Propellanes formation

In a modified procedure the free carboxylic acid is treated with a mixture of mercuric oxide and bromine in carbon tetrachloride the otherwise necessary purification of the silver salt is thereby avoided. This procedure has been used in the first synthesis of [1.1.1 ]propellane 10. Bicyclo[l.l.l]pentane-l,3-dicarboxylic acid 8 has been converted to the dibromide 9 by the modified Hunsdiecker reaction. Treatment of 9 with t-butyllithium then resulted in a debromination and formation of the central carbon-carbon bond thus generating the propellane 10." ... 

When the bicyclic thiirene oxide 180164 is dissolved in excess furan, a single crystalline endo-cycloadduct (182) is formed stereospecifically (equation 71)164. This is the first propellane containing the thiirane oxide moiety. Clearly, the driving force for its formation is the release of the ring strain of the starting fused-ring system 180. In contrast, 18a did not react with furan even under forcing conditions. 

Catalyst 70 is very effective for the reaction of terminal alkenes, however 1,1-disubstituted olefins provide hydrosilylation products presumably, this is due to steric hindrance [45]. When a catalyst with an open geometry (78 or 79) is employed, 1,1-disubstituted alkenes are inserted into C-Y bonds to give quaternary carbon centers with high diastereoselectivities (Scheme 18). As before, initial insertion into the less hindered alkene is followed by cyclic insertion into the more hindered alkene (entry 1) [45]. Catalyst 79 is more active than is 78, operating with shorter reaction times (entries 2 and 3) and reduced temperatures. Transannular cyclization was possible in moderate yield (entry 4), as was formation of spirocyclic or propellane products... 

Although we are dealing with work described in the literature by means of a posteriori molecular calculation it is useful to see the relative calculated heats of formation of the isomeric propellanes and dispirans and note particularly the right-most columns so as to be in a position to gauge these against the experimental results or vice versa. 

The yields of the tetrathia[6.6. l]propellane 60 and of the spirodithiabieyclo[5.4.0]-undecane 63 are only 25% and 18%, respectively. Perhaps this is the manifestation of the relative difficulty in formation of medium rings. It is not otherwise obvious why the yields should be so low. Of course propellanes with larger rings exist but the medium ring isn t cyclized at the bicyclic stage. It is already there 16). 

When the ketone (280) was heated at reflux with pTsOH in benzene, the product (281) was isolated 95). The mechanism of this intriguing rearrangement may involve 1,3-hydride shift or epoxide formation 9S), This reaction appears to be an efficient method for the synthetis of [3.3.3]propellane. 

The initial dimerization presumably leads to a [2.2.2]propellane derivative that undergoes thermolysis to the diene that is the observed product. The dimerization occurs in dilute solutions, but at higher concentrations, polymers are found. This finding is in accord with the proposal that these reactions occur via initial formation of a 1,4-diyl, which closes to form the cyclobutane ring. In this way, the reaction avoids an orbital symmetry disallowed pathway. The diyl could react with the alkene at higher concentrations to give a polymer. 

Bicyclo[2.2.0]hex-l(4)-ene (8) is one of the most highly strained of the alkenes (SE = 87, OS = 35)50 that can be observed at room temperature.51 In dilute solution, it undergoes moderately rapid dimerization at room temperature, presumably giving the pentacyclic propellane 9 as an intermediate in the formation of the diene 10. 

TABLE 13. Formation of bicyclo[l.l.l]pentanes and [n]staffanes by reaction of [1.1.1 ]propellanes with radicals... 

Additions across the C—H Bonds. Many compounds with an activated CH bond, such as cvanoacetic esters or chloroform, oligomerize with propellanes in ethereal solution48,59,101,104107109. However, since diethyl ether itself can add across its activated a C—H bonds48,62,64, mixtures can result, and some of the oligomerization reactions, such as the reaction with formate esters48,59, are best performed in a hydrocarbon solution48,59,104 105, or without any solvent62,64 "0. 

The reaction of the weakly electrophilic 2-nitrophenylsulfenyl chloride with [1.1.1]-propellane produces a complex mixture of products, and the cyclobutanone 48 has been isolated in 10% yield (equation 21). The formation of the product has been attributed to the presence of oxygen in the reaction mixture65 126. 

Propellanes are sensitive to acids. Protonation of [ 1.1.1 Jpropellane with acetic acid yielded 3-methylenecyclobutyl acetate (5)315. The formation of 3-methylenecyclobutyl... 

Coxon, Steel, and co-workers studied the transformations of a series of phenylalk-anols in fluorosulfuric acid at low temperature to find a variety of reaction modes. Cyclization of 2-phenylethanols, in most of the cases, is accompanied by rearrangement to afford various polycyclic products.319 The formation of propellane 86 was rationalized by the plausible mechanism shown in Eq. (5.123). 

This chapter will cover eliminations of HX, X2 and XSiR3 (X = halogen) which lead to the formation of cyclopropenes, bicyclobutanes and propellanes and aspects of other elimi-... 

Based on trapping experiments with -butylamine and dicyclohexylphosphine the formation of the propellane has been proposed to occur through radical intermediates128b. 

In what follows, we will estimate the enthalpies of formation of tetrahedrane and of [l.l.l]propellane by assuming, perhaps disingenuously, that these species are normal and they belong to various homologous series that contain one or the other of these two hydrocarbons. Then, using the enthalpies of formation for the earlier members of these series, we will predict the desired gas phase enthalpies of formation. Although we remember the often given admonition that it is easier to interpolate than to extrapolate, we will nonetheless look at several... 

Reaction 14 is endothermic by 37 kJ mol1, and provides additional documentation for the earlier enunciated superstrain [37] for bicyclobutane. Accepting this value as a correction term for equation 13 gives our first estimate of the enthalpy of formation of gaseous [l.l.l]propellane, namely 349 kJ mol1. We may recognize reactions 13 and 14 as part of a homologous series in which the next and last reaction is... 

This non-reaction reaction is precisely thermoneutral. Linear extrapolation from equations 14 and 15 suggests that equation 13 should be endothermic by 2 37 kJ mol1 and so the enthalpy of formation of [1.1. l]propellane would thus be expected to equal 386 kJ mol1. 

This admittedly nonreaction reaction is, of course, precisely thermoneutral. Linear extrapolation suggests that reaction 16 should be endothermic by twice 44 kJ mol 1 and so the enthalpy of formation of [l.l.l]propellane should be 370 kJ mol1. 

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