Tricyclo hexanes

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. 

Eine Anzahl von Cyclopropen-Derivaten wurde zu Tricyclo [3.1.0.0 hexan-Ringsystemen photodimerisiert. Es gibt jedoch noch keine Information liber Cyclopropen selbst. 

Die Strukturen der Tricyclo [S.l.O.O. j-hexan-Derivate (5) und (6) wurden durch spektroskopische Daten bestatigt. Aus sterischen Griinden wird in beiden Addukten die trans-Konfiguration des Cyclopropan-Teils in Bezug auf den Vierring angenommen. 

Cyclopropene cyclodimerization would give the tricyclo[3.1.0.02-4]hexane skeleton but the high temperatures required for thermal dimerizations would preclude formation of these highly strained derivatives. However, metal-catalyzed cyelodimerizations take place under milder... 

This method constitutes a convenient synthesis of substituted tricyclo[2.2.0.02,6]hexane derivatives. It is surprising that the ring strain associated with these derivatives would permit their preparation at such high temperatures. A homologous reaction involves the intramolecular [2 + 2] cycloaddition of 2-vinylphenyl substituted cyclopropenes 5 which give benzotricy-clo[3.2,0.02,7]heptenes 6.74 This reaction also proceeds by sensitized photolysis but gives a more complex mixture. 

In a related synthetic study, the alcohol 16 was hydrogenated over 5% palladium on charcoal in hexane to provide sj/ -tricyclo[4.2.1.125]dec-3-en-8-ol (17) in 98% yield.44 As can be seen in the following scheme, the common bond of the two cyclobutane rings is again the most vulnerable towards catalytic hydrogenation conditions. 

Exercise 1.4. Verify the classification of the pairs of groups in tricyclo[3.1.0.02,4]hexane. 

Nonconjugated dienes and polyenes have triplet photochemistry which may be considered to arise from intramolecular interaction of one excited double bond with an isolated ground-state double bond. For example, the photocyclization of enrfo-dicyclopentadiene can be effected using acetone as a sensitizer.286 Other more flexible 1,5-dienes, when sensitized to triplet states, cross couple to yield bicyclo[2.1.1]-hexane structures. For instance, triplet mercury atoms convert both 1,5-hexadiene and 1,5-cyclooctadiene to such structures.267 Irradiation of the cyclooctadiene in the presence of cuprous chloride produces the tricyclo derivative in good yield266 but recent evidence again indicates that this latter reaction may proceed via free-radical intermediates.269... 

The ylide (3.7 g, 10 mmol, prepared by the general method) in dichloromethane (20 ml) was treated with cuprous chloride (15 mg) under nitrogen at 0°C. The reaction mixture was stirred for 10 min at 0°C and for 1 h at room temperature. After filtration and concentration, the residue was chromatographed on silica gel (hexanes-ethyl acetate, 9 1) to give l-carbomethoxy-2-oxo-tricyclo[3.3.0.02,8]-octane (1.6 g, 90%) as an oil. 

Gassman reported the photoaddition of nucleophiles to radical cations of highly strained aliphatic polycyclic molecules such as tricyclo[2.2.1.0 ]hexane and related compounds. The radical cation of bicyclo [1.1.0] butane is postulated as a key intermediate (Scheme 12) [45-46]. 

Fig. 2. Temperature dependent H-NMR spectrum (60 MHz, toluene-dg) of [s-cis-T/ -l,2,5,6-tetramethyl-3,4-bis(methylene)-tricyclo[3.1.0.0 ]hexane]zirconocene (51).

For these complexes, the rate of carbonylation increases rapidly with increasing tr-alkyl character. Thus, (5-cis-butadiene)ZrCp2 (5a) is carbony-lated 2.5 times faster than the zirconocene complex of 1,2,5,6-tetramethyl-3,4-bis(methylene)tricyclo[3.1.0.0 ] hexane (51) (ambient temperature and 1 bar CO pressure) taken as a standard. Introduction of methyl groups at the internal carbon centers C2/C3 of the diene chain increases the carbonylation rate by a factor of 5 with phenyl groups at these positions increasing the rate by a factor of 250 (Table VIII). The organometallic reaction products have yet to be isolated or completely identified. Ultimately, zirconium enolate complexes (20) are probably formed in these... 

Tricyclo 2.2.0.01>s hexan 2-Diazo-3-oxo-l,4,5,6-tetramethyl- E14b, 1135 (Hydrazon-Oxidation)... 

Cyclopropenes are prone to dimerize and catalytic as well as photochemical dimerizations leading to tricyclo [3.1.0.0 " ] hexane derivatives are reported. Vinylidenecyclopropanes undergo regioselective as well as stereoselective addition of thiophenol to give (l-(phenylthio)vinyl)cyclopropanes (equation 135) . a-... 

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