Quadricyclane cycloaddition reactions

Quadricyclane is a highly strained and reactive compound. It reacts readily with acetic acid to give a mixture of nortricyclyl acetate and exo-norbornyl acetate and with bromine to yield a mixture of 2,6-dibromonortricyclene and exo-5-anti-l-dihvo-monorbornene.3 Quadricyclane undergoes cycloaddition reactions with a variety of dienophiles to give 1 1 adducts.15 1 2 3 4 5 6 7... 

It appears likely that transient metallacyclobutanes are involved in a variety of organic reactions which are catalyzed by transition metal complexes. Thus, cycloadditions of activated alkenes to strained hydrocarbons such as quadricyclane and bicyclo[2.1.0]pentane are catalyzed by complexes such as Ni(CH2=CHCN)2 and probably involve initial formation of a nickelacyclobutane (Scheme 2) (79MI12200). The nature of the organometallic intermediates in related metal-catalyzed rearrangements (72JA7757) and retro-cycloaddition reactions (76JA6057) of cyclopropanoid hydrocarbons, e.g. bicyclo[n.l.O]alkanes, has been discussed. 

Cycloaddition reactions of triplet excited 1,4-quinones to ground-state alkenes occur either via a triplet exciplex intermediate, which collapses to a triplet biradical,1000 or via separated radical ion intermediacy.990 The existence of biradical intermediates has been proven by measurements of chemically induced dynamic nuclear polarization (CIDNP) (Special Topic 5.3), for example in the reaction of 1,4-benzoquinone (313) with norbomadiene (314) yielding two products, the spiro-oxetane 315 and the spiro-oxolane 316 (Scheme 6.139).1001 Interestingly, quadricyclane (317) provides the same reaction as norbomadiene. 

SCHEME 2.22 Cycloaddition reaction of quadricyclane (12) with hexafluorothioacetone and bis(trifluoroniethyl)thioketene. 

Similarly to fluorinated ketones, electrophilic polyfluorinated azines and rmidoyl fluorides undergo [2 + 2 + 2] cycloaddition reaction with quadricyclane (12) to afford fluorinated norbornenazetidines 73-74 (Scheme 2.35). 

Cycloaddition Reactions.—7,7-Difluoronorbomadiene and its quadricyclane isomer have been synthesized by the route shown in Scheme 23. The quadricyclane is... 

In the presence of transition metal complexes, certain strained hydrocarbon systems are activated under mild thermal conditions and undergo characteristic transformations. Methylenecyclopropane (XXVI) (Noyori et al., 1970, 1972b), bicyclo[2.1.0]pentane (XXVII) (Noyori et al., 1971c, 1974a), and quadricyclane (XXVIII) (Noyori et al., 1975a) add to electron-deficient olefins with the aid of a nickel(0) catalyst such as bis(l,5-cyclooctadiene)-nickel(O) or bis(acrylonitrile)nickel(0). These cycloaddition reactions proceed... 

The Ni -catalysed (2+2) cycloaddition of activated olefins such as acrylonitrile or acrylic acid esters to quadricyclane which gives endo- and exo-substituted products is complicated particularly in the case of 1,2-disubstituted olefins by a competing isomerization of quadricyclane to norbornadiene. Norbomadiene gives identical cycloadducts under these conditions with a similar isomer ratio. Kinetic studies of the cycloaddition reactions of quadricyclane gave a plot of log [quadricyclane]t o/ [quadricyclane]i=t against time which exhibited a marked deviation from linearity due to the retarding effect of norbomadiene which is also formed and in turn coordinates to the Ni catalyst. Scheme 11 accounts for these observations. 

The Co2(CO)8-catalysed tandem 2- -2- -1/2- -2-f 2-cycloaddition reaction of terminal diynes (180) provides a simple one-pot synthesis of novel tetracyclic compounds (181) (Scheme 69). A computational study of the thermal nl + ct2 -I- a 2-cycloaddition of quadricyclane with acetylene, ethylene, DCE, and DMAD... 

Photoinitiated Quadricyclane and Norbornadiene Cycloaddition Reactions and Rearrangements... 

When additional substituents are introduced in the 2- and/or 4-position, the thermal rearrangement gives products in which the substituents that were originally located in the 1- and 5-position of the quadricyclane are then located at C4 and C5 of the oxepin 7.30,123 In order to trap intermediates of this rearrangement reaction by intramolecular cycloaddition vinyl and acetylene groups were linked with different spacer groups to C2 of quadricyclane.123 In this manner two different intramolecular cycloadducts were isolated in addition to oxepin derivatives.123... 

There are several known examples of silenes participating in [2 + 2 + 2] cycloadditions, including reactions with norbornadiene and with quadricyclane. Examples of these reactions with norbornadiene are shown in Eq. (30), where the silene bridges the 2,6-positions.38 5, 53 ,7U85 ,88 This reaction has only been investigated using some of the Auner-type silenes. In many cases mixtures of stereoisomers were obtained, and in some cases products of an ene reaction were also observed. 

The reactions with quadricyclane, shown in Eq. (31), gave products identical to those formed by the same silene reacting in a [2 + 2] manner with norbornene. Mixtures of exo endo isomers were frequently observed. Again, only silenes of the Auner type have been studied with this reagent,51-53,185,188 so it is not known whether the Wiberg- or Brook-type silenes will undergo this mode of cycloaddition. 

Like the cyclization of the parent system, the photocyclization of hetero analogues of norbornadiene was reported many years ago. Recent interest in this area will serve to illustrate the potential of the conversions. Thus the irradiation of the oxanorbomadiene system 259 brings about conversion to the oxepine 260138. The formation of 260 presumably arises by quadricyclane 261 formation, followed by secondary photolytic ring-opening. Other research has shown that irradiation of the oxanorbomadiene 262 follows the same reaction mode and it undergoes (2 + 2)-cycloaddition to the quadricyclane derivative 263. Apparently, in this instance, cycloreversion affords the ylide 264 that can be trapped by suitable addends, giving the adducts illustrated in Scheme 3139. 

The reaction proceeds smoothly and gives 326 in 43% yield. The stereochemistry of the addition is exo with respect to the norbomene moiety and in line with the usual cycloaddition behavior of quadricyclane [358]. The norbomene double bond in 326 is easily accessible by electrophiles, and, for example, the anti-addition of benzenesulfenyl chloride proceeds quantitatively at room temperature (Scheme 4.66). 

Photolysis (> 290 nm) induced quantitative conversion of (20c and d) to the crystalline 3-azaquadricyclanes (22c and d) that isomerize in solution at 20° to the azepines (23c and d) at measurable rates. The azepines rapidly dimerize. The thermally forbidden 47 reversal of 22 to 20 was not observed.80 Prinzbach and Eberbach81 have carried out numerous cycloadditions and acid-catalyzed rearrangements of 22c and d and of 23c and d. The 3-azaquadricyclanes 22 have diene properties but, as valence isomerization to azepines is so easy (above), cycloadditions were achieved only with the very reactive dienophiles DMAD and EP. Reactions with 22c and d at -15° to - 30° over 24 to 48 hours using a large excess of ester gave 24 (R = H or E). If equimolecular proportions of the quadricyclane and ester are used, the products (24) compete as dienophile for example, 24d (R = H) added to 20d to give 25.81... 

The complex Mo(tfd)3 was reported by King and co-workers (86) to catalyze the conversion of quadricyclane to norbornadiene (Eq. 9), polymerization of quadricyclane or norbornadiene, as well as the addition of water to quadricyclane to give nortricyclanol (Eq. 15). The reactions appear to involve pseudo-[4 + 2] cycloaddition to the sulfur atoms in the dithioketone form of the metal... 

The irradiation of the norbornadiene derivatives (148) yields the quadricyclanes (149). These quadricyclanes can be reconverted to the starting material by treatment with silver ion. The norbornadienes (150) photochemically ring close to the quadricyclanes (151). Both direct and sensitized irradiation were used but the direct irradiation afforded a mixture of products. The reactions were much cleaner using benzophenone as the sensitizer. Irradiation of the norbornadiene derivative (152) affords the quadricyclane (153). Paquette and Racherla - have synthesized the norbornadiene (154) in which it is claimed that homoconjugation is high. This is borne out on acetophenone-sensitized irradiation in pentane when it is converted to the quadricyclane (155). Prinzbach and his coworkers have reported on the photochemical (2+2)-cycloadditive behaviour of adducts of the type represented by (156). The acetone-sensitized irradiation of this compound brings about (2 + 2)-cycloaddition to afford a 2 1 mixture of the adducts (157) and (158). Direct irradiation, however, follows a different path to yield a mixture of the (2+2)-adduct (157) as... 

Other cycloadditions proceed in systems where the reaction partners are preoriented with a geometry ideally suited for the cycloaddition and the system is essentially forced towards the desired transition state. Bridged cyclic dimers or oligomers of norbornadiene and quadricyclane (6) serve as molecular frameworks. 

One typical example is given by G. Kaupp with the [2+2] cycloaddition of diphenyl-acetylene to 1,4-dioxene leading to a bicyclic cyclobutene in good yield (cf. iv of this chapter). Another example is presented by T. Miyashi starting from naphthoquinonor-bomadiene. In an intramolecular reaction a quadricyclane derivative is quantitatively formed upon irradiation at X > 400 nm. It is assumed that this process involves the diketo-norbomadiene in its triplet state. Although the spin multiplicity of intermediates have not... 

Figure 2.59 collects several [2t-2]-cycloadditions that can be carried out with C )-The reaction with dehydrobenzene is instructive as it reveals electronic properties of the fullerene The dehydrobenzene generated in situ from anthranilic acid reacts with Cso exclusively in a [2-i-2]-cycloaddition, although in principle a [4-f2]-reaction would also be possible, and dehydrobenzene usually enters into the latter when adding to electron-rich dienes. The nonoccurrence of this reaction clearly shows the electron-deficient character of C,so. For the same reason it never constitutes the diene part in a Diels-Alder reaction. Furthermore, the [24-2]-cycloaddition may be thermally effected, for example, the addition of long-chain cumulenes, allene amides or quadricyclan. The addition of ketenes as well occurs without irradiating the reaction mixture. Normally a reduced reactivity toward C,so should be expected for the electrophilic ketenes, but in reality the products of a [2-1-2]-cycloaddition are even found to be the major product. 

The uncatalyzed reaction of 43 with quadricyclane (12) proceeds readily to give the exo-adduct 46 (Scheme 2.22). Analogous cycloaddition with formation of adduct 47 was also observed for hexafluorothioacetone generated in situ from dithietane 35 (Scheme 2.22). ... 

Petrov, V.A. Davidson, E Smart, B.E. Quadricyclane— thermal cycloaddition to polyfluorinated carbonyl compounds. J. Fluorine Chem. 2004, 725(10), 1543-1552. Petrov, V.A. Stereoselective synthesis of polyfluorinated cxo-tricyclononenes and nor-bomenes. ACS Symp. Ser. 2007, 949 (Current Fluoroorganic Chemistry), 113-140. Gambaryan, N.P. Simonyan, L.A. Petrovskii, P.V. Reaction of fluoro ketones with vinyl esters. Izv. Akad. Nauk SSSR, Ser. Khim. 1967, (4), 918-921. 

Barlow, M.G. Suliman, N.N.E. Tipping, A.E. Unsaturated nitrogen compounds containing fluorine. Part 18. Novel cycloaddition products from the reaction of quadricyclane with fluorinated azines and the azomethine imide 2-hexafluoroisopropylidene-3-methyl-3-phenyl-5,5-bis(trifluoromethyl)tetrahydropyrazol-2-ium-l-ide. J. Fluorine Chem. 1995, 72(1), 147-156. 

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