bluuebunny/crossref_metadata_2025_split huggingface dataset:
The (apparently disrotatory) thermal ring opening of 4‐nitro‐1‐cyclobuten‐1 ‐amines
Authors: van Eijk Peter J. S. S. , Overkempe Cor , Trompenaars Willem P. , Reinhoudt David N. , Harkema Sybolt 
Published: September 2010

AbstractA series of 4‐nitro‐1‐cyclobuten‐l‐amines 3 was isolated from the thermal (2 + 2) cycloaddition of nitro(cyclo)alkenes 1 and ynamines 2. Heating of 3a‐d yielded products corresponding with disrotatory ring opening viz. the 1,3‐dienes 6a‐d. Heating of 3e,f at 60°C gave the dienes 7a,b, as the result of a conrotatory ring opening reaction, together with the trans‐2‐nitrocyclobutenes 8a,b, as the result of a hydrogen shift in the cyclobutene ring. Upon prolonged heating at 80°C 8b was converted into the diene 7b. Treatment of 3e with acid yielded the 2‐nitrocyclobutenes 9a and 9b. The structures of 3a, 3f, 6a and 7b were elucidated by X‐ray analysis. The formation of 6a‐d is attributed to E/Z isomerization of the product, initially formed by a conrotatory ring opening.
Reaction of four‐membered cyclic nitrones with acetyl chlorideα. X‐Ray crystal structures of 2‐[(acetyloxy)amino]‐N,N‐diethyl‐2‐methyl‐4‐oxo‐3‐phenylpentanamide and 1‐acetyl‐3‐chloro‐N, N‐diethyl‐2‐methyl‐4‐methylene‐3‐phenyl‐2‐azetidinecarboxamide
Authors: van Eijk Peter J. S. S. , Trompenaars Willem P. , Reinhoudt David N. , Harkema Sybolt 
Published: September 2010

AbstractReactions of the four‐membered cyclic nitrones 1 with acetyl chloride differ strongly from those of other (cyclic) nitrones. In the presence of water, the nitrones 1 yield the 2‐[(acetyloxy)‐amino]‐N,N‐diethylalkanamides 4. The structure of 4b was confirmed by X‐ray analysis. In the absence of water, the N,N‐diethyl‐4‐methylene‐2‐azetidinecarboxamides 5 or the N,N‐diethyl‐2,3‐dihydro‐2‐azetecarboxamides 6 were obtained. X‐ray analysis elucidated the structure of 5a. Under acidic conditions, compounds 5a yielded the 2‐oxa‐5‐azabicyclo[2.1.1]hexan‐3‐one derivative 13. Acid hydrolysis of 6a gave the α‐chloroketone derivative 18 and the 2‐oxopropanamide derivative 19.
Macrocyclic receptor molecules with a pendant carboxylic acid group for the complexation of urea
Authors: Aarts Veronika M. L. J. , Grootenhuis Peter D. J. , Reinhoudt David N. , Czech Anna , Czech Bronislaw P. , Bartsch Richard A. 
Published: September 2010

AbstractThe synthesis of 5,5′‐di‐tert‐butyl‐3‐(carboxymethyl)biphenyl crown ethers and several lariat ethers with pendant carboxylic acid groups, together with the determinations of the pKa values of these crown ether carboxylic acids, are described. In addition, the complexation of urea by these crown ethers has been investigated. Both the larger‐ring biphenyl crown ethers (≥ 29 ring atoms) and lariat ethers (≥ 27 ring atoms) solubilized urea in chloroform. The data for urea complexation by the lariat ethers show that, for assistance in urea complexation, it is important for the carboxylic acid group to be located close to the macrocyclic ring. When the carboxylic acid group of the lariat ethers is located in an appropriate position, urea is complexed by 21–27% of these macrocyclic ligands, as is also the case with the biphenyl crown‐ether carboxylic acids. These results demonstrate that a pendant carboxylic acid group can assist in the complexation of a neutral molecule.
Reactivity of four‐membered cyclic nitrones in 1,3‐cycloaddition reactions. X‐Ray crystal structure of 7‐(2,6‐dichlorophenyl)‐N,N‐diethyloctahydro‐6‐methyl‐1,3‐dioxo‐2‐phenylazeto[1,2‐b]pyrrolo[3,4‐d]isoxazole‐6‐carboxamide
Authors: van Eijk Peter J. S. S. , Verboom Willem , van Veggel Frank C. J. M. , Reinhoudt David N. , Harkema Sybolt 
Published: September 2010

AbstractThe four‐membered cyclic nitrones 1 and 2 react with dimethyl acetylenedicarboxylate to give the corresponding cycloadducts 3,4. Upon reaction of 2a with phenylacetylene, the 5′‐substituted isoxazoline derivative 5 was obtained. Reaction of 2a with methyl propynoate yielded a 1:4 mixture of the 4′‐ and 5′‐cycloadductsδ, 7 and 6, respectively. Reaction of 2a‐c with N‐phenylmaleimide and of 2a with diethyl maleate yielded the corresponding azeto[1,2‐b]pyrrolo[3,4‐d]isoxazole derivatives, 8 and 9, respectively. The exclusive formation of the exo‐conformation of the cycloadducts was unequivocally proven by X‐ray analysis of 8a. Reaction of 2a with methyl 2‐propenoate (methyl acrylate) and 3‐buten‐2‐one (methyl vinyl ketone) gave regio‐ and stereoselectively the corresponding exo‐5′‐isoxazolidine cycloadducts, 10 and 11, respectively. The stereochemistry of the cycloadducts was deduced from the 1H NMR data. Both alkyne and alkene dipolarophiles approach the four‐membered cyclic nitrones from the sterically less hindered side, resulting in a (regio‐ and) stereoselective formation of the cycloadducts obtained.
Transition‐metal coordination compounds of a chelating imidazole‐thioether ligand. The molecular structure of diisothiocyanato[1,6‐bis(5‐methyl‐4‐imidazolyl)‐2,5‐dithiahexane]nickel(II)
Authors: Bouwman E. , de Gelder R. , de Graaff R. A. G. , Driessen W. L. , Reedijk J. 
Published: September 2010

AbstractThe synthesis and characterization of transition‐metal coordination compounds with the novel, tetradentate ligand 1,6‐bis(5‐methyl‐4‐imidazolyl)‐2,5‐dithiahexane (abbreviated bidhx) are described. The nitrates have the general formula M(bidhx)(NO3)2·nH2O (M = Co, Ni, Cu, Zn; n = 0 ‐ 2). With the isothiocyanate anion, monomers M(bidhx)(NCS)2 containing Co, Ni and Zn and Cu(bidhx)(NCS)(NO3) as well as a dimer Cu2(bidhx)(NCS)3 were isolated. In all compounds, bidhx acts as a tetradentate ligand with both thioether sulfurs and both imidazole nitrogens coordinating. All compounds are six‐coordinated in a distorted octahedral geometry, although, for the copper mixed‐anion compound, a five‐coordination in a square pyramidal geometry may also be possible. A single crystal of [Ni(NCS)2(bidhx)](MeOH) was used in a structure determination: monoclinic, space group C2/c, a = 13.0516(7) Å, b = 16.383(1) Å, c = 10.3758(9), Å, β = 101.095(6) deg, Z = 4 and T = 293 K. The structure was solved using heavy‐atom techniques and refined by least‐squares methods to an R value of 0.0508. The nickel ion is in a distorted octahedral environment with the two thiocyanates in a cis position. The nickel to nitrogen distances are ca. 2.04 Å; the nickel to sulfur distances are ca. 2.5 Å.
In situ nucleophilic activation in the propellane 5‐chloro‐1‐aza‐5‐silatricyclo[3.3.3.01,5]undecane and its hydrolysis in solution
Authors: Jurkschat K. , Tzschach A. , Dargatz M. , Pepermans H. , Gielen M. , Willem R. 
Published: September 2010

AbstractThe compound 5‐chloro‐1‐aza‐5‐silatricyclo[3.3.3.01,5]undecane (C9H18NSiCl) combines with water to form an association complex with the formula C9H18NSiCl·H2O. Proton NMR studies at various temperatures, concentrations and magnetic fields indicate that this compound exists in solution as an equilibrium mixture of the initial chloride and its association complex with water, a structure for which is proposed. Evidence is provided against a rigid hexacoordinate complex. The equilibrium is shown to correspond to a reversible hydrolysis of C9H18NSiCl which is nucleophilically activated by the intramolecularly coordinating nitrogen present in situ. The reverse reaction is the decomposition of the association complex C9H18NSiCl·H2O to C9H18NSiCl and free water. As a consequence, this paper presents a reversible hydrolysis of a chlorosilane interconverting two directly observable pentacoordinate species without addition of an external nucleophile, and proceeding with retention of configuration at the silicon atom. We further argue that this reaction cannot proceed through a rigid hexacoordinate octahedral intermediate, but could proceed through two non‐rigid species, the averaged dynamic behaviour of which is identical to a non‐octahedral hexacoordinate transition state.
The primary structure and some kinetic properties of phospholipase A2 from sheep pancreas
Authors: Verheij H. M. , Dijkman R. , de Haas G. H. , Raykova D. , Lenting H. B. M. 
Published: September 2010

AbstractThe complete amino acid sequence of ovine phospholipase A2 (EC 3.1.1.4) has been determined. The enzyme consists of a single polypeptide chain containing 123 amino acids, crosslinked by seven disulfide bridges, with a molecular weight of 13804. The enzyme differs at six positions from phospholipase A2 isolated from bovine pancreas1. Both enzymes show similar affinities for Ca2+ ions and hydrolyze monomeric substrates with comparable efficiency.Using monomolecular surface films as a substrate, the ovine enzyme was shown to be able to hydrolyze lipids at slightly higher surface pressures than the bovine enzyme. Direct‐binding studies showed the higher affinity of the ovine enzyme for micelles of the substrate analogue, n‐hexadecylphosphocholine.We suggest that this increased affinity is attributed to a substitution of Asn122 of the bovine enzyme for a tyrosine residue in its ovine counterpart.
Metal ion catalysis in the hydroxyalkylation of phenol with glyoxylic acid
Authors: Hoefnagel A. J. , Peters J. A. , van Bekkum H. 
Published: September 2010

AbstractThe hydroxyalkylation reaction of phenol with glyoxylic acid in aqueous medium is found to be homogeneously catalyzed by various metal ions. Catalysis with MII ions results in a reaction product with an ortho/para ratio of 0.2 to 1.1, whereas catalysis using higher valent cations, because of their ability to form mixed complexes with phenol and glyoxylic acid, affords a reaction product with an ortho/para ratio of 1.3 to 28. The catalyzed Cannizzaro reaction of glyoxylic acid was observed as a side‐reaction. Addition of a suitable inert ligand, e.g. oxalic acid or NTA, is shown to decrease the ortho/para ratio and to suppress the Cannizzaro reaction.The coordination of glyoxylic acid and its hydrate with several cations has been studied by NMR techniques and a mechanism of the catalyzed hydroxyalkylation and Cannizzaro reaction is proposed.
The crystal structure of dicyclopentadienylmercury
Authors: Fischer Bart , van Mier Guido P. M. , Boersma Jaap , van Koten Gerard , Smeets Wilberth J. J. , Spek Anthony L. 
Published: September 2010

AbstractCrystals of dicyclopentadienylmercury, Hg(η1‐C5H5)2, are tetragonal, space group I41, with unit cell dimensions a = 17.347(5)Å, c = 5.810(3)Å. The low‐temperature (100 K) crystal structure was solved using Patterson methods and subsequent difference Fourier techniques. Anisotropic full‐matrix least‐squares refinement with 1832 observed reflections and 100 parameters converged at R = 0.0385. In the solid state, dicyclopentadienylmercury consists of monomeric units in which the two cyclopentadienyl rings are covalently bonded to the mercury atom.
Single‐step conversion of aliphatic, aromatic and heteroaromatic primary amines into piperazine‐2,6‐diones
Authors: Kruse C. G. , Troost J. J. , Cohen‐Fernandes P. , van der Linden H. , van Loon J. D. 
Published: September 2010

AbstractThe development of a facile, single‐step method for the synthesis of 1,4‐disubstituted piperazine‐2,6‐diones (4) in excellent yields from the corresponding aliphatic, aromatic and heteroaromatic primary amines and iminodiacetic acids (1) is described. A possible mechanism is discussed and the presence of intermediate 6a is confirmed by high‐resolution proton NMR spectroscopy. The subsequent two‐step conversion of dione 4a into the deoxygenated 4‐unsubstituted piperazine 10 in high yield provides an attractive alternative to the currently available (hetero)arylpiperazine synthetic methods.
Photochemical reactivity of α‐phenyl β,γ‐enones. Singlet 1,3‐acyl shift, triplet aromatic di‐π‐methane (DPM) rearrangement and triplet aryl‐carbonyl bridging
Authors: Koppes Margareth J. C. M. , Beentjes Peter C. J. , Cerfontain Hans 
Published: September 2010

AbstractThe photochemistry of the series of α‐phenyl β,γ‐enones 6–10 has been studied under conditions of both direct (λ 300 nm) and triplet‐sensitized irradiation with the aim of determining the reactivity patterns of these “multi”‐chromophoric systems.Upon direct irradiation, the reactants exhibit the typical photoreactions of β,γ‐enones, viz. the 1,3‐acyl shift, affording the corresponding (E)‐ and (Z)‐5‐phenyl‐4‐hexen‐3‐ones, decarbonylation of the radicals formed by α‐cleavage and recombination of the resulting alkyl radicals and, in addition, a new type of reaction from the triplet‐excited state yielding small amounts of the corresponding acetophenones. The acetophenones are thought to be formed by initial β‐bridging between the carbonyl and the phenyl group, followed by extrusion of the C4H6 fragment from the 1,4‐ or 1,3‐oxa‐diradical.Upon sensitized irradiation, the o‐methoxy‐ and p‐cyano‐substituted reactants 9 and 10 exhibit the di‐π‐methane rearrangement, leading to mixtures of the corresponding cis‐ and trans‐1‐acetyl‐1‐methyl‐2‐phenylcyclopropanes, with quantum yields of 0.03 and 0.10, respectively. The formation of the 1,3‐AS and decarbonylation products illustrates the occurrence of α‐cleavage, whereas the acetophenones and di‐π‐methane products are formed via initial aryl‐carbonyl and aryl‐vinyl bridging, respectively.The inability of the other α‐phenyl β,γ‐enones to undergo photocyclopropanation is discussed in terms of excitation‐energy partition. In the o‐methoxy‐ and p‐cyano‐substituted reactants, the excitation energy may be predominantly concentrated in the aryl moiety in contrast to the other two systems in which the excitation energy may be mainly localized on the β,γ‐enone moiety. Subsequent triplet‐energy dissipation by a free‐rotor mechanism would then account for the stability of these systems. This was observed for (E)‐7 which, upon triplet sensitization, affords only the (Z) isomer, whereas this process is degenerate for the other substrates studied.
Intramolecular exciplex formation in jet‐cooled, bichromophoric molecules, II; A dramatic effect of the acceptor electron‐affinity
Authors: Hemant R. M. , Wegewijs B. , Verhoeven J. W. , Kunst A. G. M. , Rettschnick R. P. H. 
Published: September 2010

AbstractThe jet‐cooled fluorescence properties of two bichromophoric molecules (1 and 2), differing only in the acceptor chromophore, are compared. The barrier to exciplex formation in 1, containing a powerful cyanonaphthalene acceptor chromophore, is much lower than that in 2 which contains a less powerful naphthalene acceptor chromophore. It is thus proposed that the barrier is not only of a conformational nature, but also related to the energy required for intramolecular charge separation in the Franck‐Condon excited conformation which may then be followed by a fast, electrostatically‐driven conformational change.
The nucleophilic addition‐elimination reaction on the carbonyl group of pivaloyl chloride, S‐methyl thiopivaloate and 1‐pivaloyl‐1,2,4‐triazole in the gas phase
Authors: van der Wel H. , Bruin G. J. M. , van der Linde S. J. J. , Nibbering N. M. M. , Engberts J. B. F. N. 
Published: September 2010

AbstractThe nucleophilic addition‐elimination reaction on the carbonyl group of the substrates (CH3)3CCOCl, (CH3)3CCOSCH3 and (CH3)3CCON‐CH = N‐N = CH [(CH3)3CCOTAZ] has been studied using Fourier‐Transform Ion‐Cyclotron‐Resonance (FT‐ICR) Mass Spectrometry.The rates of reactions of (CH3)3CCOCl and (CH3)3CCOSCH3 appear to depend on the basicity of the nucleophiles with the more basic ones reacting most rapidly, while the reactions of (CH3)3CCOTAZ with various nucleophiles occur either at the collision rate for exothermic reactions or not at all for endothermic reactions.These results are for (CH3)3CCOCl and (CH3)3CCOSCH3 in agreement with a double‐well potential model having the tetrahedral structure as central energy barrier.The results for the substrate (CH3)3CCOTAZ, however, can be explained very well with a single‐well potential model, where the tetrahedral structure corresponds to an energy minimum.
The meta photocycloaddition of alkyl‐ and alkoxy‐substituted arenes to cyclopentene
Authors: de Vaal P. , Osselton E.M. , Krijnen E.S. , Lodder G. , Cornelisse J. 
Published: September 2010

AbstractThe meta photocycloaddition of alkyl‐ and alkoxy‐substituted arenes to cyclopentene has been investigated and the relative reactivity of each substituted arene towards the various modes of addition determined. The results are discussed and are shown to be compatible with a polar mechanism.
Quelques aspects de la chimie des dioxa‐ et dithia‐germoles
Authors: Lavayssière H. , Dousse G. , Satgé Et J. 
Published: September 2010

AbstractDithia‐ and dioxa‐germoles: R2Ge‐X‐CR′=CR′‐X (X = S, O), have been prepared from diorganodihalogermanes and R′(NaS)C=C(SNa)R′, 1,2‐benzenedithiol, α‐hydroxy ketones, R “(KO)C=C(OK)R” or dioxastannole and by cleavage of Ge‐N bonds of diorganobis(diethylamino)germanes by benzoin. The synthesis of spirobidithiagermoles is also reported.The thermal stability of dithiagermoles has been studied. Decomposition occurs mostly by a [3 + 2] ring opening with formation of germathiones.In the presence of tertiary amines, dioxagermoles lead to germylenes and α‐diketones through a [4 + 1] ring opening.The chemical reactivity of dithia‐ and dioxa‐germoles has been studied. Exchange reactions with dihalogenated covalent compounds occur readily leading to carbon, phosphorus and sulfur dithiole and dioxole analogs. From dichlorogermylene new stable functional cyclic germylenes are obtained and characterized.
Tetrahedral intermediates formed during the nucleophilic addition‐elimination reaction of carbonyl‐containing compounds in the gas phase. Part I
Authors: van der Wel H. , Nibbering N. M. M. 
Published: September 2010

AbstractThe possibly reversible addition‐elimination reaction between CH3 18O−, CD3O−, 18O− • and D18O− and various carbonyl‐containing substrates has been studied in the gas phase using Fourier‐Transform Ion‐Cyclotron‐Resonance (FT‐ICR) Mass Spectrometry.Reversible addition‐elimination is observed for the following nucleophile/substrate systems: CH318O− (CD3O−)/RCO2CH3 (R = CH3O, C6H5, t‐C4H9), 18O− • (H18O−)/CO2 and HO−/R′CH18O (R′ = C6H5, t‐C4H9).The results obtained are discussed in relation to the formation of tetrahedral intermediates.
Directing photoinduced charge‐separation in linked donor‐acceptor systems by molecular engineering of the bridging group
Authors: Kroon J. , Verhoeven J. W. , Oliver A. M. , Paddon‐Row M. N. 
Published: September 2010

AbstractTwo bichromophoric systems (3 and 4) are studied that contain an electron donor (D) and an electron acceptor (A) moiety interconnected by a fully rigid, saturated hydrocarbon‐bridge. In both the shortest through‐bond pathway from D to A has a length of 8 sigma‐bonds, but whereas this path has an all‐trans configuration in 3, two cis elements have been introduced in 4. Photoinduced, intramolecular electron transfer from D to A occurs more than an order of magnitude faster across the stretched all‐trans bridge in 3 than across the bent bridge in 4 notwithstanding the smaller spatial distance in the latter.
Friedel‐Crafts alkylation of pyrene in carbon disulfide; 1H NMR spectroscopy of pyrene derivatives
Authors: Rodenburg L. , de Block R. , Erkelens C. , Lugtenburg J. , Cornelisse J. 
Published: September 2010

AbstractFriedel‐Crafts alkylation of pyrene with 2,5‐dichloro‐2,5‐dimethylhexane and 2,4‐dichloro‐2,4‐dimethylpentane in carbon disulfide yields 7,7,10,10‐tetramethyl‐7,8,9,10‐tetrahydrobenzo[a]pyrene and 7J,9,9‐tetramethyl‐8,9‐dihydro‐7H‐cyclopenta[a]pyrene, respectively, both in 99% yield. Alkylation with 1,4‐dichlorobutane, followed by aromatization, yields benzo[a]pyrene in a facile two‐step synthesis in 8% yield. A mechanism is proposed which rationalizes the fact that only one ring of pyrene undergoes substitution. The 1H‐1H NMR coupling constants of the pyrene derivatives are discussed.
Organometallic complexes with chiral cyclometallated ligands. The synthesis of cycloplatinated complexes containing the (S) or (R)‐2‐NMe2C6H4CH(SiR3) (R = Me, Ph) monoanion. X‐Ray crystal and molecular structure of [PtCl[CH(SiMe3)C6H4‐2‐NMe2](Et2S)]
Authors: Wehman Erik , van Koten Gerard , Hardeman Gerard , Stam Casper H. , Pfeffer Michel 
Published: September 2010

AbstractCyclometallated platinum complexes of the monoanionic ligand 2‐NMe2C6H4CH(SiR3)− (R = Me, Ph; dmat‐SiR3−) have been synthesized via the reaction of the organolithium reagent with both [PtCl2(Et2S)2] and [PtCl2(Et2COD] (COD = 1,5‐cyclooctadiene). The 1:1 reaction of Li(dmat‐SiR3) with [PtCl2(Et2S)2] affords the mono‐alkylated platinum complexes [PtCl(dmat‐SiR3)Et2S]. The X‐ray crystal structure of one of these (R = Me) was determined. The platinum centre has a square‐planar geometry with a trans‐C‐Pt‐Cl arrangement and the chelate dmat‐SiMe3 ring has a conformation that places the bulky SiMe3 substituent out of the aryl ring plane. From the 2:1 reaction of Li(dmat‐SiR3) with [PtCl2(Et2S)2] no stable organoplatinum compound could be isolated. However with [PtCl2(Et2S)2COD] this 2:1 reaction affords complexes of [Pt(dmat‐SiR3)2COD] stoichiometry. These latter monomeric complexes contain one cyclometallated dmat‐SiR3 ligand and a COD ligand that, after having undergone an addition of the second dmat‐SiR3 ligand to one of its double bonds, is η2, η1−bound to the metal.
Asymmetric addition of methyllithium to di‐p‐tolylsulfine using chiral ligands
Authors: Rewinkel J. B. M. , Porskamp P. A. T. W. , Zwanenburg B. 
Published: September 2010

AbstractThe asymmetric addition of MeLi to di‐p‐tolylsulfine 1 in the presence of the chiral ligands (2S,2′S)‐2‐(hydroxymethyl)‐1‐[(1‐methylpyrrolidin‐2‐yl)methyl]pyrrolidine 2, (2S)‐2‐hydroxymethyl‐1‐methylpyrrolidine 4, (2S,2′S)‐2‐(methoxymethyl)‐1‐[(1‐methylpyrrolidin‐2‐yl) methyl]‐pyrrolidine 5 and (2S,2′S)‐2‐(1‐hydroxy‐1‐propylbutyl)‐1 ‐[(1‐methylpyrrolidin‐2‐yl)methyl]‐pyrrolidine 6 was investigated. The influence of the molar ratio of substrate, MeLi and ligand, of temperature and of solvents on the enantiomeric excess of the sulfoxide 3 was studied for ligand 2. The optical yield varied from 5‐55%. The highest enantiomeric excess (55%) for the sulfoxide 3 was obtained using ligand 2 (ratio sulfine 1/MeLi/ligand 2 = 1.0/6.7/4.0) in tetrahydrofuran at ‐ 78°C. The results are discussed by comparing them with the enantioselective addition of MeLi to aldehydes in the presence of the same ligands.
Syntheses, conformational analyses, X‐ray analyses and force‐field‐calculations of 7,8‐dihydrohexahelicene and 5,6‐dihydrohexahelicene
Authors: Prinsen W. J. C. , Laarhoven W. H. , Bosman W. P. , Behm H. , Beurskens P. T. 
Published: September 2010

AbstractThe photocyclization of 2‐styrylbenzo[c]phenanthrene (1) in n‐butylamine yields a mixture of hexahelicene (3) and two dihydrohexahelicenes (5 and 6). Both dihydrohexahelicenes could be isolated from the irradiation mixture as pure compounds by chromatography on a silica gel coated with R( ‐ )‐TAPA, a chiral stationary phase developed for the resolution of the enantiomers of hexahelicene (3). The NMR spectra of 5,6‐dihydrohexahelicene (5) and 7,8‐dihydrohexahelicene (6) exhibit remarkable differences in the aromatic region. These differences are attributed to the location of the alicyclic ring in the hexahelicene skeleton. The X‐ray structure analyses of the dihydrohexahelicenes 5 and 6 demonstrate that, in the crystalline state, both isomers occur in only one of two possible conformations. The NMR spectra of the two compounds lead to the conclusion that, in solution, the same conformation as in the solid state is highly preferred, although the existence of the second conformation cannot be completely excluded. Structural analyses by forcefield calculations corroborate this conclusion.