(η3-allyl)palladium(II) catalysts for the addition polymerization of norbornene derivatives with functional groups

Cycloaliphatic polyolefins with functional groups were prepared by the Pd(II)-catalyzed addition polymerization of norbornene derivatives. Homo- and copolymers containing repeating units based on bicyclo[2.2.1] hept-5-en-2-ylmethyl decanoate (endo/exo-ratio = 80/20), bicyclo[2.2.1]hept-5-ene-2-carboxylic acid methyl ester (exo/endo = 80/20), bicyclo[2.2.1]hept-5-ene-2-methanol (endo/exo = 80/20), and bicyclo[2.2.1]hept-5-ene-2-carboxylic acid (100% endo) were prepared in 49–99% yields with {(η³-allyl)Pd(BF₄)} and {(η³-allyl)Pd(SbF₆)} as catalysts. The catalyst containing the hexafluoroantimonate ion was slightly more active than the tetrafluoroborate based Pd-complex.     

Photoreaction of 5-dicyanomethylenebicyclo[2.2.1]hept-2-ene

Irradiation of 5-dicyanomethylenebicyclo[2.2.1lhept-2-ene induces new types of photoreactions, i.e., unprecedented skeletal rearrangement leading to 7,7-dicyano-6-methylenebicyclo[3.1.1]hept-2-ene, and novel 1,3-carbon shifts to bicyclo[3.2.0]- and bicyclo[4.1.0]heptene.     

L'importance de la presence de l'oxygene en position-7 dans les reactions des alkylmagnesiens secondaires avec les anhydrides tricycliques pontes.

The reaction of secondary alkylmagnesium bromides with endo and exo bicyclo-[2.2.1]hept-5-ene-2,3-dicarboxylic anhydrides lead at the corresponding ketoacids whereas with the 7-oxa exo bicyclo[2.2.1]hept-5-ene-2,3 dicarboxylic anhydride produced only the monosubstituted lactones.     

Palladium-catalyzed polycyclizations of substituted dienynes: Stereoselective routes to highly complex polycycles

12-Substituted 2-bromo-1,11-dien-6-ynes were found to undergo a palladium-catalyzed biscyclization followed by a diastereospecific 6π-electrocyclic rearrangement or a Diels-Alder reaction to give substituted angularly bisanellated cyclohexadienes or polycyclic bicyclo[4.1.0]hept-2-ene derivatives containing a three-membered ring, depending on the type and pattern of substituents.     

Umsetzungen des Cyclohex-3-en-carbaldehyd-p-toluolsulfonylhydrazons

The vacuum thermolysis (80–90°) of the sodium salt of cyclohex-3-ene-carbaldehyde p-toluenesulfonylhydrazone ( 1 ) in silicone oil gave diazomethyl-cyclohex-3-ene ( 2 ). Pyrolytic and photolytic decomposition of this diazo compound 2 lead to methylenecyclohex-3-ene ( 5 ) and bicyclo [4.1.0]hept-2-ene ( 6 ) (about 3:1), while the CuCl catalyzed cleavage yielded only 5 . The postulated carbene mechanism should also apply under the direct aprotic decomposition conditions of the sodium salt of 1 in diglyme, where methylenecyclohex-3-ene and bicyclo[4.1.0]hept-2-ene (about 3:1) were formed besides small amounts of 1-methylcyclohexa-1, 3-diene ( 9 ) and bicyclo [4.1.0]hept-3-ene ( 8 ). Under protic conditions (in ethylene-glycol) methylenecyclohex-3-ene, 1-methylcyclohexa-1, 3-diene and 1-methylcyclohexa-1, 4-diene ( 14 ) were produced in a ratio of 1:1:1. The direct mild thermolysis of cyclohex-3-ene-carbaldehyde p-toluenesulfonylhydrazone ( 1 ) in benzene solution afforded N-(p-toluenesulfinyl)-O-(p-toluenesulfinyl)-cyclohex-3-en-yl-α-methanolamine ( 15 ) and di-(cyclohex-3-en-yl-methyl)-ammonium p-toluenesulfonate ( 16 ), the structures of which were supported by their nmr. spectra and by alkaline cleavage.     

Pd‐Catalyzed Cycloisomerization of 4‐Aza‐1,6‐enynes to 3‐Aza‐bicyclo[4.1.0]hept‐2‐enes

A method for the synthesis of bicyclo[4.1.0]heptenes from 1,6‐enynes through Pd‐catalyzed cycloisomerization has been developed. N‐ and O‐tethered 1,6‐enynes were successfully transformed to their corresponding 3‐aza‐ and 3‐oxabicyclo[4.1.0]heptenes in reasonable‐to‐high yields using the catalysts [PdCl₂(CH₃CN)₂]/P(OPh)₃ or [Pd(maleimidate)₂(PPh₃)₂] in toluene. The computational calculations using density functional theory indicate that [PdCl₂{P(OPh)₃}] in the oxidation state Pd^II acts as the active catalyst species for the formation of 3‐azabicyclo[4.1.0]heptenes through 6‐endo‐dig cyclization.     

Electronic and Steric Structure of Thermal Isomerization Products of 1-Methyltricyclo[4.1.0.02,7]heptane Radical Cation

Distributions of the positive charge and unpaired electron in stable conformers of the thermal isomerization products of 1-methyltricyclo[4.1.0.02,7]heptane radical cation, having bicyclo[3.1.1]heptane, bicyclo[4.1.0]heptane, bicyclo[3.2.0]hept-6-ene, and 1,3-cycloheptadiene skeletons, were estimated by the PM3 semiempirical method.     

Preparation of bicyclo[3.2.0]heptane-2-endo,7-endo-diols: 1,3-diols with a chiral rigid backbone

The easily available bicyclo[3.2.0]hept-3-en-6-ones (1a-f) have been converted into the corresponding bicyclo[3.2.0]heptane-2-endo,7-endo-diols (4a-f) in an efficient and stereoselective fashion. This preparation opens a route to a family of 1,3-diols with a chiral rigid backbone, potentially suitable as nonracemic precursors for bidentate ligands in asymmetric synthesis.     

Action des nucleophiles sur la tosyloxy-8 cis bicyclo(4.2.0)octanone-7 trans: Mise en evidence spectroscopique d'un derive bicyclo(4.1.0)heptanique a jonction de cycle trans

The structure of compounds obtained by reaction of LiAlH₄ and NaOMe on trans 8-tosyloxy bicyclo(4.2.0)oct-3-éne-7-one in different solvents is determined and their stereochemistry assigned. The major product for NaOCH₃ reaction arises from cleavage of the cyclobutanone ring; with hydride, two compounds are formed which exhibit respectively trans bicyclo(4.1.0)heptanic and cycloheptadienic structures. The mechanisms of formation of the products are discussed and the determinative effect of ring junction stereochemistry on reaction development is underlined.     

Bicyclo[3.1.0]hex-(1,5)-ene and bicyclo[4.1.0]hept-(1,6)-ene

The formation and trapping of bicyclo[3.1.0]hex-(1,5)-ene and bicyclo[4.1.0]hept-(1,6)-ene from the corresponding vicinal dibromides is described.     

PtCl2-mediated cycloisomerization of unsaturated propargylic carboxylates

The PtCl₂-mediated cycloisomerization of unsaturated propargylic carboxylates yields differently functionalized bicyclo[4.1.0]heptane enol esters from moderate to good yield, in a very diastereoselective manner. We have prepared and submitted to PtCl₂-catalyzed cycloisomerization a series of differently substituted hept-1-en-6-ynes with different O-acyl (acetyl, trichloroacetyl, 3,4,5-trimethoxybenzoyl, etc.) protecting groups at propargylic positions, investigating also the effect of the geometry at the double bond, as well as the effect of the number of substituents at the alkene moiety. As a result, we have found that the O-acetyl migrating group is the best one in terms of simplicity and chemical yields. In this reaction we have isolated mixtures of compounds formed by minor 1-acetoxy-allenes and major bicyclo[4.1.0]heptane derivatives. Major products are the result of a sequential process involving steps of cycloisomerization plus cyclopropanation, followed by acyl migration. The basic methanolysis (K₂CO₃, MeOH) of these intermediates gave mixtures of cis and trans-caran-2-ones. This two-step protocol (cycloisomerization plus basic methanolysis) for the syntheses of α,β-unsaturated cyclopropyl ketones constitutes a synthetic alternative to the usual unfriendly, intramolecular cyclopropanation of unsaturated α-diazocarbonyl derivatives. The formation of these bicyclo[4.1.0]heptane derivatives is a simple, but efficient entry into the skeleton of the ‘carane’ family of natural products.     

Epoxidation with O2 using PdClNO2(CH3CN)2 catalysts: reactivity of the C-Pd bond in the intermediate complex formed during oxidation of norbornene

The reactivity of di-p-chlorobis[3-(nitrosooxy)bicyclo[2.2.]] hept-2-yl-C,N]dipalladium II can be modified by added reagents. In presence of CuCl₂, the thermal decomposition leading to epoxynorbornane is completely suppressed and an unequivocal rearrangement of the norbornane framework is observed.     

Uses of adsorbed reagents in the synthesis of reactive molecules via elimination reactions

The synthesis of reactive molecules (in vacuo) using reagents adsorbed on inert surfaces to effect elimination reactions has been investigated. Potassium t-butoxide adsorbed on Chromosorb W can be used to generate methylenecyclopropene from 2-chloromethylenecyclopropane and 1-vinylcyclopropene from either 1,4-dichlorospiropentane or 1-chloro-2-vinylcyclopropane. Both compounds can be characterized at low temperature using NMR and IR spectroscopy. Methyllithium on glass helices has been used in the reductive elimination of halogen from vicinal cyclopropyl dihalides to yield cyclopropenes. β-Halocyclopropylsilanes can be converted in high yield to the corresponding cyclopropene using tetra-n-butylammonium fluoride deposited on glass helices. The fluoride route has been used to generate bicyclo[4.1.0]hept-(1,6)-ene and bicyclo[4.1.0]hept-(1,7)-ene in the gas phase under conditions which allow either spectroscopic characterization or trapping as Diels-Alder adducts.     

Reaction of vinylidenecyclopropanes with aromatic imines in the presence of Lewis acids

1-Methyl-2-(2-methylpropenylidene)-1-phenylcyclopropane, 7-(2-methylpropenylidene)bicyclo[4.1.0]heptane, and (Z)-9-(2-methylpropenylidene)bicyclo[6.1.0]non-4-ene react with N-benzylideneanilines in the presence of boron trifluoride-ether complex to give pyrrolidine derivatives. Reactions of 1-methyl-1-phenyl-2-diphenylvinylidenecyclopropane with N-benzylideneanilines in the presence of BF₃·Et₂O, Yb(OTf)₃, or Sc(OTf)₃ lead to the formation of substituted 1,2,3,4-tetrahydroquinolines. 7-Diphenylvinylidenebicyclo[4.1.0]heptane in the presence of BF₃·Et₂O undergoes isomerization into 5-phenyl-8,9,10,11-tetrahydro-7H-cyclohepta[a]naphthalene.     

Synthesis and Chemistry of Bicyclo[4.1.0]hept-1,6-ene

Bicyclo[4.1.0]hept-1,6-ene has been generated by elimination of 1-chloro-2-(trimethysilyl)bicyclo[4.1.0]heptane in the gas phase over solid fluoride at 25 degrees C. The cyclopropene dimerizes by a rapid ene reaction forming two diastereomeric cyclopropenes. In tetrahydrofuran or chloroform the ene dimers couple to form a single crystalline triene tetramer, whereas a mixture of tricyclohexane tetramers is formed when the neat dimers are allowed to warm to room temperature. Oxidation by dimethyldioxirane or dioxygen gives carbonyl products. Quantum mechanical calculations yielded an increase in strain of approximately 17 kcal/mol over that for 1,2-dimethylcyclopropene. The potential enegy barrier to flexing (folding) along the fused double bond of bicyclo[4.1.0]hept-1,6-ene is only approximately 1 kcal/mol at the highest level of theory investigated.     

Brief syntheses of (±)-methyl shikimate, (±)-methyl epishikimate and structural variants

Two brief syntheses of (±)-methyl shikimate are described in a strategy which offers potentially flexible access to a range of analogues. New intramolecular rearrangement reactions of epoxides derived from methyl 7-oxabicyclo[2.2.1]hept-3-ene 6-carboxylate and methyl bicyclo[2.2.1]hept-3-ene 6-carboxylate are described.     

Synthese,Kristallstrukturen und spektroskopische Untersuchungen von 3d-Übergangsmetall-Komplexen mit Bicyclo[2.2.1]hept-5-en-2-endo,3-cis-dicarbonsäure und N,N-Donorliganden

Synthesis, Crystal Structures and Spectroscopic Investigations of 3d-Transition Metal Complexes with Bicyclo[2.2.1]hept-5-ene-2-endo,3-cis-dicarboxylic Acid and N,N-Donor Ligands The synthesis of coordination compounds of the general type [MLdam(H₂O)₃] · 2.5 H₂O with M = Mn²⁺, Co²⁺, Ni²⁺; H₂L = bicyclo[2.2.1]hept-5-ene-2-endo,3-cis-dicarboxylic acid and dam = 2,2′-dipyridyl, 1,10-phenanthroline has been described. The complexes have been characterized by elementary analysis, infrared and electronic spectra and magnetic susceptibility measurements. The results of X-ray crystal structure analyses of [MnLdipy(H₂O)₃] · 2.5 H₂O ( 1 a ) and [CoLdipy(H₂O)₃] · 2,5 H₂O ( 1 b ) show, that both compounds crystallize isotypically and prove the octahedral coordination of the metal atoms. The dicarboxylate anion is coordinated to the central atom by an O atom of only one carboxylate group, the other one is in the ionic state. One O atom of each carboxylate group makes an intramolecular hydrogen bond with a water molecule of the coordination sphere. The other crystal water molecules form a network of H bonds one with another and with the complex molecules, thus stabilizing the crystal packing.     

Prostaglandin synthesis from a fulvene with the ω-side chain equivalent

The acid-catalyzed hydrolysis of the Diels-Alder adduct of 6-(2,2-ethylene-dioxyheptyl) fulvene with 2-chloroacrylonitrile gave 7-anti-(3-oxo-1-trans-octenyl)-2-chloro-2-cyanobicyclo[2.2.1]hept-5-ene, which is an intermediate of 12-epi-prostaglandine. On the other hand, the hydrolysis of 7-(3,3-ethylenedioxyoctylidene)bicyclo-[2.2.1]hept-5-en-2-one, obtained from the Diels-Alder adduct of the fulvene with 2-chloroacryloyl chloride, gave a mixture (3:2) of 7-anti- and 7-syn-(3-oxo-1-trans-octenyl)bicyclo[2.2.1]hept-5-en-2-one. The latter compound was oonverted into prostaglandin F_2α.     

Heavy-Atom Tunneling in Bicyclo[4.1.0]hepta-2,4,6-trienes

Heavy-atom tunneling limits the lifetime and observability of bicyclo[4.1.0]hepta-2,4,6-triene, a key intermediate in the rearrangement of phenylcarbene. Bicyclo[4.1.0]hepta-2,4,6-triene had been proposed as the primary intermediate of the rearrangement of phenylcarbene, but despite many efforts evaded its characterization even in cryogenic matrices. By introducing fluorine substituents into the ortho-positions of the phenyl ring of phenylcarbene, the highly strained cyclopropene 1,5-difluorobicyclo[4.1.0]hepta-2,4,6-triene becomes stable enough to be characterized in argon matrices. However, even at 3 K this cyclopropene is only metastable and rearranges via heavy-atom tunneling to the corresponding cycloheptatetraene. Calculations suggest that fluorination is necessary to slow down the tunneling rearrangement of the bicycloheptatriene. The parent bicycloheptatriene rapidly rearranges via heavy-atom tunneling and therefore cannot be detected under matrix isolation conditions.     

Stereoselective synthesis of new (+)-1-{(1R,3R,6S)-4,7,7-trimethylbicyclo[4.1.0]hept-4-en-3-yl}ethan-1-one derivatives

A procedure was developed for the stereoselective synthesis of aminated derivatives of (+)-1-{(1R,3R,6S)-4,7,7-trimethylbicyclo[4.1.0]hept-4-en-3-yl}ethan-1-one. The configuration of the side-chain chiral center in (+)-1-{(1R,3R,6S)-4,7,7-trimethylbicyclo[4.1.0]hept-4-en-3-yl}ethan-1-ol was determined by X-ray analysis. Diketene and Meldrum’s acid were proposed as initial compounds for the synthesis of, respectively, 3-oxobutanoic and malonic acid esters having a 1-ethyl-4,7,7-trimethylbicyclo[4.1.0]hept-4-ene fragment.