Tricyclo 8- -: synthesis

The synthesis of adamantane (15), tricyclo[3.3.1.1 ]decane [281-23-2] by heating tetrahydrodicyclopentadiene (14) [6004-38-2] in the presence of aluminum trichloride illustrates another aspect of the synthetic utiHty of DCPD (80). Adamantane is the base for dmgs that control German measles and influenza (80-81) (see ANTIVIRAL AGENTS). 

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. 

CYCLOBUTADIENE IN SYNTHESIS endo-TRICYCLO[4.4.0.02 5]DECA-3,8-DIEN-7,IO-DIONE... 

The synthesis of fUido-tricyclo[4.4.0.02 5]deca-3,8-dien-7,10-dione and verification of its endo-configuration has been reported earlier.3 This adduet is a useful starting material for the syntheses of tetracyclo-[5.3.0.02 6.03 10]deca-4,8-diene,s tricyclo[4.4.0.02 5]deca-3,7,9-triene,6 cis, syn, cjs-tricyclo[5.3.0.02,6]deca-4,8-dien-3,10-dione,7 and 4-oxahexa-cyclo[5.4.0.02 6.03 10.05 9.08,11]undecane.a... 

The recent upsurge of interest in systems of theoretical interest demands practical syntheses of several important compounds. These are BICYCLO[2.l.0]PENT-2-ENE, BENZOCYCLOPROPENE, 1,6-OXIDO[10]ANNULENE, and others. ewdo-TRICYCLO[4.4.0.02 5]-DECA-3,8-DIENE-7,10-DIONE is utilized as a model for the use of CYCLOBUTADIENE IN SYNTHESIS, and a stable monomeric ketene, icri-BUTYLCYANOKETENE offers opportunities for further studies of this interesting species. 

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-... 

Barriault developed a new pericyclic domino process for the synthesis of the bioactive diterpenoid vinigrol (4-262), which was isolated from Vtrgaria nigra [92]. The natural product possesses antihypertensive and anti-platelet-aggregating properties. 4-262 contains a unique tricyclo [4.4.4.04a8a]tetradecane framework, which could be obtained by a combination of an oxy-Cope, a Claisen and an ene reaction... 

Photoelimination of nitrogen from 1-pyrazolines has also been employed in the synthesis of tricyclo[3.2.1.02,4]oct-6-ene,338 prismane,339 quadri-cyclane,340 snoutene ,341 and marasmic acid.342 The trimethylenemethanes 414 have been prepared by photolysis of azoalkanes 415 and characterized spectroscopically.343 Dimerization and cycloaddition to alkenes of these biradicals have been reported.344... 

The di-rc-methane rearrangement is also a convenient way of obtaining polycyclic fused ring systems as illustrated in the synthesis of a tricyclo-undecane (3.17) 327). In the irradiation of dihydrotriquinacene the initial bonding scheme is identical as in (3.14) but ultimate cyclopropane formation is hindered by structural reasons (3.18) 328). 

The isomeric tricyclo[3.3.2.0 ]decane hydrocarbon (396) has also recently yielded to synthesis Thus, reaction of 394a with either thionyl chloride or phosphorus pentachloride led to rearrangement and formation of chloride 395a. Alternatively,... 

In yet another tropone synthesis Skattebol has shown that dibromocyclopropanes carrying a phenolether function react to 1 l-oxa-tricyclo[5.5.0.07,9]undecatrienes when treated with methyllithium. The strained polycyclic intermediate is converted into a 2-alkenyltropone derivative when heated to about 200 °C [137]. 

The construction of the tricyclo[5.2.0.02,6]nonane (26, n = 1) and tricyclo[6.2.0.02,7]decane (26, n = 2) frameworks involved the [2 4- 2] cycloaddition of readily accessible31,32 l,2-bis(trimethyl-siloxy)cyclobutene and cnone 25, n = 1 or 2, respectively.33 The yields (75-80%) were good for adducts 26a, c, e, and g. Lower yields (40-50%) were observed for adducts 26b and 26f, while adduct 26d was only isolated in a trace amount. The most interesting and important reaction, related to the total synthesis of eudesmane sesquiterpenes, was the photochemical reaction of (-)-piperitone (25g) with l,2-bis(trimethylsiloxy)cyclobutene, which gave c/.v,(5wf/u W-2/j,7/i-dimethyl-4/ -isopropyl-l f ,8Jf -bis(triniethylsiloxy)tricyclo[6.2.0.0z 7]dec-3-one (26g) with the relative cis configuration of the methyl (R2) and isopropyl (R3) groups.33,34 Some of the other photochemical [2 + 2] cycloaddition reactions utilizing l,2-bis(trimethyl-siloxy)cyclobutene are shown by the formation of 2735,36 and 28.37... 

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. 

Intramolecular [2 + 2] photocycloadditions of 3-alkenylcyclopent-2-enones represent the key step in the total synthesis of various natural products, e.g. pentalenolactone 6-methyl ester19 and pentalenic acid,20 as well as in the preparation of strained fenestranes21 and laurenene.22 Similarly, the photoisomerization of 3-alkenylcyclohexcnoncs to tricyclo[6.3.0.01-6]undecanones are steps in the syntheses of tricyclic sesquiterpene isocomene23 and precursors to members of the acorane family.24... 

In cycloadditions of enones to alkenes novel strategies have been adopted for ring expansion of the cycloadducts, either by the choice of appropriate alkenes, e.g. 2-(trimethylsiloxy)buta-1,3-diene,70 vmv-2-trimethylsiloxybuten-2-oales71 or 3,3-dimethylcyclopropene,72 or by using 3-oxo-l-cyeloalkene-l-carboxylates as enones.73 Asymmetric [2 + 2] photocycloaddition of cyclopent-2-enone to a (+ )-dihydrofuran acetonide constitutes the cornerstone of the synthetic strategy in the first total synthesis of the novel antitumor metabolite ( )-echinosporin.74 The cycloaddition product 25 from treatment of 2-(2-carbomethoxyethyl)-2-cyclopentenone (24) with ethene has been used as a precursor for the preparation of tricyclo[4.2.0.01,4]octane.75... 

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... 

The Wolff rearrangement has been very successfully used in the synthesis of propellanes.40 The highly strained 3-diazo[3,2.2]propellan-2-one was photolyzed in dichloromethane at — 70 °C in the presence of dimethylamine to give A W-dimethyl tricyclo[2.2.2.0 u4]octane-2-carboxamide (5), a very highly strained interesting compound with inverted geometry at the bridgehead carbons,42 in 40% yield.41... 

CYCLOPROPENE A NEW SIMPLE SYNTHESIS AND ITS DIELS-ALDER REACTION WITH CYCLOPENTADIENE (Tricyclo[3.2.1.02>4]oct-6-ene, (1a,2a,4a,5a)-)... 

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