Propellanes reactions

In contrast to the [5.3.1]propellanes, reaction of chloro[4.3.1]propellene 33 or dihalo[4.3.1]propellane 34 with t-BuOK yielded Dewar benzene isomer 35 of... 

Elimination of HCl from 1-cholorquadricyclane (121) leads to transient olefin 122, which can be captured by anthracene to furnish the highly substituted [4.2.1]propellane 123. The X-ray structure of 123 indicates that the bridgehead carbon atoms of the propellane system are very slightly inverted the plane of the three starred substituents of the nearer bridgehead passes 0.05 A behind the bridgehead. The necessary rehybridization is apparently sufficient to lead to typical propellane reactions, and 123 adds thiophenol readily to form 124 . Related adducts form with substituted anthracenes. The parent [4.2.1]propellane is also known and is little more reactive than bicydo[2.1.0]hexane from which it is formally derived... 

The coupling of 1,8-diiodonaphthalene (25) with acenaphthylene (26) affords acenaphth[l,2-a]acenaphthylene (27). It should be noted that the reaction involves unusual trans elimination of H—Pd—1[32], This tetrasubstituted double bond in 11 reacts further with iodobenzene to give the [4, 3, 3]propellane 28 in 72%. This unusual reaction may be accelerated by strain activation, although it took 14 days[33]. 

The propellanes are highly reactive substances which readily undergo reactions involving rupture of the central bond. It has been suggested that the poh erization of propellanes occurs by a dissociation of the central bond ... 

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." ... 

At the same time, the reaction of CCl3Br with 1,1,1-propellane gives mostly the adduct, even when the propellane excess is used (ref. 14) ... 

Proceeding the reaction of bromocyane with 1,1,1-propellane differ essentially from that for CCl3Br (ref. 14). In the case of bromocyane telomers CN-( ) -Br... 

Bridgeheads. The Sn2 mechanism is impossible at most bridgehead compounds (p. 392). Nucleophilic attack in [l.l.l]propellane has been reported, however. In general, a relatively large ring is required for an SnI reaction to take place (p. 396). " The SnI reactions have been claimed to occur for l-iodobicyclo[l.l.l]pentane via the bicyclo[l.l.l]pentyl cation, but this has been disputed and the bicyclo[1.1.0]butyl carbinyl cation was... 

The cycloaddition reaction of heterocyclic propellanes 99 (X = O and S) with iV-phenyltriazolinedione (NN) (Fig. 16) affords the anti adduct with respect to the bridge [166-168]. Replacement of the a-CH groups by carbonyls (that is 100),... 

Synthesis of the propellane (4) requires FGA. With two four-membered rings probably to be made by photochemical reactions, a carbonyl group on the six-membered ring is best, allowing a 2 + 2 disconnection. 

Two illustrations that show the power of this reaction for the preparation of strained cycloalkenes are the contractions of 102 to the propellane 103 , an application that has been reviewed , and of 104 to the bicyclo[2.1.1]hexene 105 . The utility of the Ramberg-Backlund rearrangement in the preparation of various natural products such as steroids , terpenoids and pheromones has been demonstrated. In addition to the synthetic applications mentioned in the previous subsection, several selected examples taken from the recent literature are given in equations 66-69. These examples further demonstrate the potential of this method for alkene synthesis in general. 

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... 

To emphasize this statement I should like to begin with a heterocyclic case which provides an outlet for the molecule s behavior that leads to neither propellane or spiran albeit, on paper, both of these types might be expected to form. In Mulheim/Ruhr the following reaction was studied ... 

Often there are two (or more) courses that a reaction may take, say, cyclization of a common starting material (under whatever conditions that are being used) leading to several possible products. In this chapter, I want to discuss just such a case where cyclization of a generalized l,i,2,2-tetrasubstituted ring 4 may lead to a propellane 5... 

We tried in 1968, as it turned out, unsuccessfully, to prepare a propellane having the [4.2.2] nucleus (actually it was a [4.2.2]propellene). But we were most successful in preparing the isomeric dispiran 7. None of the desired propellane was formed (see reaction scheme) ... 

The spiroketone 28 was converted into its tosylhydrazone whose sodium salt 29 was heated without solvent in a high vacuum. The bicyclic olefin 30 was formed and being a cyclobutene, Woodward and Hoffmann allowed it to ring-open to afford 31 and these two products were collected in a trap cooled by liquid nitrogen. When the mixture was permitted to warm up, an exothermic reaction (again allowed by W H) set in and the cyclobuteno[4.2.2]propellane 32 was formed11. ... 

In the Baeyer-Villiger oxidation of [4.3.3]propellane-8,ll-dione 74 the propellane-bis-lactones formed, 75 and 76, are accompanied by a dispirolactone 77 22. Different product mixtures result when different (acidic or more basic) reaction conditions are employed but it has been shown experimentally for the head-to-tail propellane bis-lactone 75, vis-a-vis the isomeric dispiran 77, the latter appears to be the thermodynamically more stable product, resulting from the former under acidic conditions (p-TsOH/ C6H6, 7 days, r.t.). The structures were established by means of X-ray diffraction and H- and 13C-NMR spectroscopy. 

For a review of these compounds until 1975, cf. Ginsburg, D. Propellanes. Structure and Reactions , Verlag Chemie, Weinheim, 1975, pp. 30-53... 

The action of t-butyllithium on 5-methylene-8-nonenyl iodide (206) leads to the lithium compound 207, which undergoes a tandem cyclization to yield eventually 84% of 2-methylspiro[4.4]nonane (208) (equation 102). An analogous reaction of the iodide 209 (equation 103) results in the [4.3.3]propellane 210 (81%) as a mixture of endo- and excMSomers1. ... 

For n = 1, this is the standard synthesis of [l.l.l]propellane 40a.20,21 Also for n = 3, this method makes [3.1.1]propellane 40c accessible with reasonable effort.22 Although [2.1.1]propellane 40b was detected by its IR spectrum at liquid nitrogen temperature,23 it could not be obtained as a stable compound via this route.22 The addition of halomethanes across the central bond by a radical chain mechanism is common to 40a and 40c. The addition of carbon tetrabromide to 40c afforded a 45% yield of 41.18 Likewise, a number of bicy-clo[l.l.l]pentane derivatives 42 were obtained by reaction of the corresponding halomethanes with 40a.17,24... 

Precursors for this task were obtained by addition of /-butylmagnesium bromide to the central bond of [1.1.1 ]propellane 40a followed by conversion of the 3-f-butylbicyclo[ 1.1.1 Jpentyl-1 -y 1-magnesium bromide (88) into the ketones 89 by standard methods.27 Reaction of ketones 89 with tosyl hydrazide afforded the hydrazones 90, which gave the corresponding lithium salts 91 by reaction with MeLi in ether. These salts were dried under high vacuum and then pyrolized at 4 x 10 5 torr in the temperature range of 100-130°C and the volatile products condensed in a liquid nitrogen-cooled trap. 

Iterative trapping of the alkylpalladium species with tethered olefins is also possible, which allows tandem cycloisomerizations and zipper reactions to take place. Thus, depending upon the juxtaposition of the unsaturated bonds, Trost achieved highly atom-economical syntheses of triquinanes, propellanes (264) from the ynediene 263, and polyspiranes (Scheme 67).261... 

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. 

Many reducing agents are capable of severing a carbon-halogen bond. Cathodic cleavage provides perhaps the most versatile method, and has been put to excellent use. The electrochemical variation of the Wurtz reaction constitutes a powerful method for the construction of a variety of rings, particularly strained systems. Dramatic examples are provided by the assembly of bicyclobutane (308) [89], bicyclohexene (310) [90-92], [2.2.2]propellane (312) [93], spiropentane (316) [94], j -lactams 318 [95], and a variety of small-ring heterocycles (320) [96,97]. 

The reaction of EtsSiH with [l.l.l]propellane under photolytical decomposition of di-tert-butyl peroxide afforded products 17 and 18 in 1 3 ratio (Reaction 5.15) [36]. A rate constant of 6.0 x 10 M s at 19 °C for the addition EtsSi radical to [l.l.l]propellane was determined by laser flash photolysis [37]. Thus, it would appear that [l.l.l]propellane is slightly more reactive toward attack by EtsSi radicals than is styrene, and significantly more reactive than 1-hexene (cf. Table 5.1). 

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