Cross-coupling of highly pyramidalized alkenes: A straightforward access to functionalized tetrasecododecahedradienes

The synthesis and chemical trapping of a highly pyramidalized pentacyclo[6.4.0.0(2,10).0(3,7).0(4,9)]dodec-8-ene containing ketal functions is reported. Its cross-coupling reaction with 3, 7-dimethyltricyclo[3.3.0.0(3,7)]oct-1(5)-ene followed by a [2 + 2] retrocycloaddition reaction gives a straightforward access to functionalized tetrasecododecahedradienes.     

Diels-Alder reactions of highly pyramidalized tricyclo[3.3.0.0]oct-1(5)-ene derivatives: further chemistry of pentacyclo[6.4.0.0.0.0]dodeca-5,8,11-triene

A study of the trapping of highly pyramidalized tricyclo[3.3.0.0^3,7]oct-1(5)-ene derivatives (generated from a 1,2-diiodo precursor on reaction with t-BuLi, 0.45% sodium amalgam and molten sodium) with different dienes (11,12-dimethylene-9,10-dihydro-9,10-ethanoanthracene, 1,3-diphenylisobenzofuran, 2,5-dimethylfuran and furan) is presented. Byproducts from the trapping of pentacyclo[6.4.0.0^2,10.0^3,7.0^4,9]dodeca-5,8,11-triene with 1,3-diphenylisobenzofuran have been synthesized and fully characterized, including an X-ray diffraction analysis. Also, the above triene has been cross coupled with 3,7-dimethyltricyclo[3.3.0.0^3,7]oct-1(5)ene to give a tetrasecododecahedratetraene derivative.     

Evidence for the formation of the (Ph3P)2Pt complex of 3,7-dimethyltricyclo[3.3.0.03,7]oct-1(5)-ene, the most highly pyramidalized alkene in a homologous series. Isolation and X-ray structure of the product of the ethanol addition to the complex

[reaction: see text] Attempts to isolate the (Ph(3)P)(2)Pt complex of the highly pyramidalized olefin 3,7-dimethyltricyclo[3.3.0.0(3,7)]oct-1(5)-ene 2 by generation of 2 in the presence of (Ph(3)P)(2)PtC(2)H(4), followed by crystallization of the complex (2-Pt) from THF-ethanol, resulted in the isolation of the adduct of 2-Pt with ethanol (5). Calculations confirm that addition of alcohol across the C1-C5 bond is more favorable in 2-Pt than in the corresponding (Ph(3)P)(2)Pt complexes of less pyramidalized olefins, despite the stronger Pt-C bonds in 2-Pt.     

Generation and trapping of tricyclo[3.3.0.0]oct-1(5)-ene derivatives containing carbonyl functionalities

Two new functionalized highly pyramidalized tricyclo[3.3.0.0^3,7]oct-1(5)-ene derivatives containing carbonyl functionalities have been trapped as Diels-Alder adducts, although they failed to dimerize. An interesting fragmentation of the bisnoradamantane skeleton to norbornane derivatives has also been observed.     

Generation and reactions of new ether and acetal functionalized tricyclo[3.3.0.0]oct-1(5)-ene derivatives. DSC and NMR studies on the [2+2] retrocycloaddition of several cyclobutane dimers

Two new highly pyramidalized tricyclo[3.3.0.0^3,7]oct-1(5)-ene derivatives containing ether and acetal functionalities have been generated, trapped as Diels-Alder adducts and dimerized. The initially obtained diene dimers were photochemically converted into cyclobutane derivatives. The thermal reversion of several cyclobutane derivatives to the corresponding dienes has been studied by ¹H NMR, ab initio calculations and DSC. For the first time, transannular additions of bromine and iodine to a diene dimer of this series have been observed.     

Polyfunctionalized cage compounds by pericyclic domino processes of 4,5-dicyanopyridazine with dienes: applications and limits

The title compound 1 was found to behave as an attractive masked bis-diene to give 4-oxatricyclo[4.3.1.0(3,7)]dec-8-ene, 5-aza- and 5-silatricyclo[5.3.1.0(3,8)]undec-9-ene, tricyclo[3.2.1.0(2, 7)]oct-3-ene, and tricyclo[5.3.1.0(3,8)]undec-9-ene derivatives through purely pericyclic, three-step homodomino processes with diverse bis-dienophiles; whereas the reaction with myrcene (21) was characterized by a complete sitoselectivity affording compound 25, treatment of 1 with (R)-(-)-beta-citronellene (26a) gave a 3:1 mixture of the homochiral diastereomers 30a and 31a. Some limits of this methodology, mainly arising from competitive side reactions upon the key cyclohexa-1,3-diene intermediates, are emphasized. The structures of the new compounds were established on the basis of spectral data.     

Dehalogenation of 1,3-diiodotricyclo[3.3.0.0(3,7)]octane: generation of 1,3-dehydrotricyclo[3.3.0.0(3,7)]octane, a 2,5-methano-bridged [2.2.1]propellane

Compounds isolated from the reaction of (+/-)-1,3-diiodotricyclo[3.3.0.0(3,7)]octane with molten sodium or tBuLi suggest the intermediate formation of (+/-)-1,3-dehydrotricyclo[3.3.0.0(3,7)]octane. Worthy of note is the formation of stereoisomeric bi(5-methylenebicyclo[2.2.1]hept-2-ylidene) derivatives, probably by coupling of two units of (+/-)-1,3-dehydrotricyclo[3.3.0.0(3,7)]octane of the same or different absolute configuration followed by fragmentation, processes that have been studied by theoretical calculations.     

Role of singlet diradicals in reactions of 2-carbenabicyclo[3.2.1]octa-3,6-diene

The generation of 2-carbenabicyclo[3.2.1]octa-3,6-diene (1) results in the formation of C(8)H(8) hydrocarbons endo-6-ethynylbicyclo[3.1.0]hex-2-ene (4), semibullvalene (5), and 5-ethynyl-1,3-cyclohexadiene (6), and C(8)H(10) hydrocarbons bicyclo[3.2.1]octa-2,6-diene (7), tricyclo[3.2.1.0(4,6)]oct-2-ene (8), and tetracyclo[3.3.0.0(2,8)0(4,6)]octane (9). Focus is placed on three mechanistic pathways for the formation of the C(8)H(10) hydrocarbon fraction: (a) abstraction of hydrogen by triplet carbene 1T to produce an equilibrating set of monoradicals, (b) interconversion of triplet carbene 1T into tricyclic triplet diradical 19T and tetracyclic triplet diradical 20T, and (c) interconversion of singlet 1S with analogous singlet diradical 19S and 20S. Ab initio calculations at the (U)B3LYP/6-311+G(3df,2p)//(U)B3LYP/6-31G(d,p) and broken spin symmetry UBS B3LYP/6-311+G(3df,2p)//B3LYP/6-31G(d,p) levels rule out choices (a) and (b) and are consistent with the singlet diradical process.     

Alternative syntheses of the new D2d symmetric tetramethyl tricyclo- [3.3.0.0(3,7)]octane-1,3,5,7-tetracarboxylate

Two alternative syntheses of the new D2d symmetric tetramethyl tricyclo[3.3.0.0(3,7)]octane-1,3,5,7-tetracarboxylate from the known dimethyl 3,7-dioxo-cis-bicyclo[3.3.0]octane-1,5-dicarboxylate and 1,5-(2,2'-biphenylene)-cis-bicyclo[3.3.0]octane-3,7-dione are described.     

The Reaction of Dihalocarbenes with Quadricyclane

The reactions of difluoro-, dichloro- and dibromocarbene with quadricyclane ( 2 ) were examined. In all cases, conversions were low (4–15%), but three distinct reaction courses were observed: cleavage, 1,2-addition, and 1,4-addition. Difluorocarbene gave mainly 6-endo-(2,2-difluorovinyl)-cis-bicyclo[3.1.0]hex-2-ene ( 8 ; 52–89% relative yield), together with minor amounts of exo-3,3-difluorotricyclo[3.2.1.0^2,4]oct-6-ene (7; 13–17%), and 4,4-difluorotetracyclo[3.3.0.0^2,8.0^3,6]octane ( 5 ; 2–4%). Dichlorocarbene gave analogous products, but in relative yields of 35 ( 17 ), 51 ( 11 ), and 12% ( 16 ). The product 11 of 1,2-endo addition underwent further rearrangement to its allylic derivative 12 . A small amount of 1,2-endo addition also occurred (2% of 14 / 15 ). Dibromocarbene gave predominantly products derived from rearrangement of the 1,2-exo (61% of 20 / 21 ) and 1,2-endo adducts (10% of 23 / 24 ). In addition, a significant amount of 4,4-dibromotetracyclo[3.3.0.0^2,8.0^3,6]octane ( 25 ; 21%) was formed. The cleavage product, 6-endo-(2,2-dibromovinyl)-cis-bicyclo[3.1.0]hex-2-ene ( 26 ) was also observed (7%). The yields and product compositions were compared to those obtained from norbornadiene ( 1 ) and found to be entirely different (Table 1), for example no cleavage occurred with difluorocarbene.     

Synthesis and reactivity of trans-Tricyclo

The first synthesis of trans-tricyclo[4.2.0.0(1,3)]oct-4-ene (1), an ethenyl bridged spirohexane, was accomplished in four steps starting from Carpino et al. gem-dichloro ketone 6. An X-ray crystal structure of 1 with one substituent was obtained to provide geometry data on this novel ring system and to confirm the stereochemical assignment of the penultimate synthetic intermediate. Tricyclo[4.2.0. 0(1,3)]oct-4-ene is surprisingly stable. It reacts with glacial acetic acid but only slowly at 145 degrees C; the products were isolated and identified. A unimolecular rearrangement takes place at elevated temperatures (165 degrees C and higher), presumably, via a biradical intermediate to afford tricyclo[4.2.0.0(1,5)]oct-3-ene (23). The structure of this 1,5-bridged bicyclo[2.1.0]pentane derivative was established by NMR and an X-ray crystal structure of its Diels-Alder adduct with isobenzofuran. Tricyclo[4.2.0.0(1, 3)]oct-4-ene equilibrates with 23, so equilibrium constants and reaction rates were measured over a 20 degrees C temperature range from 180 degrees C to 200 degrees C. The difference in the heats of formation (DeltaDeltaH degrees (f) (23 - 1)) is -2.1 kcal/mol, which is in good agreement with ab initio (HF and MP2) calculations using the 6-31G(d) basis set (-1.9 (HF) and -1.4 (MP2) kcal/mol). Computations on trans-tricyclo[4.2.0.0(1,3)]octane and spirohexane also were carried out, and the structures and energies were compared.     

Phosphabenzenes as monodentate pi-acceptor ligands for rhodium-catalyzed hydroformylation

A new class of phosphinine/rhodium catalysts for the hydroformylation of terminal and internal alkenes is presented in this study. A series of phosphabenzenes 1-14 has been prepared by condensation of phosphane or tris(trimethylsilyl)phosphane with the corresponding pyrylium salt. Trans-[(phosphabenzene)2RhCl(CO)] complexes 21-25 have been prepared and studied spectroscopically and by X-ray crystal-structure analysis. The hydroformylation of oct-1-ene has been used to identify optimal catalyst preformation and reaction conditions. Hydroformylation studies with 15 monophosphabenzenes have been performed. The catalytic performance is dominated by steric influences, with the phosphabenzene 8/rhodium system being the most active catalyst. Turnover frequencies of up to 45370 h(-1) for the hydroformylation of oct-1-ene have been determined. In further studies, hydroformylation activity toward more highly substituted alkenes was investigated and compared with the standard industrial triphenylphosphane/rhodium catalyst. The reactivity differences between the phosphabenzene and the triphenylphosphane catalyst increase on going to the more highly substituted alkenes. Even tetrasubstituted alkenes reacted with the phosphabenzene catalyst, whereas the triphenylphosphane system failed to give any product. In situ pressure NMR experiments have been performed to identify the resting state of the catalyst. A monophosphabenzene complex [(phosphinine 8)Ir(CO)3H] could be detected as the predominant catalyst resting state.     

The Synthesis and Chemistry of 8-Substituted Bicyclo[5.1.0]oct-1(8)-ene

8-Bromobicyclo[5.1.0]oct-1(8)-cne (7), an intermediate for the preparation of 8-substituted bicyclo[5.1.0]oct-1(8)-enes, was synthesized by denomination of 1,8,8-tribromobicyclo[5.1.0]octane (6). Compound 7 underwent bromo-lithium exchange followed by nucleophilic substitution reactions to generate bicyclo[5.1.0]oct-1(8)-ene (5), 8-methylbicyclo[5.1.0]oct-1(8)-ene (10), and 8-trimethylsilylbicyclo[5.1.0]oct-1(8)-ene (11). The bicyclic cyclopropenes 7, 5, 10, and 11 reacted with cyclopentadiene to form adducts 12, 13, 14, and 15, respectively. All of these Diels-Alder adducts are endo-exo isomers (endo-addition from the view of the cyclopropene and exo-addition from the view of the cyclooctene).     

Generation and reactions of Pentacyclo[4.3.0.0(2,4).0(3,8).0(5,7)]non-4-ene

The highly pyramidalized alkene, pentacyclo[4.3.0.0(2,4).0(3,8).0(5,7)]non-4-ene (9), has been generated via treatment of 4,5-diiodopentacyclo[4.3.0.0(2,4).0(3,8).0(5,7)]nonane (12) with n-butyllithium and tert-butyllithium. The title alkene has also been trapped as its Diels-Alder adduct with 1,3-diphenylisobenzofuran, 2,5-dimethylfuran, and spiro[2.4]hepta-4,6-diene. Products resulting from alkyllithium addition to the pyramidalized double bond of 9 have been isolated and fully characterized spectroscopically. The geometry, olefin strain energy, heat of hydrogenation, and relative HOMO/LUMO energies of 9 have been obtained by ab initio calculations at the MP2 and B3LYP levels using the 6-31G* basis set.     

Zirconium-catalyzed reaction of terminal alkenes with triethylindium

Terminal alkenes (undec-1-ene, oct-1-ene, and allylbenzene) reacted with triethylindium in the presence of a catalytic amount of Cp₂ZrCl₂ in hexane to give mixtures of three organoindium compounds whose hydrolysis in D₂O afforded 2-substituted 1,4-dideuterobutane containing minor amounts of 2-substituted 1- and 4-deuterobutanes.     

One-step synthesis of epoxy(perfluoroalkyl)alkenes

Epoxy(perfluoroalkyl)alkenes were synthesized in one step by reaction of perfluoroalkyl iodides with 2-(allyloxymethyl)oxirane and 2-(oct-7-en-1-yl)oxirane in the presence of sodium dithionite and 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) under mild conditions.     

Palladium-catalyzed [2 + 2 + 2] cocyclotrimerization of benzynes with bicyclic alkenes: an efficient route to anellated 9,10-dihydrophenanthrene derivatives and polyaromatic compounds

An efficient method for the cocyclotrimerization of bicyclic alkenes and benzynes catalyzed by palladium phosphine complexes to give the corresponding norbornane anellated 9,10-dihydrophenanthrene derivatives is described. Bicyclic alkenes 1a-i undergo [2 + 2 + 2] cocyclotrimerization with benzynes generated from precursors 2a-d [2-(trimethylsilyl)phenyl triflate (2a), 4,5-dimethyl-2-(trimethylsilyl)phenyl triflate (2b), 6-(trimethylsilyl)-2,3-dihydro-1H-5-indenyl triflate (2c), 4-methyl-2-(trimethylsilyl)phenyl triflate (2d)] in the presence of PdCl(2)(PPh(3))(2) in acetonitrile at ambient temperature to yield anellated 9,10-dihydrophenanthrene products 3a-r in moderate to excellent yields. The [2 + 2 + 2] cocyclotrimerization products from oxa- and azabicyclic alkenes can be applied for the synthesis of polyaromatics, substituted benzo[b]triphenylenes (8a-f), via a simple Lewis acid mediated deoxyaromatization in good yields. In addition the [2 + 2 + 2] products undergo retro Diels-Alder reaction readily, providing a new method for the synthesis of substituted phenanthrenes and for generating isobenzofurans. A plausible mechanism is proposed to account for the catalytic [2 + 2 + 2] cycloaddition reaction.     

The Non-planarity of the Bicyclo[2.2.1]hept-2-ene Double bond. Crystal Structures of Bicyclo[2.2.2]oct-2-ene,Bicyclo[2.2.1]hept-2-ene,and Bicyclo[2.1.1]hex-2-ene Systems

The crystal structures of (1R,4R,5S,8S)-9,10-dimethylidentricyclo[6.2.1.0^2,7]undec2(7)-ene-4,5-dicarboxylic anhydride ( 3 ), (1R,4R,5S,8S)11-isopropylidene-9,10-dimethylidenetricyclo[6.2.1.m^2,7]undec-2(7)-ene-4,5-dicarboxylic anhydride ( 6 ), (1R,4R,5S8S)-9,10-dimethylidenetricyclo[6.2.2.0^2,7]dodec-2(7)-ene-4,5-dicarboxylic anhydride ( 9 ), (1R4R5S8S)-TRICYCLO[6.2.2.0^2,7]dodeca-2(7), 9-diene-4,5-dicarboxylic anhydride ( 12 ) and (4R,5S)-tricyclo[6.1.1.0^2.7]dec-2(7)-ene-4,5-dicarboxylic acid ( 16 ) were established by X-ray diffraction. The alkyl substituents onto the endocyclic bicyclo[2.2.1]hept-2-ene double bond deviate from the C(1), C(2), C(3), C(4), plane by 13.5°4 in 3 and by 13.9° in 6 , leaning toward the endo-face. No such out-of-plane deformations were observed with the bicyclo[2.2.2]oct-2-ene derivatives 9 and 12 . The exocyclic s-cis-butadiene moieties in 3, 6 and 9 do not deviate significantly from planarity. The deviation from planarity of the double bond n bicyclo[2.2.1]hept-2-ene derivatives and planarity in bicyclo[2.2.2]oct-2-ene analogues is shown to be general by analysis of all known structures in the Cambridge Crystallographic Data File. The non-planarity of the bicyclo[2.2.1]hept-2-ene double bond cannot be attributed only to bond-angle deformations which would favour rehybridizatoin of the olefinic C-atoms since the double bond in the more strained bicyclo[2.1.1]hex-2-ene drivative 16 deviates from planarity by less than 4°.     

The predictable behaviour of cations deriving from endo-4-chlorotetracyclo[3.3.0.0.2,8O.3,6]octane.

Silver cation-initiated ionization of the title compound in aqueous dioxane gives the exo and endo-tetracyclo[3.3.0.0.^2,8O.^4,6]octane-3-ols (35 and 65%). Thermal isomerization in chloroform gives the exo and endo isomers of 4-chlorobicyclo[3.2.1]octa-2,6-dienes (3.5 and 1.5%) and 6-chlorotricyclo[3.2.1.0.^2,7]oct-3-ene (90 and 5%). The behaviour of the cations involved is compatible with MINDO/3 calculations.     

Photocycloaddition of ethylvinylether and cyclopentene to 3.5-dimethylanisole

Photocycloadition of ethylvinylether and cyclopentene to 3,5-dimethylanisole yields derivatives of 1-methoxy-2, 4-dimethyltricyclo [3.3.0.0^2,8]oct-3-ene in which the substituents at positions 6 and/or 7 are endo. Structural proofs are based on 250 MHz ¹H and 62.9 MHz ¹³C NMR spectra.