DFT study on [4+2] and [2+2] cycloadditions to [60] fullerene

The functionalisation of C₆₀ fullerene with 2,3-dimethylene-1,4-dioxane (I) and 2,5-dioxabicyclo [4.2.0]octa-1(8),6-diene (II) was investigated by the use of density functional theory calculations in terms of its energetic, structural, field emission, and electronic properties. The functionalisation of C₆₀ with I was previously reported experimentally. The I and II molecules are preferentially attached to a C—C bond shared and located between two hexagons of C₆₀ via [4+2] and [2+2] cycloadditions bearing reaction energies of ?15.9 kcal mol^?1 and ?72.4 kcal mol^?1, respectively. The HOMO-LUMO energy gap and work function of C₆₀ are significantly reduced following completion of the reactions. The field electron emission current of the C₆₀ surface will increase after functionalisation of either the I or II molecule.     

Intramolecular ketenimine-ketenimine [2 + 2] and [4 + 2] cycloadditions

Bis(ketenimines), in which the two heterocumulenic functions are placed in close proximity on a carbon skeleton to allow their mutual interaction, show a rich and not easily predictable chemistry. Intramolecular [2 + 2] or [4 + 2] cycloadditions are, respectively, observed when both ketenimine functions are supported on either ortho-benzylic or 2,2'-biphenylenic scaffolds. In addition, nitrogen-to-carbon [1,3] and [1,5] shifts of arylmethyl groups in N-arylmethyl-C,C-diphenyl ketenimines are also disclosed.     

Synthesis of trans,trans-[MoX2py4][MoX4py2], trans-[MoX2py4]Br3, and structural identification of trans,trans-[MoX2py4][MoX4py2] (X = Cl,Br; py = pyridine)

Trans,trans-[MoX₂py₄][MoX₄py₂] (X = Cl, A; Br, B; py = pyridine, C₅H₅N) are the side products of reaction of between (NH₄)₂[MoX₅ · H₂O] (X = Cl,Br) with pyridine diluted with methanol. Both trans,trans-[MoX₂py₄][MoX₄py₂] are monoclinic, P2₁/n space group, with z = 2 and: a = 12.568(1), b = 9.430(1), c = 14.952(1) Å and β = 100.81(1)° (A); a = 12.551(2), b = 9.533(2), c = 15.366(2) (Å) and β = 99.35(1) (B). Cations and anions are located on the symmetry centers and have eclipsed conformation of the trans located pyridine ligands. Average Mo? X and Mo? N (pyridine) bonds are; (cation) 2.41, 2.21 Å (A); 2.54, 2.21 Å (B); (anion) 2.44, 2.20 Å (A); 2.58, 2.20 Å (B). Anionic part of the compounds can be oxidised by bromine to trans-MoX₄py₂, which precipitates from the solution. Cation can be isolated from the solution in the form of trans-[MoX₂py₄]Br₃ (X = Cl, Br). The compounds were also characterised by chemical analysis, infrared spectroscopy and conductivity measurements.     

Synthesis of 7-azabicyclo[2.2.1]heptane and 2-oxa-4-azabicyclo[3.3.1]non-3-ene derivatives by base-promoted heterocyclization of alkyl N-(cis(trans)-3,trans(cis)-4-dibromocyclohex-1-yl)carbamates and N-(cis(trans)-3,trans(cis)-4-dibromocyclohex-1-yl)-2,2,2-trifluoroacetamides

We have studied the base-promoted heterocyclization of alkyl N-(cis(trans)-3,trans(cis)-4-dibromocyclohex-1-yl)carbamates and N-(cis(trans)-3,trans(cis)-4-dibromocyclohex-1-yl)-2,2,2-trifluoroacetamides, investigating the effect of the nitrogen protecting group and the relative configuration of the leaving group at C3 and C4 on the outcome of this reaction. We have observed that the sodium hydride-promoted heterocyclization of alkyl N-(cis-3,trans-4-dibromocyclohex-1-yl)carbamates (10, 12, 14, 16, 18) is a convenient method for the synthesis of 7-azabicyclo[2.2.1]heptane derivatives. For instance, the reaction of tert-butyl N-(cis-3,trans-4-dibromocyclohex-1-yl)carbamate (10) with sodium hydride in DMF at room temperature provides 2-bromo-7-[(tert-butoxy)carbonyl]-7-azabicyclo[2.2.1]heptane (2) (52% yield), whose t-BuOK-promoted hydrogen bromide elimination affords 7-[(tert-butoxy)carbonyl]-7-azabicyclo[2.2.1]hept-2-ene (31) in 78% yield, an intermediate in the total synthesis of epibatidine (1). However, the NaH/DMF-mediated heterocyclization of alkyl N-(trans-3,cis-4-dibromocyclohex-1-yl)carbamates (11, 13) is a more structure dependent reaction, where the nucleophilic attack of the oxygen atom of the protecting group controls the outcome of the reaction, giving rise to benzooxazolone and 2-oxa-4-azabicyclo[3.3.1]non-3-ene derivatives, respectively, from low to moderate yields, in complex reaction mixtures. Conversely, the NaH/DMF heterocyclizations of N-(cis-3,trans-4-dibromocyclohex-1-yl)-2,2,2-trifluoroacetamide (40) or N-(trans-3,cis-4-dibromocyclohex-1-yl)-2,2,2-trifluoroacetamide (42) are very clean reactions giving 7-azabicyclo[2.2.1]heptane or 2-oxa-4-azabicyclo[3.3.1]non-3-ene derivatives, respectively, in good yields. Finally, a mechanistic investigation, based on DFT calculations, has been carried out to rationalize the formation of the different adducts.     

Mechanically facilitated retro [4+2] cycloadditions

Poly(methyl acrylate)s (PMAs) of varying molecular weights were grown from a [4+2] cycloaddition adduct of maleimide with furan containing two polymerization initiators. Subjecting the corresponding PMA (>30 kDa) chains to ultrasound at 0 °C resulted in a retro [4+2] cycloaddition reaction, as observed by gel permeation chromatography (GPC) and UV-vis spectroscopy, as well as labeling of the liberated maleimide and furan moieties with appropriate chromophores featuring complementary functional groups. Similar results were obtained by sonicating analogous polymers that were grown from a thermally robust [4+2] cycloaddition adduct of maleimide with anthracene. The generation of anthracenyl species from these latter adducts allowed for the rate of the corresponding mechanically activated retro [4+2] cycloaddition reaction to be measured. No reduction in the number average molecular weight (M(n)) or liberation of the maleimide, furan, or anthracene moieties was observed (i) for polymers containing the cycloaddition adducts with M(n) < 20 kDa, (ii) for high molecular weight PMAs (M(n) > 60 kDa) featuring terminal cycloaddition adducts, or (iii) when the cycloaddition adducts were not covalently linked to a high molecular weight PMA. Collectively, these results support the notion that the aforementioned retro [4+2] cycloaddition processes were derived from a vectorially opposed mechanical force applied to adducts embedded within the polymer chains.     

Stereochemistry of addition of vinylacetylene to C2-epimeric trans -2-methyldecahydro-4-quinolones and trans-1,2-dimethyldecahydro-4-quinolones

Conclusions A study was made of the stereochemistry of the addition of vinylacetylene and butylmagnesium halide to the trans-2-methyl- and trans-1,2-dimethyldecahydro-4-quinolones, and the conformations of the vinyl-acetylenic and butyl-substituted alcohols of the decahydroquinoline series that are formed here were established.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 10, pp. 2257–2263, October, 1972.n     

Stereochemistry of the [2+4] cycloaddition of cyclopentyne

The [2+4] cycloaddition of cyclopentyne with a pair of diastereomeric 1,3-dienes is found to occur with high stereoselectivity. The results support the applicability of the principles of orbital symmetry even in the case of this exceedingly reactive dienophile.     

The intramolecular [4+2]π cycloadditions of (3-alkenyl)cyclopentadienes

The intramolecular cycloadditions of four specifically functionalised (3-alkenyl)cyclopentadienes are studied; the observed regiochemistries are in agreement with the predictions of frontier orbital theory.     

Rhodium-catalyzed intramolecular [4 + 2] cycloadditions of alkynyl halides

[reaction: see text] Cationic rhodium(I)-catalyzed intramolecular [4 + 2] cycloadditions of diene-tethered alkynyl halides were found to occur in good yields (70-87%). The halide moiety is compatible with the cycloaddition reactions, and no oxidative insertion to the alkynyl halide was observed. The halogen-containing cycloadducts could be transformed into a variety of products that are difficult or impossible to obtain via direct cycloaddition.     

Combined theoretical and computational study of interstrand DNA guanine-guanine cross-linking by trans-[Pt(pyridine)2] derived from the photoactivated prodrug trans,trans,trans-[Pt(N3)2(OH)2(pyridine)2

Molecular modeling and extensive experimental studies are used to study DNA distortions induced by binding platinum(II)-containing fragments derived from cisplatin and a new class of photoactive platinum anticancer drugs. The major photoproduct of the novel platinum(IV) prodrug trans,trans,trans-[Pt(N(3))(2)(OH)(2)(py)(2)] (1) contains the trans-{Pt(py)(2)}(2+) moiety. Using a tailored DNA sequence, experimental studies establish the possibility of interstrand binding of trans-{Pt(py)(2)}(2+) (P) to guanine N7 positions on each DNA strand. Ligand field molecular mechanics (LFMM) parameters for Pt-guanine interactions are then derived and validated against a range of experimental structures from the Cambridge Structural Database, published quantum mechanics (QM)/molecular mechanics (MM) structures of model Pt-DNA systems and additional density-functional theory (DFT) studies. Ligand field molecular dynamics (LFMD) simulation protocols are developed and validated using experimentally characterized bifunctional DNA adducts involving both an intra- and an interstrand cross-link of cisplatin. We then turn to the interaction of P with the DNA duplex dodecamer, d(5'-C(1)C(2)T(3)C(4)T(5)C(6)G(7)T(8)C(9)T(10)C(11)C(12)-3')·d(5'-G(13)G(14)A(15)G(16)A(17)C(18)G(19)A(20)G(21)A(22)G(23)G(24)-3') which is known to form a monofunctional adduct with cis-{Pt(NH(3))(2)(py)}. P coordinated to G(7) and G(19) is simulated giving a predicted bend toward the minor groove. This is widened at one end of the platinated site and deepened at the opposite end, while the P-DNA complex exhibits a global bend of ～67° and an unwinding of ～20°. Such cross-links offer possibilities for specific protein-DNA interactions and suggest possible mechanisms to explain the high potency of this photoactivated complex.     

The vibrational spectra of cis,cis-,trans,trans- and cis,trans-1,4-dichloro-1,3-butadiene

The i.r. spectra of cis,cis,trans,_trans and cis,trans-1,4-dichloro-1,3-butadiene were recorded in cyclohexane solution in the region 600-40 cm⁻¹. Raman spectra, including polarization measurements of the neat liquids were obtained. Some previously unobserved fundamentals, particularly in the low frequency region, were assigned, and a few revisions in the earlier interpretations were made.Force fields containing 21 parameters for the cis,cis and the trans,trans compounds were constructed by transferring force constants from cis- and trans-1-chloro-1,3-butadiene. By mixing the force constants from these monochlorobutadienes a 29 parameter force field was derived for the cis,trans compound. The calculated r.m.s. amplitudes of vibration and perpendicular amplitude correction coefficients are presented.     

Transition metal-catalyzed [4 + 2 + 2] cycloadditions of bicyclo[2.2.1]hepta-2,5-dienes (norbornadienes) and bicyclo[2.2.2]octa-2,5-dienes

The transition-metal-catalyzed [4 + 2 + 2] cycloadditions of norbornadienes, bicyclo[2.2.2]octa-2,5-diene, and benzobarrelene with 1,3-butadienes proceed in excellent yields using cobalt-based catalytic systems. Two key distinctions between these [4 + 2 + 2] cycloadditions and the corresponding transition-metal-catalyzed [2 + 2 +2] reactions of norbornadiene are the requirement of a bimetal catalytic system with a bisphosphine ligand for the former and exclusive regioselectivity in the [4 + 2 + 2] reaction of 2-substituted norbornadienes to produce 1-substituted adducts. These distinctions may indicate two distinct mechanisms for the [4 + 2 + 2] and [2 + 2 + 2] reactions.