Tricyclo heptan

Further evidence for the pathways described above comes from labeling studies in which deuterium replaced both hydrogens at the bicyclobutane bridgehead positions, leading to the cyclic dienes with deuteriums at carbons 2 and 3 " This study also included an unsaturated derivative of the tricyclo heptane above as well as measurements of activation parameters for all of the bridged bicyclobutane systems known at that point of time. 

Zur Reduktion von 3-exo-Chlormercuri-5-exo-acetoxy-tricyclof2.2.1.02,6]heptan zui-exo-Acetoxy- undi-exo-Hydroxy-tricyclo[2.2.1.0i , Jieptan durch das Radikal-Anion des Naphthalins s.Bd. XIII/2b, S. 313 ... 

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-... 

Homoconjugation results in enhanced reactivity of substrates toward ionic hydrogenation. Bicyclo[2.2.1]hepta-2,5-diene forms a mixture of the trifluoroac-etate esters of bicyclo[2.2.1]hepten-2-ol, tricyclo[2.2.1.02 6]heptan-3-ol, and bicyclo[2.2.1]heptan-2-ol in a 62 20 17 ratio on treatment with 10 equivalents of triethylsilane and 20 equivalents of trifluoroacetic acid for 24 hours at room temperature (Eq. 96), 230... 

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,... 

Scheme 6.33 Liberation of tricyclo[4.1.0.02,7]hepta-3,4-diene (142) from 7,7-dibromotetracyclo[4.1.0.02,4.03,5]heptane (141) and formation of [2 + 2]-cycloadducts of 142.

Bicyclo[2.2.1]hept-2-enes react with p-bromostyrene to form 1 2 adducts 2-(phenylethynyl)-3-(2-phenylethenyl)bicyclo[2.2.1]heptane and the ring-closed tricyclo compound are both isolated (Scheme 6.32) [45]. Comparison of these results should be with those of the reaction in the absence of the quaternary ammonium salt, where the major reaction pathway leads to 2 1 and 1 1 adducts [46]. 

Thiocarbonyl tetrachloride, i6, 21 Thionyl chloride, 45, 16, 98 Thiophosgene, 45, 21 Thiophosphoryl chloride, reaction with methylmagnesium bromide to yield tetramethylbiphosphine disulfide, 45,102 Toluenesulfonybromide, 46, 88 Trichloroacetyl fluoride, 46, 6 1,1,3-Trichloiio- -nonane, 46,104 Tricyclo[2.2.1.0 ]heptan-3-ol, 45,... 

Methyl tricyclo[4.1.0.0 ]heptane-l-carboxylate gives a cation-radical in which the spin density is almost completely localized on C-1 while the positive charge is on C-7. The revealed structural feature of the intermediate cation-radical fairly explains the regioselectivity of N,N-dichlorobenzenesulfonamide addition to the molecular precursor of this cation-radical. In the reaction mentioned, the nucleophilic nitrogen atom of the reactant adds to electrophilic C-7, and the chlorine radical attacks C-1 whose spin population is maximal (Zverev and Vasin 1998, 2000). 

Actually, the earliest derivative of a vinylcyclopropane radical cation was a serendipitous discovery. It was formed by an unusual hydrogen shift upon photo-induced electron transfer oxidation of tricyclo[4.1.0.0 ]heptane (26). This result has been questioned on the grounds that the same rearrangement was not observed in a Freon matrix. However, there is no basis for the assumption that radical cation reactions in frozen matrices at cryogenic temperatures should follow the same course as those at room temperature in fluid solution and in the presence of a radical anion, which is potentially a strong base. In several cases, matrix reactions have taken a decidedly different course from those in solution. For example, radiolysis of 8 in a Freon matrix generated the bicyclo[3.2.0]hepta-2,6-diene radical cation (27 ), or caused retro-Diels-Alder cleavage yet, the... 

As can be seen, both routes lead to the same product. Nevertheless, in compounds where the conformational flexibility of the bicyclobutane frameworks is restricted, 1,3-addition is found to be favored via the diequatorial mode.12,13 This aspect is illustrated in a reaction in which iodine reacted with tricyclo[4.1.0.02,7]heptane in carbon tetrachloride to give 6,7-diiodobicy-clo[3.1. l]heptane (9) in 55% yield.13 In support of this stereochemistry, the majority of results obtained from the dculeration of tricyclo[4.1.0.02,7]heptane suggested that the attack is from the equatorial position.14 Theoretical studies also support the notion that the equatorial approach of an electrophile to the bridgehead of bicyclo[l.1.0Jbutane is thermodynamically favored.14,15... 

It has been suggested that tricyclo[4.1.0.02 7]heptanc should have a low energy cwt/ -bonding orbital which readily accepts an electron to form an anion radical. The high electron density of the central bond then directs the subsequent protonation-reduction-protonation to give bicyclo[3.1.1]heptane.17... 

In the absence of solvent, only syn stereoselectivity and not stereospecificity was observed for the nucleophilic addition of secondary amines such as dimethylamine, diethylamine, piperidine and morpholine to bicyclo[1.1.0]butane-l-carbonitrile. However, similar addition to 3-methylbicy-clo[l. 1.0]butane-l-carbonitrile was more stereoselective.22 However, the addition of sodium methancthiolate to 3-methylbicyclo[1.1.0]butane-l-carbonitrile, methyl bicyclo[l.l.0]butane-1-carboxylate, methyl 3-mcthylbicyclo[1.1.0]butane-l-carboxylate and methyl tricyclo[4.1.0.02 7]-heptane-l-carboxylate also afforded mixtures of cis- and p-rms-cyclobutancs in > 50% yield, with methyl bicyclo[1.1.0]butane-l-carboxylate showing greater anti stereoselectivity.23,24... 

For substituted tricyclo[4.1.0.02,7]heptanes, similar addition of benzenethiol in diethyl ether gave an isomeric mixture of bicyclo[3.1.1]heptanes.35 As shown in the mechanistic scheme, the 1,3-disubstituted patterns of the bicyclo[3.1, l]heptanes are governed by the regiospecific attack of the thiol radical on the sterieally less hindered bridgehead carbon. The results of these radical additions arc summarized for bicyclo[n.l.l]alkanes (Table 8)35 and bicyclo[1.1.0]butanes (Table 9). 

Other examples of the synthesis of cyclobutanes with abstraction of an allylic hydrogen are the photochemical formation of tricyclo[4.1.0.03,7]heptan-5-ones (e.g., 5) from norborn-5-en-2-ones33 and of bicyclo[4.2.0]octenes (e.g., 7) from doubly unsaturated ketones.34... 

Carbenes are known intermediates in the thermolytic or photolytic decomposition of the lithium or sodium salts of tosylhydrazones, which, for endocyclic carbenes, results in ring contraction when the elimination of / - or y-hydrogens is impeded. Simple cyclobutanes generally cannot be prepared by this route from monocyclic cyclopentanone tosylhydrazones. However, the lithium salt of bicyclo[2.2.1]heptan-7-one tosylhydrazone gave bicyclo[3.2.0]hept-l-ene (4) as the major product (74%) by vacuum pyrolysis at 185 JC/20 Torr, together with bicyclo[2.2.1]heptane (14%) and tricyclo[2.2.1.02,7]heptane (12%) in 80% overall yield.67... 

On the other hand, it has been reported that the bridgehead-substituted cyclobutane 3-chlorotet-racyclo[3.3.0.02,8.03 6]octan-4-one (11) was dehalogenated in good yield (82%) by sodium in tert-butyl alcohol if protected as the acetal 12.145 When 11 was not protected, ring opening to e c o-tricyclo[2.2.1.02 6]heptane-3-methanol resulted. 

By virtue of their high stereoselectivity, nucleophilic additions to cyclobutanone derivatives have been utilized to prepare the five-membered rings of prostaglandins with complete control of stereochemistry. This chemistry has been reviewed.65 The conversion of 3-emio-(tert-butyldimethylsiloxy)tricyclo[3.2.0.02,7]heptan-6-one (30) to 7-am7-(3-terf-butyldimethylsiloxy-oct-l-enyl)-5- ,wdy-( rt-butyldimethylsiloxy)bicyclo[2.2.1]heptan-2-one (31) in 88% yield provides a good example.66... 

Investigations into the solvolysis of a //-7-norbornenyl derivatives, and on the nature of the cationic intermediates involved,7 led to the conclusion that the bicyclo[2.2.1]hept-2-ene system is more stable than the tricyclo[4.1.0.03,7]heptane system.13,14 In terms of reactivity, the tricyclic derivatives surpass the bicyclic analogs by a large factor.15-17 For example, in 80% aqueous acetone containing dilute perchloric acid, 2-methoxytricyclo[4.1.0.03,7]heptane (3) is transformed quickly and quantitatively to u r/-bicyclo[2.2.1]hept-2-en-7-ol (4).18... 

Apart from the rearrangement of the tricyclo[4.1.0.03/7]heptane to the bicyclo[2.2.1]hept-2-ene system under acid catalysis, it can be effected by silver(I) perchlorate [silver(I) assisted ionization]19 and by photolysis at 185 nm.20... 

Likewise, 1,4-diazepine 5i-m,83 1,4-thiazepine 5h,83 1,4-oxazepine 5a-g,83 and 1,4-oxazepin-5-one92 derivatives were formed in good yield on thermolysis of suitably substituted dihetera-tricyclo[3.2.0.02,4]heptanes in refluxing toluene or xylene. 

The photoreactions of electron acceptors with several bridged bicyclobutane systems, e.g. tricyclo[4.1.0.02,7]heptane (75), give rise to CIDNP effects supporting negative hfcs for Ht and FI7 and positive hfcs for H2 and H6 as well as H3 3. and H5<5,. These results would place electron spin density at C, and C7, in agreement with the involvement of the A, HOMO (121) [249, 284],... 

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