of A, the first biisobenzofuran. An X-ray crystal structure of meso-3 was obtained.

Formation of 6,10‐Diphenyl‐Substituted Heptalene‐4,5‐dicarboxylates.

It is shown that 4,8-diphenylazulene (1) can be easily prepared from azulene by two consecutive phenylation reactions with PhLi, followed by dehydrogenation with chloranil. Similarly, a Me group can subsequently be introduced with MeLi at C(6) of 1 (Scheme 2). This methylation led not only to the expected main product, azulene 2, but also to small amounts of product 3, the structure of which has been determined by X-ray crystal-structure analysis (cf. Fig. 1). As expected, the latter product reacts with chloranil at 40° in Et2O to give 2 in quantitative yields. Vilsmeier formylation of 1 and 2 led to the formation of the corresponding azulene-1-carbaldehydes 4 and 5. Reduction of 4 and 5 with NaBH4/BF3 ⋅ OEt2 in diglyme/Et2O 1 : 1 and BF3 ⋅ OEt2, gave the 1-methylazulenes 6 and 7, respectively. In the same way was azulene 9 available from 6via Vilsmeier formylation, followed by reduction of azulene-1-carbaldehyde 8 (Scheme 3). The thermal reactions of azulenes 1, 6, and 7 with excess dimethyl acetylenedicarboxylate (ADM) in MeCN at 100° during 72 h afforded the corresponding heptalene-4,5-dicarboxylates 11, 12, and 13, respectively (Scheme 4). On the other hand, the highly substituted azulene 9 gave hardly any heptalene-4,5-dicarboxylate.

A novel electron-transfer mediated reaction leading to lepidopterene

(Anthracen-9-yl)methanamines were found to undergo single electron-transfer mediated C–N bond cleavage in the presence of excess dimethyl acetylenedicarboxylate (DMAD) in non-polar solvents leading to the formation of lepidopterene ( 4 ) and 1,2-bis(9-anthracenyl)ethane ( 3 ). The structure of lepidopterene was confirmed on the basis of NMR data and by X-ray crystallography.

Formation of 6,10‐Diphenyl‐Substituted Heptalene‐4,5‐dicarboxylates

AbstractIt is shown that 4,8‐diphenylazulene (1) can be easily prepared from azulene by two consecutive phenylation reactions with PhLi, followed by dehydrogenation with chloranil. Similarly, a Me group can subsequently be introduced with MeLi at C(6) of 1 (Scheme 2). This methylation led not only to the expected main product, azulene 2, but also to small amounts of product 3, the structure of which has been determined by X‐ray crystal‐structure analysis (cf. Fig. 1). As expected, the latter product reacts with chloranil at 40° in Et2O to give 2 in quantitative yields. Vilsmeier formylation of 1 and 2 led to the formation of the corresponding azulene‐1‐carbaldehydes 4 and 5. Reduction of 4 and 5 with NaBH4/BF3 ⋅ OEt2 in diglyme/Et2O 1 : 1 and BF3 ⋅ OEt2, gave the 1‐methylazulenes 6 and 7, respectively. In the same way was azulene 9 available from 6 via Vilsmeier formylation, followed by reduction of azulene‐1‐carbaldehyde 8 (Scheme 3). The thermal reactions of azulenes 1, 6, and 7 with excess dimethyl acetylenedicarboxylate (ADM) in MeCN at 100° during 72 h afforded the corresponding heptalene‐4,5‐dicarboxylates 11, 12, and 13, respectively (Scheme 4). On the other hand, the highly substituted azulene 9 gave hardly any heptalene‐4,5‐dicarboxylate.

Synthesis and characterisation of second-generation metallodithiolene complexes of the type [Tp*ME(dithiolene)](M = Mo, W; E = O, S) and a novel ‘organoscorpionate’ complex of tungsten

Paramagnetic, chalcogenido-M(v) dithiolene complexes, [Tp*ME{S2C2(CO2Me)2}][M=Mo, E=O, S; M=W, E=O, S; Tp*=hydrotris(3,5-dimethylpyrazol-1-yl)borate] are generated in the reactions of dimethyl acetylenedicarboxylate (DMAC) and the sulfur-rich complexes NEt4[Tp*MoS(S4)] and NEt4[Tp*WS3]; the oxo complexes result from hydrolysis of the initial sulfido products. As well, a novel 'organoscorpionate' complex, [W{S2C2(CO2Me)2}{SC2(CO2Me)2-Tp*}], has been isolated from the reactions of NEt4[Tp*WS3] with excess DMAC. Complexes , and have been isolated and characterised by microanalytical, mass spectrometric, spectroscopic and (for and) X-ray crystallographic techniques. Complexes and have been partially characterised by mass spectrometry and IR and EPR spectroscopy. Six-coordinate, distorted-octahedral contains a terminal sulfido ligand (W=S=2.108(3)A), a bidentate dithiolene ligand (S-Cav=1.758 A, C=C=1.332(10)A) and a fac-tridentate Tp* ligand. Seven-coordinate contains a planar, bidentate dithiolene ligand (S-Cav=1.746 A, C=C=1.359(5)A) and a novel pentadentate 'organoscorpionate' ligand formed by the melding of DMAC, sulfido and trispyrazolylborate units. The latter is coordinated through two pyrazolyl N atoms (kappa2-N,N') and a tridentate kappa3-S,C,C' unit appended to N-beta of the third (uncoordinated) pyrazolyl group. The second-generation [Tp*ME(dithiolene)] complexes represent a refinement on first-generation [Tp*ME(arene-1,2-dithiolate)] complexes and their synthesis affords an opportunity to compare and contrast the electronic structures of true vs. pseudo-dithiolene ligands in otherwise analogous complexes.

Some Unusual Products from the Thermal Reaction of Azulenes with Dimethyl Acetylenedicarboxylate

AbstractThe thermal reaction of azulene‐1‐carbaldehydes 5 and 6 with excess dimethyl acetylenedicarboxylate (ADM) in decalin leads mainly to the formation of (1 + 1) and (1 + 2) adducts arising from the addition of ADM at the seven‐membered ring of the azulenes (cf. Schemes 2 and 4). The (1 + 2) adducts are formed in a homo‐Diels‐Alder reaction of ADM and isomeric tricyclic carbaldehydes which are derived from the primary tricyclic carbaldehydes by reversible [1s5s]‐C shifts (cf. Schemes 3 and 5). The thus formed pentacyclic carbaldehydes seem to undergo deep‐seated skeletal rearrangements (cf. Scheme 7) which result finally in the formation of the formyl‐tetrahydrocyclopenta[bc]acenaphthylene‐tetraesters 12 and 19, respectively. In other cases, e.g., azulene‐1‐carbaldehydes 7 and 8 (cf. Scheme 8), the thermal reaction with excess ADM furnishes only the already known tetracycfic (1 + 2) adducts of type anti‐26 to ‘anti’‐29. The thermal reaction of 1,3,4,8‐tetramethylazulene (9) with excess ADM in decalin resulted in the formation of two (1 + 2) and one (1 + 3) adduct in low yields (cf. Scheme 9). The latter turned out to be the 2,6‐bridged barrelene derivative 32. There are structural evidences that 32 is formed by similar pathways as the formyl‐tetrahydrocyclopenta[bc]acenaphthylene‐tetraesters (cf. Schemes 7 and 11). [2H3]Me‐Labelling experiments are in agreement with the proposed mechanisms (cf. Scheme 13).

Synthesis of the Novel Tricyclic Heterocycle, 1H-1,4,7-Triazaphenalene, Pyridine-containing Ring System: Hexamethyl 1H-1,4,7-Triazaphenalene-2,3,5,6,8,9-hexacarboxylate

The reaction of 3-amino-3-methylthio-2-cyanoacrylonitrile (1) with excess dimethyl acetylenedicarboxylate(DMAD) in the presence of potassium carbonate in dimethyI sulfoxide gave a novel tricyclic heterocycle, hexamethyl IH-1,4,7-triazaphenalene-2,3,5,6,8,9-hexacarboxylate (5). When one equivalent of DMAD was used in this reaction, dimethyl 4-amino-3-cyano-2-methylthio-pyridine-5,6-dicarboxylate (3), a key intermediate of 5, was obtained

Thermal Reaction of Azulene‐1‐carbaldehydes with Dimethyl Acetylenedicarboxylate

AbstractAzulene‐1‐carbaldehydes which have Me substituents at C(3) and C(8) and no substituent at C(6) react with excess dimethyl acetylenedicarboxylate (ADM) in decalin at 200° to yield exclusively the Diels‐Alder adduct at the seven‐membered ring (cf. Scheme 3). The corresponding 1‐carboxylates behave similarly (Scheme 4). Azulene‐1‐carbaldehydes which possess no Me substituent at C(8) (e.g. 11, 12 in Scheme 2) gave no defined products when heated with ADM in decalin. On the other hand, Me substitutents at C(2) may also assist the thermal addition of ADM at the seven‐membered ring of azulene‐1‐carbaldehydes (Scheme 6). However, in these cases the primary tricyclic adducts react with a second molecule of ADM to yield corresponding tetracyclic compounds. The new tricyclic aldehydes 16 and 17 which were obtained in up to 50% yield (Scheme 3) could quantitatively be decarbonylated with [RhCl(PPh3)3] in toluene at 140° to yield a thermally equilibrated mixture of four tricycles (Scheme 8). It was found that the thermal isomerization of these tricycles occur at temperatures as low as 0° and that at temperatures > 40° the thermal equilibrium between the four tricycles is rapidly established via [1,5]‐C shifts. The establishment of the equilibrium makes the existence of two further tricycles necessary (cf. Scheme 8). However, in the temperature range of up to 85° these two further tricycles could not be detected by 1H‐NMR. When heated in the presence of excess ADM in decalin at 180°, the ‘missing’ tricyclic forms could be evidenced by their tetracyclic trapping products ‘anti’‐45 and ‘anti’‐48, respectively (Scheme 9).

Synthesis, structure, and properties of molybdenum octahedral d 6. bis(alkyne) complexes

The complex Mo(CO) 3(CH 3CN) 3 reacts with two equiv of alkyne to give Mo(CO) 2(CH 3CN) 2(alkyne) 2. Addition of 1 equiv of NN to the latter compound yields the desired product Mo(CO) 2(NN)(alkyne) 2 (alkyne = DMAC (dimethylacetylenedicarboxylate), NN = en ( 1), pn ( 2), o-phenylenediamine ( 3), and o-NH 2CH 2py ( 4); alkyne = DEAC (diethylacetylenedicarboxylate), NN = en (5), and o-NH 2CH 2py ( 6); alkyne = PhCCCO 2Et, NN = bipy ( 7), and phen ( 8)). Compounds 1 and 2 may also be synthesized from the reaction of Mo(CO) 3(NN) 2 with excess DMAC. The structure of Mo(CO) 2(en)(DMAC) 2 ( 1) has been determined by X-ray crystallography and refined to R = 0.0235 ( R w = 0.0242) by using 3063 independent reflections with intensity ⩾ 3σ(I). The crystals were triclinic, space group P 1 ; a = 8.508(2), b = 9.587(2), and c = 13.214(3) Å; α = 78.35(2), β = 87.98(2), and γ = 78.99(2); Z = 2. The molecule adopts an octahedral geometry with the two CO groups cis to each other, the two DMAC ligands in trans positions and the remaining two sites being occupied by the nitrogen atoms of the ethylenediamine group. The orientations of the two trans alkyne ligands are mutually perpendicular with each DMAC ligand eclipsing a NMoCO vector. All the present complexes 1– 8 exhibit fluxional behavior on the NMR timescale due to the rotation of alkyne ligands around the axis through the metal center and perpendicular to the two alkyne ligands. At low temperatures, the NMR spectra of 4 and 6 reveal the presence of four different signals for each type of nuclei on the alkyne ligands. Each set of the four signals averages to only one at the fast-exchange limit. For Mo(CO) 2(phen)(PhCCCO 2Et) 2 ( 8), two conformational isomers A and B exist in solution arising from the different orientations of the PhCCCO 2Et ligands relative to the NMoCO vectors. The possible mechanisms for the observed fluixional behavior of these complexes are discussed.

Thermal Reactions of Guaiazulene and Its 3‐Methyl Derivative with Dimethyl Acetylenedicarboxylate

AbstractThe thermal reaction of 7‐isopropyl‐1,3,4‐trimethylazulene (3‐methylguaiazulene; 2) with excess dimethyl acetylenedicarboxylate (ADM) in decalin at 200° leads to the formation of the corresponding heptalene‐ (5a/5b and 6a/6b; cf. Scheme 3) and azulene‐1,2‐dicarboxylates (7 and 8, respectively). Together with small amounts of a corresponding tetracyclic compound (‘anti’‐13) these compounds are obtained via rearrangement (→ 5a/5b and 6a/6b), retro‐Diels‐Alder reaction (→ 7 and 8), and Diels‐Alder reaction with ADM (→ ‘anti’‐13) from the two primary tricyclic intermediates (14 and 15; cf. Scheme 5) which are formed by site‐selective addition of ADM to the five‐membered ring of 2. In a competing Diels‐Alder reaction, ADM is also added to the seven‐membered ring of 2, leading to the formation of the tricyclic compounds 9 and 10 and of the Diels‐Alder adducts ‘anti’‐11 and ‘anti’‐12, respectively of 9 and of a third tricyclic intermediate 16 which is at 200° in thermal equilibrium with 9 and 10 (cf. Scheme 6). The heptalenedicarboxylates 5a and 5b as well as 6a and 6b are interconverting slowly already at ambient temperature (Scheme 4). The thermal reaction of guaiazulene (1) with excess ADM in decalin at 190° leads alongside with the known heptalene‐ (3a) and azulene‐1,2‐dicarboxylates (4; cf. Schemes 2 and 7) to the formation of six tetracyclic compounds ‘anti’‐17 to ‘anti’‐21 as well as ‘syn’‐19 and small amounts of a 4:1 mixture of the tricyclic tetracarboxylates 22 and 23. The structure of the tetracyclic compounds can be traced back by a retro‐Diels‐Alder reaction to the corresponding structures of tricyclic compounds (24‐‐29; cf. Scheme 8) which are thermally interconverting by [1,5]‐C shifts at 190°. The tricyclic tetracarboxylates 22 and 23, which are slowly equilibrating already at ambient temperature, are formed by thermal addition of ADM to the seven‐membered ring of dimethyl 5‐isopropyl‐3,8‐dimethylazulene‐1,2‐dicarboxylate (7; cf. Scheme 10). Azulene 7 which is electronically deactivated by the two MeOCO groups at C(1) and C(2) shows no more thermal reactivity in the presence of ADM at the five‐membered ring (cf. Scheme 11). The tricyclic tetracarboxylates 22 and 23 react with excess ADM at 200° in a slow Diels‐Alder reaction to form the tetracyclic hexacarboxylates 32, ‘anti’‐33, and ‘anti’‐34 (cf. Schemes 10–12 as well as Scheme 13). A structural correlation of the tri‐ and tetracyclic compounds is only feasible if thermal equilibration via [1,5]‐C shifts between all six possible tricyclic tetracarboxylates (22, 23, and 35–38; cf. Scheme 13) is assumed. The tetracyclic hexacarboxylates 32, ‘anti’‐33, and ‘anti’‐34 seem to arise from the most strained tricyclic intermediates (36–38) by the Diels‐Alder reaction with ADM.

Preparation and characterization of some mixed ligand complexes of platinum(II)

The mixed ligand complexes PtX 2(ER 3)L and PtXY(ER 3)L (where ER 3 = PR 3 or AsMe 3; L = phosphine, arsine; X = Cl; Y = Cl, H or Me) have been prepared and characterized. Reaction of PtMe 2(ER 3)L with HCl yields PtMeCl(ER 3)L, in exclusively one of three possible isomeric forms. Excess tetramethyltin reacts with Pt 2Cl 2(μ-Cl) 2(PMe 2Ph) 2 giving both cis and trans Pt 2(μ-Cl) 2(PMe 2Ph) 2, as identified from the NMR spectra. Cleavage of Pt 2(μ-Cl) 2Me 2(PMe 2Ph) 2 with donor ligands such as AsPh 3, PMe 2 or pyridine, was useful as a synthetic route to the unsymmetrical methylchloro Pt II derivatives. The reaction of cis-[PtMe 2(PPh 3)(AsPh 3)] with excess dimethylacetylenedicarboxylate (DMA) yielded only one product, which was of the formula trans-[Pt{C(COOCH 3)C(COOCH 3)CH 3} 2(PPh 3)(AsPh 3)], with the alkenyl groups having the same geometry about the CC bond. The use of diethylacetylene-dicarboxylate (DEA) rather than DMA gave a similar product. However, when cis-[PtMe 2(PEt 3)(AsPh 3)] was allowed to react with DMA, two products of the formula trans-[Pt{C(COOCH 3)C(COOCH 3)CH 3} 2(PEt 3)(AsPh 3)] were obtained, with the stereochemistry of both alkenyl groups being either cis or trans.

Electrocyclic reactions of tetraenes

Abstract Conjugated tetraenes with both central double bonds of cis configuration undergo a series of thermal reactions, the observable products being markedly dependent on the nature of the terminal substituents. Dimethyl 2E,4Z,6Z,8E-decatetraene-1,10-dioate ( 16 ) was prepared and found to cyclize readily at 50° to trans dimethyl 2,4-bicyclo[4.2.0)octadiene-6,7-dicarboxylate ( 18 ). This reaction proceeds to equilibrium, and the rates and equilibrium constants at the indicated temperatures are: 3.0 × 10 -5 sec -1 −40°; 8.2 × 10 -5 sec -1 , 16.0,50°; −10.0,75°; −7.47,100° with the equilibrium favoring ( 18 ). A sample of 1,8-diphenyl-1E,3Z,5Z;7E-octatetraene ( 1 ) showed no reaction below 120°, and at 175° all trans 1,8-diphenyl-octatetraene, cis and trans stilbenes, trans -5-phenyl-6( cis -styryl)-1,3-cyclohexadiene cis -5-phenyl-6-( trans -styryl)-1,3-cyclohexadiene, and cis and trans 6,8-diphenyl-tricyclo[3.2.1.0 2.7 ]oct-3-enes were formed. At 100° in the presence of excess dimethyl acetylenedicarboxylate 1 gave dimethyl trans -3,4-diphenyltricyclo[4.2.2.0 2.5 ]deca-6,9-dien-6,7-dicarboxylate. Finally 1,4-di(1-cyclohexen-1-yl)-1,3-batadiyne, hydrogenated over a Lindlar catalyst, gave only tricyclo[10.4.0.0 6,11 ]hexadeca-1,3,5-triene.