Propellanes cycloaddition

An interesting synthetic method for the [3.3.3]propellane 74 by intramolecular cycloaddition of a disubstituted methylenecyclopropane with an iinsa-... 

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),... 

When exposed to ultraviolet light, dienes 411 and 412 undergo intramolecular [2+2] cycloaddition. The latter reaction provides a particularly convenient synthetic entry to [3.3.2]propellane from a readily available starting material... 

A synthesis of the 11-aryl-1 l-aza[5.3.1 ]propellan-2-one 29 was accomplished by the intermolecular cycloaddition of the cycloheptenone 26 with an aryl azide. The... 

Addition to six-membered oxygen heterocycles is also common. The photocycloaddition of 5,7-dimethoxycoumarin to tetramethylethylene has been described,269 and 4-hydroxycoumarin (326) undergoes facile addition to cyclohexene on direct irradiation to give the cyclobutane (327)270 analogous additions to a variety of other alkenes have been reported, and the cycloaddition of 4-methoxycoumarin to 2-methylpropene has been employed in a synthesis of l,2-dihydrocyclobuta[c]coumarin.271 Photoaddition of the 1,2-bisenol lactone (328) to tran.s-stilbene yields propellane (329),272 and [ 2 + 2] cycloaddition is observed along with other competing photoreactions on irradiation of chromone in the presence of alkenes.273... 

Propellane derivatives are available via intermolecular meta cycloaddition. Compounds 106 [81,82] and modhephene 107 [81] were obtained using this type of photocycloaddition (Sch. 21). Isoiridomyrmecin 108 [83] and decarboxyquadrone 109 [82] can be synthesized via the same photochemical key step. 

Steric and electronic effects are responsible for the diaslcrcoselectivity observed in the Diels Alder cycloaddition of 4-methyl- and 4-phenyl-3/f-l,2,4-triazole-3,5(4//)-dione to propellanes (Table 4). The dienophile can approach the diene syn or anti, i.e., above or below the plane, respectively. 

Intramolecular exocyclic transannular cycloaddition of TMM can provide a viable route to propel-lanes, such as the sesquiteipene modhephene (144). TTiis methodology is demonstrated in an efficient synthesis of a [3.3.3]propellane (145) (equation 149)." The methylenecycloprtqtane approach is preferred in this case because it works well with dialkyl-substimted systems. 

Methano[10]annulene has been prepared through the intermediacy of several [5.3.1]propellanes. The first of these, [5.3.1]propella-2,4,7-triene 23 was prepared by carbene addition to the trienone (22) . It is capable of undergoing [2-h2], [4-f2] and [6-h2] cycloaddition... 

Another husband-wife team (cf. Ref. 72a) has prepared 2,4-methano-2,4-de-hydroadamantane which contains a [3.1.1]propellane moiety (88) by intramolecular cycloaddition, of 87 " . (One may muse about what it is that attracts such teams to smallring propellanes. Imagine what great progress there might have been had Mrs Wiberg entered this field ) C-chemical shifts of the inverted carbons was discussed " (cf Ref 74c). 

A combination of a photochemical [2 -i- 2] cycloaddition of dichloroethylene to enone (4), followed by a reductive elimination, was used to prepare the tricyclic cyclobutene (5), which served as a precursor to the highly strained 8-carboxy[6]paracyclophane (6 Scheme 2). A similar strategy has been used to prepare other strained propellanes. ... 

The diene part of tricyclo[5.3.1.0]undeca-2,4,9-triene (6), however, is in the synperiplanar conformation, hence, in some cases, a Diels-Alder reaction with the dienophile is observed. Depending on the dienophile, the unsaturated propellane undergoes three different modes of cycloaddition. 

A less reactive bicyclo[3.2.0]hept-l(7)-ene substructure has been found in 164 (149). This compound was prepared from propellane 163 by photolysis and subsequent reduction. In contrast to 163, irradiation of the parent tricyclic ketone 165 in ethanol gives the saturated ketone 167. The formation of 167 is taken as evidence for the intermediate formation of the ketone 166. When 168 was treated with CsF in the presence of 1,3-diphenylisobenzofuran, an adduct was isolated, which was assigned the structure of the expected [2 + 4]cycloaddition product of 169 (150). 

An interesting synthetic target related to triptindane is the tris(naph-tho)[3.3.3]propellane 86 (Schemes 16 and 17). Alder et al. [84] reported on first attempts to construct this two-fold triptindane bearing a highly strained C - C bond. Cyclodehydration of acenaphthenediol 85, prepared previously from acenaphthene quinone (84) [85], or the corresponding pinacolone formed as an intermediate in the acidic medium, did not occur in the desired way (Scheme 16). Attempts to utilize the corresponding bis(dihydro) derivative (i.e. the diol derived from 87) resulted in the formation of the C2-symmetrical polycycle 88, possibly by di-oxy Cope rearrangement followed by a criss-cross [2 + 2] cycloaddition [84]. 

Ein besonders interessantes Beispiel ist das 1,2,5,6-Tetrabis-[methylen]-cyclo-octan, bei dem neben der stufenweisen Cycloaddition je zweier benaehbarter Doppelbindungen noch ein Cydobutan-RingschluB zu einem Propellan-System erfolgt5 ... 

The cyclopentenones (70) do not undergo cycloaddition reactions with cyclohexene. The only reaction encountered in the irradiation of these molecules is the facile isomerization by a 1,3-alkyl shift to (71). In contrast with this, irradiation of cyclopentenone (72a) in the presence of ethylene yields (73a). The cyclopentenone (72b) yields (73b) with cyclohexene. It is clear from these results that there is some structural phenomenon within the molecules which make some, the (4,3,2)-propellanes prone to rearrange, while others, the (3,3,3)-propellanes, undergo cycloaddition. 

In an interesting variation of the above cycloaddition reactions, it has been reported that W-methylcycloalkano[b]indoles 181 undergo a regioselective 1,3-dipolar cycloaddition with 2,6-dichlorobenzonitrile oxide (182) to give the corresponding propellanes 183 in moderate to good yields [82] (Scheme 51). 

More recently, the reaction was found to give an 87 13 mixture of the dimethylenecyclopropane and vinylidenecyclopropane, which is invariant with the extent of reaction and appears to be an equilibrium mixture of the two (Scheme 6.9). Further, the activation parameters for loss of the propellane were determined to be log k = 14.02 - 39 660/23RT The reaction appears to resemble the retro 2 + 2 cycloaddition of bicydo[1.1.0]butanes. 3-Methylenecyclobutene was also formed as a result of heterogeneous catalysis. 

Aue found that [3.2.1]propellane opened to 1,3-dimethylenecyclohexane at 318°C (Scheme 9.100)/ The temperature necessary to affect this retro 2 + 2 cycloaddition is much higher than that for the retro 2 + 2 cycloaddition of [2.2.2]propellane to 1,4-dimethylenecyclohexane studied by Eaton which occurs at only 25°C/ ... 

Tetracyclo[4.2.1.0/ 0 ]decane undergoes a retro 2 + 2 cycloaddition at high temperatures (325°C) in contrast to the same reaction of [2.2.2]propellane which reacts at room temperature (see Chapter 9, Section 4) (Scheme 11.98)/ ... 

In the course of these mechanistic studies a number of propellanes have been prepared. Paquette has used the route via a-chlorosulphones described last year to prepare a series of substituted [4,4,2]propellanes. Pyrolysis of triene (267) affords the cyclo-octatetraene (268) and similarly (269) gives (270). Labelling studies show that rearrangement proceeds via an intramolecular +, 2J cycloaddition followed by valence isomerization. Further Diels-Alder additions to (271) and related propellanes are described, and the e.s.r. spectrum of the radical obtained by electrolytic reduction of (272) is recorded. Other important synthetic studies concern [4,2,l]propellanes, [4,3,1]-propellanes, and [4,2,2]propellanes. ... 

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