10-Monosubstituted-bicyclo

Rhodium(I)-catalysed Pauson-Khand reaction of allenynes has been shown to be applicable for constructing azabicyclo[5.3.0]decadienone and oxabicyclo[5.3.0] decadienone frameworks. The 10-monosubstituted-bicyclo[5.3.0] deca-l,7-dien-9-one ring system has been prepared by the rhodium(I)-catalysed Pauson-Khand reaction of allenynes under 10 atm of CO (Scheme 86).129... 

The cobalt(I)-catalysed 6 + 2-cycloadditions of cyclooctatetraene with monosubsti-tuted alkynes produced monosubstituted bicyclo[4.2.2]deca-2,4,7,8-tetraenes in good yields.185 The 6 + 3-cycloaddition of fulvenes (145) with 3-oxidopyrylium betaines (144) formed 5-8 fused oxa-bridged cyclooctanoids (146,147), which can be manipulated by cycloaddition reactions to produce key intermediates (148,149) for the synthesis of fused cyclooctanoid natural products e.g. lancifodilactones (Scheme 38).186,187... 

Bicyc/o-[6,1,0]- and -[5,2fi]-nonanes. Lanthanide-induced shift n.m.r. of 9-anti- and 9-syn-monosubstituted bicyclo[6,l,0]nonatrienes demonstrates that the extended... 

The 4-alkenyl /3-sultams 50 and 51 can be prepared by stereoselective alkylation of the 4-monosubstituted /3-sultams 68 with alkenyl halides. Reaction of product 50 with ethylaluminium dichloride in toluene gives the aldehyde 69. When /3-sultam 51 is used, a tandem cyclization is observed yielding the bicyclo[3.2.1] 7-sultam 70 (Scheme 12). In the... 

Oxymercaration (2, 265-267 3. 194). Brown and Geoghegan have investigated the relative reactivities of a number of olefins in the oxymercuration reaction in a 20 80 (v/v) mixture of water and THF. The following reactivity is observed terminal disubstituted > terminal monosubstituted > internal disubstituted > internal trisub-stituted > internal leirasubstitu ted. Thus steric factors play a major role in the reactivity of olefins. Increased substitution on the double bond and increased steric hindrance at the site of hydroxyl or mercury substituent attachment decrease the rate of reaction. In the case of olefins of the type RCH CHR, cts-oleiins are more reactive than the corre.sponding rra/i.s-olefins. Inclusion of the double bond in ring systems causes a moderate rate increase which varies somewhat with structure cyclohcxenc > cyclo-pentenc cyclooctene norbornene bicyclo[2.2.2]-octene-2. 

An unprecedented cyclopropanation reaction was observed during the reaction of ketene alkylsilyl acetals (191) with bromoform-diethylzinc. When monosubstituted acetals were used, cyclopropanecarboxylic esters (195) were formed by a novel C-H insertion. When disubstituted ketene acetals were used, byproducts such as a,)5-ethylenic esters (197) were also formed presumably via 196 (equation 49). This reaction provides a convenient method for the preparation of the bicyclo[3.1.0] hexane system and can be advantageously compared to the copper-catalysed intramolecular cyclization of unsaturated a-diazoketones . 

Photolysis of a-diazo esters in the presence of benzene or benzene derivatives often results in [2-1-1] cycloaddition of the intermediate acylcarbene to the aromatic ring, thus providing access to the norcaradiene (bicyclo[4.1.0]hepta-2,5-diene)/cyclohepta-l,3,5-triene valence equilibrium. The diverse effects that influence this equilibrium have been discussed (see Houben-Weyl, Vol. 4/3, p509). To summarize, the 7-monosubstituted systems obtained from a-diazoacetic esters exist completely in the cycloheptatriene form, whereas a number of 7,7-disubstituted compounds maintain a rapid valence equilibrium in solution. On the other hand, several stable 7-cyanonor-caradienes are known which have a second 7t-acceptor substituent at C7 (see Section 1.2.1.2.4.3). Subsequent photochemical isomerization reactions of the cycloheptatriene form may destroy the norcaradiene/cycloheptatriene valence equilibrium. Cyclopropanation of the aromatic ring often must compete with other reactions of the acylcarbene, such as insertion into an aromatic C H bond or in the benzylic C H bond of alkylbenzenes (Table 7). 

Replacement of bis(l,2-diphenylphosphino)ethane by chiral phosphanes such as (— )-(25, 3 5)-bis(diphenylphosphino)butane or (- -)-(/ )- ,2-bis(diphenylphosphino)propane allows a highly enantioselective cobalt-catalyzed homo-Diels-Alder reaction (maximum 91% ee) between norbornadiene and monosubstituted alkynes. Similarly, the reaction of norbornadiene with phenylacetylene in the presence of catalytic amounts of tris(acetylacetonato)cobalt and (-l-)-bicyclo[2.2.1]hept-5-ene-2,3-diylbis(diphenylphosphane) leads quantitatively to the homo-Diels-Alder adduct with an ee of 98.4%. ... 

Deuterium isotope effects have been studied for the Diels-Alder reactions between hexadeuterio-monosubstituted cyclo-octatetraenes (283) and several reactive dieno-philes leading to adducts (284). With dicyanomaleimide, isomerization of the cyclo-octatetraene to the bicyclo[4,2,0]octa-2,4,7-triene is the rate-determining step, but with the less reactive dienophiles (maleic anhydride and tetracyanoethylene) larger... 

A somewhat more complex case is rqvesented by the two, stereoisomeric bicyclo[3.3.0]octanes shown below. The AS values for each of the monosubstituted compounds (endo- or exo-2-methyl, endo- or exo-3-hydroxy, and exo-6-methyl) can be added to find a predicted total effect. These values can then be added to the shift values of the parent to arrive at a predicted absorption for each of the framework carbons. In this case the predictions are generally close to the observed spectrum so long as the substituents do not interact with each other either sterically or electronically. 

The same problem occurs with the bicyclo[3.3.1]nonane system when there is an endo substituent at both C-3 and at C-7 resulting in a double twist boat conformation. Since each of the model, monosubstituted compounds will be predominately in a boat - chair arrangement, they will not serve as good sources for A6 effects for the disubstituted system and their use results in sizable orors for C-3 and C-7. 

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