Tricyclo 3,2.1.0> * octane

XII. Tricyclic Systems Containing a Cyclobxttane Ring The only system of this kind which appears to have been investigated kinetically in detail is tricyclo[3,3,0,0 ]octane (Srinivasan and Levi, 1964). At temperatures in the range 327 to 366° C the isomerization is a homogeneous first-order reaction. The observed products were 4-vinyl-cyclohexene, butadiene and 1,5-cyclo-octadiene. However, from separate studies on the cyclo-octadiene, it is concluded that the tricyclo-octane first isomerizes to the cyclo-octadiene which then undergoes secondary reactions to yield the other observed products. The observed rate is then the rate of this primaiy reaction, viz. ... 

The photoisomerization of cyclobutanones to transient car-benes has been used as part of an interesting synthesis of muscarine (Pirrung and DeAmicis). Intramolecular oxetan formation has been used as part of novel syntheses of medium-ring ethers (1) and the tricyclo-octane (2) (Carless et al. Gleiter and Kissler). Cossy et al. have employed the photoreductive cycliza-... 

The remarkable tricyclo-octanes shown below have recently been synthesized (Avram et al., 1964). They both yield 1,5-cyclo-octadiene on pyrolysis at 150° C which suggests that the kinetic parameters for these isomerizations cannot be two dissimilar to those for the isomerization of bicyclo[2,2,0]hexane. 

Fig. 23.6 Four isomeric tricyclo-octane derivatives showing extremely pronounced effects of stereochemistry on chemical shift values (see Fig. 23.7).

The addition of thermally generated difluorocarbene to bicyclo[2,2,l]hepta-2,5-dienes has been found to give the homo-Diels-Alder product (103 R = H) in addition to the endo- and exo-tricyclo-octanes (104 R = H) and (105 R = It is thought that the homo-addition product results from concerted cheletropic reaction and, by... 

In further studies of the tricyclo-octane system (329), Sauers reports the transformation of (330) into (331) with lithium aluminium hydride, and reactions... 

Cory and Renneboog53 have devised an efficient bicycloannulation for the synthesis of tricyclo[3.2.1.02,7]octane-6-one (66) as shown in equation 63. The method involves three steps (1) the enolate undergoes an initial conjugate addition to phenyl vinyl sulfone, (2) the resulting sulfone-stabilized carbanion undergoes an intramolecular Michael addition to the enone, and (3) the resulting enolate displaces phenylsulfinyl moiety from the tricyclooctanone. The amount of HMPA (3 mol equivalents) is critical for effective cyclization of the enolate. 

Recently a reverse perturbation effect of a cyclopropyl group on facial selectivities was described in two bicyclic systems, bicyclo[2.2.2]octane 59 and norbomane (bicyclo[2.2.1]heptane) 60 [124]. Bicyclo[2.2.2]octene 59a, annulated with an exo-cyclopropyl group, i.e., exo-tricyclo[3.2.2.0 ]non-6-ene, and 7-methylenenor-bomane 60a, annulated with an exo-cyclopropyl group, i.e., 8-... 

The most widely exploited photochemical cycloadditions involve irradiation of dienes in which the two double bonds are fairly close and result in formation of polycyclic cage compounds. Some examples of alkene photocyclizations are given in Scheme 6.9. Entry 1 is a transannular cyclization. The preference for the observed product over tricyclo[4.2.0.02,5]octane does not seem to have been analyzed in detail. Entries 2, 3, and 4 involve photolysis in the presence of Cu03SCF3. Entries 5 and 6 are cases in which the double bonds are in close proximity and can cyclize to caged structures. 

Another option is the twofold Michael addition/SN-type sequence of which manifold versions have been published. Thus, Padwa s group reported on the di-astereoselective synthesis of bicydo[3.3.0]octenes [199], while in another approach by Hagiwara and coworkers various tricyclo[3.2.1.0]octane derivatives and similar bridged compounds have been constructed [200]. The group of Spitzner has also been engaged intensively in Michael/Michael/SN-type processes [201]. One such ex-... 

The addition of the 2-substituted 2-cyclopentenone in (4.57) to ethylene affords an intermediate which is converted to tricyclo[4.2.0.01,4]octane 469a). A similar broken window compound was also obtained by an intramolecular photocycloaddition of a 2-cyclopentenone (4.58)469b). 

Before the explanation of ladder poly silanes is started, ladder compounds of other Group 14 elements are briefly mentioned. Hydrocarbons with a ladder-shaped carbon framework are known as ladderanes. The study on ladderanes goes back to 1927, when bicyclo[2.2.0]hexane ([2]ladderane) was synthesized by the reduction of dy-l,4-dibromocyclohexane with sodium.19 Ladderanes so far reported are tricyclo[4.2.0.02,5]octane ([3]ladderane),20 tetracyclo[4.4.0.02,507,1°]decane21 ([4]ladderane), and a number of their derivatives (Fig. 3). 

The structures of [2]ladderane and [3]ladderane were determined by electron diffraction.22,23 Each cyclobutane ring of bicyclo[2.2.0]hexane has a folded structure with fold angle 11.5°, and the molecule has C2 symmetry.22 Anti- and yy/7-tricyclo[4.2.0.02,5]octanes also have folded cyclobutane rings with fold angles of 8.0 and 9.0°, respectively.23 MM2 calculations on... 

The thermolysis of ladderanes has been studied in detail (Scheme 1). On heating, bicyclo[2.2.0]hexane and its derivatives exhibit skeletal inversion and cleavage to 1,5-hexadiene derivatives.26 The thermolysis of anti- and yyft-tricyclo[4.2.0.02,5]octanes and their derivatives gives cis,cis- and cis, trans-1,5-cyclooctadienes, cis- and trans-1,2-divinylcy clobutanes, and 4-vinylcyclohexene as ring-opening products.27-29 Furthermore, syn-tricyclo-[4.2.0.02,5]octane isomerizes to aw//-tricyclo[4.2.0.02,5]octane.29c,d The thermodynamic parameters and the reaction mechanisms for these thermal reactions have been discussed. 

The thermal isomerization of syn-2 has been studied in detail.68 When a solution of syn-2 in decahydronaphthalene was heated at 220 °C, it isomerized to anti-2 quantitatively (Scheme 15). When anti-2 in decahydronaphthalene was likewise heated at 220 °C, no isomerization of anti-2 to syn-2 was observed, and anti-2 was recovered. The thermolysis pathway is partially dilferent from that of the corresponding ladderane syn-tricyclo[4.2.0.02,5]octane was reported to give 1,5-cyclooctadienes, anti-tricyclo[4.2.0.02,5]octane, and 1,2-divinylcyclobutanes in 51, 41, and 8% yields, respectively.29c,d... 

The addition of halomethanes across the central bond of [l.l.l]propellane 78 leads to l-halo-7-(n-halomethyl)tricyclo[4.2.0.02,7]octanes 79, which are suitable precursors for the generation of type 80 carbenes.26... 

Trichloroacetyl fluoride, 45, 6 2-(Trichloromethyl)bicyclo[3.3.0]octane, from reaction of chloroform and cib,o i-l,5-cyclooctadiene, 47,10 hydrolysis with phosphoric acid to c.ro-m-bicyclo[3.3.0]octane-2-carboxylic acid, 47, 11 1,1,3-Trichloro- -nonane, 46,104 Tricyclo[2.2.1,02 6]heptan-3-ol, 46,... 

A detailed comparison of the rearrangement of 1,3-radicai cations and carbocations derived from tricyclo [3.3.0.0 " ] octanes has shown (by eiectron-transfer oxidation and protonation, respectiveiy) that electronic substituent effects on the diyi sites profoundly influence the regioseiectivities of the Wagner-Meerwein 1,2-shifts. The... 

MIRC and MIMIRC Reactions Leading to Spiropentanes, Tricyclo[3.2.1.0 ]octanes and Other Tricyclic Skeletons... 

The Michael addition followed by Intramolecular Ring Closure (MIRC) reactions have been recognized as a general synthetic approach to carbocyclic three-membered ring derivatives [1]. The enhanced Michael reactivity of methyl 2-chloro-2-cyclopropylideneacetate (1-Me) towards thiolates, alkoxides, lithiated amides and cyclohexadienolates (see below) allows one to perform highly efficient assemblies of spiropentane, tricyclo [3.2.1.0 ]octane, bicyclo [2.2.2] octane... 

The Cj - and 54-symmetric tetraesters of tricyclo[3.3.0.0 ]octane (430 and 431) have been prepared by oxidation of diene 429 To access the parent hydrocarbon (435), acid chloride 432 was transformed to the derived ketene which undergoes intramolecular [2+2] cycloaddition The resulting cyclobutanone (433) serves as precursor to perester 434 whose thermal decomposition proceeds with chain transfer in competition with cleavage The unique arrangement of the carbon atoms in 435 is such that the smallest rings are all five-membered. The highly symmetric structure may be viewed as a constrained cisoid bicyclo[3.3.0]octane (as well as the symbol of NATO). 

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