Propellanes radical reactions

Most alkyl chlorides are not active enough to react with propellanes. However, carbon tetrachloride g m-trichlorides and sulfonyl chlorides react easily to give the first few oligomeric derivatives of [ ]staffanes. The radical reaction of la with sulfuryl chloride yields the expected oligomers [/i]30 but also the compounds 31 and 32 are formed in 12% and 8% yield, respectively... 

Homoquinones are also prepared by a variety of methods that involve the free-radical reactions of propellanes with benzoquinones, ° the Michael addition of suUbxonium methyhde" and ethyl cyanoac-etate anion to naphthoquinone and of sulfonium methyhdes to benzoquinones, the photooxygenation of norcaradienes, the reaction of diethoxyphthalans with quinones, and the Diels-Alder reactions of siloxy- and alkoxy-substituted furans with cyclopropenes. ... 

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... 

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). 

Before proceeding to a discussion of the reactions of the central bond of [1.1.1] propellane, it will be useful to describe the properties of the first-formed intermediates, the bicyclo[l, l.l]pent-l-yl anion 16, radical 6, and cation 19. 

Radical attack on the central bond in [1.1.1 [propellane 1 occurs 2-3 times faster than attack on styrene96 and yields bridgehead bicyclo[l.l.l]pent-l-yl radicals6. Laser flash photolysis techniques were used to measure the rate constants for the reactions of la with five different radicals (Table 12)96"99. The addition of the phenylthiyl radical to la is... 

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

Reactions with carbonyl compounds. The reaction of acetaldehyde with [1.1.1]-propellane turned out differently than anticipated, and yielded the formal 1 2 adduct 37a 8 64,110 (Scheme 3). It has been proposed64-110 that the radical 38 (R = MeCO) adds to the carbonyl group instead of abstracting the aldehydic hydrogen, and the resulting oxy... 

Sometimes the isolation of individual members of the series is not an issue, as in polymer synthesis. Pure neat propellane polymerizes spontaneously in a matter of hours at room temperature. The process can be suppressed by dilution with a solvent or addition of a small amount of a radical inhibitor. Although a possible catalytic role of impurities and Teflon-coated container walls has not been ruled out completely rigorously, it appears likely that this may be a genuine example of a process in which two closed-shell molecules react to produce a biradical which then triggers oligomerization and polymerization. A SINDOl computational study has led to the proposal that the reaction proceeds through a [2]staffane-3,3 -diyl triplet formed by the interaction of two monomers followed by intersystem crossing . ... 

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