Quadricyclanes, rearrangement

Orchard, S.W. and Kutal, C., Photosensitization of the norbomadiene to quadricyclane rearrangement by an electronically excited copper(l) compound, Inorg. Chim. Acta, 62, 95-96,1982. 

The skeletal rearrangement of various strained cyclic compounds is carried out with a catalytic amount of soluble complexes of PdCl2. Namely, the rearrangements of bulvalene (67) to bicyclo[4.2.2]deca-2,4,7,9-tetraene (68)[54], cubane (69) to cuneane (70)[55], hexamethyl Dewar benzene (71) to hexa-methylbenzene (72)[56], and 3-oxaquadricyclanes[57] and quadricyclane (73) to norbornadiene[58-60] take place mostly at room temperature. Reaction of iodocubane (74) with a terminal alkyne catalyzed by Pd(0) and CuBr unexpectedly affords an alkynylcyclooctatetraene 75, without giving the desired cubylalkyne 76. Probably the rearrangement is a Pd-catalyzed reaction[61]. 

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... 

Haselbach et al. [9] also classified radical electrocyclic reactions in the three types shown in Fig. 2, but were the first to point out that formally state-forbidden radical ion reactions can be extremely facile because state crossings can occur at very low activation energies. The principles outlined were used to analyze the rearrangement of the quadricyclane radical cation, 1, to the norbor-nadiene radical cation, 2, a reaction that occurs at extremely low temperatures in Freon matrices [10]. 

The pathway via the lithio quadricyclane intermediate failed due to an unexpected rearrangement presented in Fig. 2.16. 

Optical spectroscopy has merits in identifying radical cations, particularly when their spectra are known independently. For example, the radiolysis of quadricyclane led to the observation of the known spectrum of norbornadiene radical cation. In another study, irradiation of cyclooctatetraene radical cation caused the color of the sample to change from bright red to royal blue, suggesting the conversion to a different species, the previously identified semibullvalene radical cation. Further irradiation of the latter led to a characteristic banded (vibrationally resolved) spectrum the nature of this spectrum suggested that the rearranged species may be a linear conjugated radical cation and helped in its identification as 1,4-dihydropen-talene radical cation. ... 

The process is induced photochemically and involves the single-electron transfer oxidation of cubane then completed with a backward electron transfer to the transient radical cations. A Li+ salt with a weakly coordinating anion is able to induce pericyclic transformations, including the rearrangement of cubane to cuneane, quadricyclane to norbomadiene, and basketene to Nenitzescu s hydrocarbon 392... 

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-cyclo-addition reactions (76JA6057) of cyclopropanoid hydrocarbons, e.g. bicyclo[n.l.O]alkanes, has been discussed. 

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 opposite substrate-induced diastereoselectivity is observed in the cycloadditions to norbor-nenc and norbornadiene, since the adducts exo-9 and endo-10 are obtained, respectively6. The e.w-adduct 10, prepared from norbornene, can also be obtained, together with a rearrangement product, by cycloaddition to quadricyclane followed by double-bond hydrogenation8. 

Treatment of P3C3Bu 3 with [(CO)sW <—PMe], generated / si/u by thermal decomposition of 56b (R = Ph) at 110°C, furnished a 2 1 mixture of quadricyclane 58b and the tricyclic compound 59, which were separated by fractional crystallization as colorless or yellow crystals in 39% and 25% yield, respectively. The presence of a three-membered ring in 59 agrees with an initial attack of the phosphinidene complex at a P=C bond of the triphosphinine to give transient 60. An intramolecular electrophilic aromatic substitution furnished product 59, whereas rearrangement of 60 to tetraphosphanorbornadiene 57a and its intramolecular [2+2] cycloaddition would rationalize the formation of 58b (Scheme 22) <2001CEJ3545>. 

A method to synthesize amino sulfoxides 212 and 213 was developed based on the rearrangement of sulfinamides 211300 (equation 81). The adduct of phenyl sulfonylamine and quadricyclane, i.e. 1,2-thiazetidine-A-oxide 214, underwent smooth rearrangement to furnish the fused 1,4-thiazine-A-oxide 215301 (equation 82). 

Silver(I) ions generally catalyze the rearrangement of strained polycyclic systems which contain cyclopropane groups. It was shown, however, that silver(I) cleaved one or two of the strained cyclopropane bonds in quadricyclane (13) in an oxidation reaction. A complex mixture was obtained on treatment of quadricyclane (13) with silver(I) trifluoroacetate. The main addition products contained two oxygen functions and one intact cyclopropane ring." °... 

Chlorination of cyclopropane in the dark in a sealed tube at 35 °C in the presence of a catalytic amount of iron gave 1,3-dichloropropane (5) and 1,2-dichloropropane (6) as the major products. Diethylaminosulfonyl hypochlorite underwent addition across one of the most strained C — C bonds of quadricyclane to give a mixture of two stereoisomeric nortricyclane derivatives 7 and 8 and one rearrangement product 9. ... 

In the case of quadricyclan-3-ones 21, the cycloadducts 22 immediately extrude carbon monoxide and rearrange to cyclooctatetraene derivatives 23. ... 

Both the acid induced and the photochemical rearrangement of the norbornaidiene derivative (146) affords the hydroxynaphthalene (147). The photo-process is not affected by triethylamine and it is thought to involve benzy lie-ally lie C-O bond cleavage. No evidence was put forward for the intermediacy of a quadricyclane. Prinzbach smd his coworkers have reported the synthesis of the oxanorbornadienes (148) and their photoconversion into the corresponding oxaquadricyclane derivatives (149) on irradiation. The azaquadricyclanes (150) have been prepared by the irradiation of the corresponding norbornadiene derivatives (151). ... 

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