Synthesis of Bridged Bicyclic Molecules using Halocarbenes. Derivatives of bicyclo[4.2.1]nonane

The addition of dichlorocarbene (generated by the interaction of sodium methoxide and ethyl trichloroacetate) to bicyclo[3.2.1]oct-2-ene, its 3-chloro and exo-3,4-dichloro derivatives gives the exo 1 : 1 adducts in yields of 94, 89 and 48%. By suitable chemical reactions of these adducts, convenient syntheses of bicyclo[4.2.1]nona-2,4-diene and bicyclo[4.2.1]non-3-ene, together with their monochloro, dichloro and trichloro derivatives are obtained. Bicyclo[4.2.1]-nonan-3-one is also obtained from bicyclo[4.2.1]non-3-ene in a synthesis starting from the readily available 5-hydroxymethylnorborn-2-ene in an overall yield of 20%.     

Heterohomoconjugation versus heterobicycloconjugation in 9-thiabicyclo[4.2.1]nona-2,4,7-triene

The bridged heterocycles, 9-thiabicyclo[4.2.1]nonane (3), 9-thiabicyclo[4.2.1]non-7-ene (4), 9-thiabicyclo[4.2.1]nona-2,4-diene (5) and 9-thiabicyclo[4.2.1]nona-2,4,7-triene (2), were examined by photoelectron spectroscopy and the various MO levels theoretically located in each case by CNDO/S calculation. The combined information is best interpretable in terms of localized π interaction between sulfur and ethylene but not butadiene. The conclusion therefore is that thiabicyclotriene 2 is not a heterobicycloconjugated molecule but rather one best described as heterohomoconjugated.     

Synthesis of anti-9-Bromo- and anti-9-Chlorobicyclo[4.2.1]nonatriene via Bicyclo[4.2.1]nonatriene→Bicyclo[4.2.1]nonatriene Rearrangement

The first syntheses of 9-bromo- and 9-chlorobicyclo[4.2.1]nona-2,4,6-trienes were each achieved in three stereoselective steps from the 9,9-bis(selenophenyl) derivative 9 in 79% overall yield for the bromide and 64% for the chloride. A deuterium-labeling experiment reveals the first rearrangement of a bicyclo[4.2.1]nonatriene which leaves the ring system intact.     

A study of the reaction of bicyclo[5.1.0]octa-2,5-diene with sulphur dioxide

Thermally-induced reaction between bicyclo[5.1.0]octa-2,5-diene (I) and sulphur dioxide under dry conditions is toluene-d₈ as solvent leads to the unexpected formation of the hitherto unknown diene sulphone 7-thiabicyclo[4.2.1]nona-2,4-diene 7,7-dioxide (II).     

Die isomeren bicyclo[4.2.1]nonen-(3)-ole-(2)und bicyclo[4.2.1]-nonanole-(2)1

The preparation of exo and endo bicyclo[4.2.1]nonen-(3)-ol-(2) (3) and (4), and the preparation of exo and endo bicyclo[4.2.1]nonanol-(2) (1) and (2) from 3,3-dihalotricyclo[4.2.1.0^2,4]nonyl derivatives is described. On the basis of the configuration of the allylic alkohols 3 and 4 the configuration of the saturated compounds 1 and 2 has been unequivocally determined.     

Die isomeren bicyclo[4.2.1]nonen-(2)-ole-(4) und bicyclo[4.2.1]nonanole-(3)1

The preparation of exo and endo bicyclo[4.2.1]nonen-(2)-ol-(4) (3) and (4), and the preparation of exo and endo bicyclo[4.2.1]nonanol-(3) (1) and (2) from 3,3-dihalotricyclo[4.2.1.0^2,4]nonenyl derivatives is described. On the basis of the configuration of the allylic alkohols 3 and 4 the configuration of the saturated compounds 1 and 2 has been unequivocally determined.     

Synthesis of N-ethoxycarbonyl-7-azabicyclo[4.2.1]nonane and N-ethoxycarbonyl-9-azabicyclo[4.2.1]nonane

The synthesis of N-ethoxycarbonyl-7-azabicyclo[4.2.1]nonane and N-ethoxycarbonyl-9-azabicyclo[4.2.1]nonane, starting from bicyclo[5.1.0]octan-2-one, is described. The key step is the cyclopropyl ring fission by pyridinium chloride.     

Valence isomerization of C9H10hydrocarbons: Photochemical reactions of bicyclo [3.2.2] nona-2,6,8-triene and its dihydro-derivatives

The valence isomerization reaction of bicyclo[3.2.2]nona-2,6,8-triene ($\text{2}$), which photoisomerized to two homologues of semibullvalene, was discussed with the photoreactions of its dihydro-dreivatives, bicyclo[3.2.2]nona-6,8-diene ($\text{3}$) and bicyclo[3.2.2]nona-2,6-diene ($\text{4}$).     

Herstellung der reinen,bicyclischen Olefine Bicyclo[4.2.1]non-2-en,Bicyclo[4.2.1]non-3-en und Bicyclo[4.2.1]non-7-en

Synthesis of the pure, bicyclic olefines Bicyclo[4.2.1]non-2-ene, Bicyclo[4.2.1]non-3-ene and Bicyclo[4.2.1]non-7-ene The synthesis of the olefines bicyclo[4.2.1]non-2-ene ( 3 ), bicyclo[4.2.1]non-3-ene ( 4 ) and bicyclo[4.2.1]non-7-ene ( 5 ) of high ‘certified’ purity from one common precursor ( 7 ) is described.     

The dominant role of hyperconjugation in the 9-oxabicyclo[4.2.1] nona-2,4,7-triene series

The synthesis and photodimerization of 9-oxabicyclo[4.2.1]nona-2,4,7-triene are described. The electronic structure of 9-oxabicyclo[4.2.1]nona-2,4,7-triene and variously saturated derivatives thereof was examined by means of UV photoelectron spectroscopy and calculation. The combined results give no indication of specific through-space lone-pair/τ or τ/τ interaction between the various appendages but offer clear sign of hyperconjugative coupling.     

Functionalized Cycloheptanes from Bicyclo[4.2.1]nonanes

Several oxidative, reductive and C,C-cleavage reactions were performed starting from the three bicyclo[4.2.1]nona-3,7-diene-2-one derivatives 1, 5 and 18 . The oxidations were selective and led to the diols 2,8 and 9 , and the epoxides 6,9 , and 20 . The reductions were selective only in the case of 20 21 ; otherwise they led to mixtures of the alcohols 10 and 11 , and of the dienes 14 and 15 . The periodate ring cleavages afforded the functionalized cycloheptane derivatives 3, 12, 13 and 16 . Configurational assignments were made on the basis of detailed ¹H-NMR and X-ray analysis of 20 .     

A homo Diels-Alder approach to bicyclo[4.2.1]nonanes

[reaction: see text] A new, high-yielding route to functionalized bicyclo[4.2.1]nonanes has been achieved utilizing homo Diels-Alder chemistry with subsequent Zeise's dimer-catalyzed opening of the cycloadduct.     

C2-Symmetric bicyclo[3.3.1]nona-2,6-diene and bicyclo[3.3.2]deca-2,6-diene: new chiral diene ligands based on the 1,5-cyclooctadiene framework

As a new type of C₂-symmetric chiral diene ligands, which coordinate to a metal by their 1,5-cyclooctadiene framework, we prepared 2,6-disubstituted bicyclo[3.3.1]nona-2,6-diene (bnd*) and bicyclo[3.3.2]deca-2,6-diene (bdd*), and examined their catalytic activity and enantioselectivity for rhodium-catalyzed asymmetric 1,4-addition to α,β-unsaturated ketones and 1,2-addition to N-sulfonylimines. High enantioselectivity of the Ph-bnd* ligand was observed in the addition of phenylboroxine to N-tosylimine and N-4-nitrobenzenesulfonylimine of 4-chlorobenzaldehyde to give phenyl(4-chlorophenyl)methylamines in high enantiomeric excess (98–99% ee).     

A Remarkable Synthesis of the Bicyclo[4.2.1]Nonenedione System

Allylation of the C-2 enolate of the bicyclo[3.3.1]nonenedione 1 proceeds with an unusual acyl migration to yield the C-allyl ester 5 of the rearranged bicyclo[4.2.1]nonenedione system.     

Interplay of orbital symmetry and nonstatistical dynamics in the thermal rearrangements of bicyclo[n.1.0]polyenes.

CASSCF and CASPT2 calculations have been carried out on some of the thermal rearrangements of bicyclo[2.1.0]pentene (BCP), bicyclo[4.1.0]hepta-2,4-diene (BCH), bicyclo[6.1.0]nona-2,4,6-triene (BCN), and 9,9-dicyanobicyclo[6.1.0]nona-2,4,6-triene (DCBCN). In addition, experiments have been conducted to determine the stereoselectivity and temperature dependence of the nondegenerate rearrangement of 9,9-dicyanobicyclo[6.1.0]nona-2,4,6-triene-exo-15N. The calculations and experiments allow a consistent picture to be drawn for these reactions. The principal conclusions are as follows. (1) The ring-walk rearrangements of BCP, BCN, and DCBCN are pericyclic reactions occurring with a strong preference for inversion of configuration at the migrating carbon. However, the ring-walk rearrangement of BCH is a nonpericyclic reaction. (2) The rearrangement of DCBCN to 9,9-dicyanobicyclo[4.2.1]nona-2,4,7-triene occurs with a preferred stereochemistry corresponding to a 1,3 migration with retention. However, this reaction is not a pericyclic process; the stereoselectivity is probably of dynamic origin. (3) Cyano substituents can significantly reduce the activation energy for a reaction occurring via a singlet biradical, but they do not necessarily cause the intermediate to sit in a deeper local minimum on the potential energy surface.     

[6π+2π]-Cycloaddition of α,ω-Diallenes and α,ω-Diacetylenes to 1,3,5-Cycloheptatriene in the Presence of TiCl4-Et2AlCl

[6π+2π]-Cycloaddition of α,ω-diallenes and α,ω-bis(trimethylsilyl)diacetylenes to 1,3,5-cycloheptatriene in the presence of a two-component catalytic system TiCl₄-Et₂AlCl was performed that led to the formation of bis(endo-bicyclo[4.2.1]nona-2,4-dienes) and bis(8-trimethylsilyl-endo-bicyclo[4.2.1]nona-2,4,7-trienes) linked by polymethylene spacer in 69–86% yields.     

Thermal [2+2] cycloaddition of allenynes: easy construction of bicyclo[6.2.0]deca-1,8-dienes, bicyclo[5.2.0]nona-1,7-dienes, and bicyclo[4.2.0]octa-1,6-dienes

The simple refluxing of allenynes, having a phenylsulfonyl functionality on the allenyl group, in xylene (or mesitylene) without microwave irradiation resulted in the efficient formation of bicyclo[5.2.0]nona-1,7-dienes and bicyclo[4.2.0]octa-1,6-dienes in high yields. This method was shown to be successfully applicable to the first construction of bicyclo[6.2.0]deca-1,8-dienes. Construction of the corresponding oxa- and azabicyclo[m.2.0] frameworks could also be attained. This thermal ring-closing reaction involves the formal [2+2] cycloaddition in which the distal double bond of an allenyl moiety exclusively served as one of the pi-components regardless of the position of the phenysulfonyl functionality on the allenyl moiety.     

ESR spectrum of the radical anion of bicyclo[3.2.2]nona-3,6,8-triene-2-one

The radical anion of bicyclo[3.2.2]nona-3,6,8-triene-2-one has been characterised by ESR spectroscopy.     

Near Cancellation of Through Space and Through Bond Interaction in bicyclo[3.2.2]nona-6,8-diene

The photoelectron spectra of bicyclo[3.2.2]nonane and its five dehydrogenated analogues are reported. Analysis of the π-bands reveals that the unsymmetrical diene 5 retains the ‘natural order’ of the π-orbitals present in the lower homologues, i. e. the in-phase below the out-of-phase combination of the basis π-orbitals π_a and π_c. The isomeric diene 4 is the first member of the symmetrical homologous series (I), which inverts this order, so that a ₁(π) (in phase!) lies above b ₂(π) (out-of-phase!).     

Titanium-catalyzed [6π+2π]-cycloaddition of Si-containing alkynes to bis(1,3,5-cycloheptatriene-7-yl)alkanes

The reaction between Si-containing alkynes and bis(1,3,5-cycloheptatriene-7-yl)alkanes in the presence of the two-component catalyst Ti(acac)₂Cl₂-Et₂AlCl, led to the selective formation of mono- and bis-adducts – {9-[4-(2,4,6-cycloheptatrienyl)alkyl]-8-alkyl(phenyl)bicyclo[4.2.1]nona-2,4,7-triene-7-yl}(trimethyl)silanes and bis(7-trimethylsilyl-8-alkyl(phenyl)bicyclo[4.2.1]nona-2,4,7-triene-7-yl)alkanes in 78–86% yield. The structures of the obtained cycloadducts were confirmed by ¹H and ¹³C NMR spectroscopy.