Quinodi methanes

An interesting example of the application of the theory is a prediction of a new route to polyamantane by polymerization of -quinodi-methane 121h The first step would be n-n overlapping interaction. The HO and LU of quinodimethane are indicated in Fig. 7.40 a. The mode of n HO-LU interaction and the possible structure of polyamantane derived therefrom (Type I polymer) can be seen in Fig. 7.40b. On the other hand, the direction of the hybridization change would be controlled by the a-n interaction. The nodal property of n HO and a LU of the monomeric unit are as shown in Fig. 7.40 c, so that the hybridized states of carbon atoms might change into the form illustrated in Fig. 7.40d to lead to the Type II polymer. 

Pyrrole-fused 3-sulfolenes 221 undergo thermal extrusion of sulfur dioxide to produce highly reactive o-quinodi-methanes which can be trapped in Diels-Alder reactions (Scheme 23) <1997H(46)199, 1997TL3639>. The resulting cycloadducts 222-227 are important starting compounds in porphyrin synthesis. 

Tetrahydroisoquinoline undergoes a thermal retro-Diels-Alder reaction to give o-quinodi-methane (Equation 13). 

The first Diels-Alder [4+2]-cydoaddition functionalization of CNTs has been reported recently [171]. Ester-functionalized SWCNTs were reacted with o-quinodi-methane, generated in situ from benzo-l,2-oxathiin-2-oxide under microwave irradiation (Scheme 1.23). This technique opened up a new access to a novel family... 

Grosch B, Orlebar CN, Herdtweck E, Massa W, Bach T (2003) Highly enantioselective Diels-Alder reaction of a photochemically generated o-quinodi-methane with olefins. Angew Chem 115 3822-3824, Angew Chem Int Ed 42 3693-3696... 

TEA(TCNQ)2 [triethy lammonium-di(7,7,8,8-tetracyano-p-quinodi-methane)], a one-dimensional semiconductor... 

Fused O-heterocycles, synthesis via pericyclic reaction of o-quinodi-methanes 88YGK1179. 

The corresponding transformation of cis-benzocyclobutene (610) to (612) proceeded slower (by a factor of 27), in keeping with the involvement of an ( ,Z)-intermediate (611). Attempts to generalize the latter type of stereochemistry met with only limited success due to the propensity of ( ,Z)-o-quinodi-methanes for 1,5-shifts (e.g. S, Scheme 134) and cyclizations. 

Various o-quinodi methanes, generated in situ from o-alkenylbenzyltributyl-stannane precursors, have been used to synthesize functionalized polycycles by Diels-Alder reaction with maleic anhydride, methylacrylate, dimethylfumarate and N-phenyl maleimide in the presence of electrophiles [37] (Scheme 2.16). 

Thieno-o-quinodi methanes 46 and 48, generated in situ by iodide-induced 1,4-elimination from the respective 2,3-bis(chloromethyl)thiophene 45 and 2,3-bis(bromomethyl)benzo[b]thiophene 47 precursors, undergo Diels-Alder... 

Bis-o-quinodi methanes have also been used to functionalize [60]-fullerene by Diels-Alder reaction. An example is the preparation of main-chain polymers with incorporated [60]-fullerene units [48] illustrated in Scheme 2.20. Cycloaddition of bis-diene 50 generated in situ from bis-sulfone 49 with [60]-fullerene leads to an oligomer mixture 51. Another type of functionalization is based on the... 

In a series of papers, Kametani and co-workers reported that o-quinodi-methanes are sufficiently reactive dienes to combine with neutral, elec-ton-rich cyclic and acyclic imines to produce Diels-Alder adducts.64-67 In all cases, the o-quinodimethane was generated by thermal opening of a substituted benzocyclobutene. Several examples of the transformations which could be effected are shown in Scheme 2-X. 

The undoubted highlight of the year in triterpenoid synthesis is the paper by Kametani and his colleagues which describes the full details (see Vol. 8, p. 174) of a stereoselective synthesis of the pentacyclic intermediates (132) and (133), used by Ireland in his syntheses of alnusenone and friedelin. This paper also includes a short non-stereoselective synthesis of (132) and (133) (see the Scheme). The key step is an intramolecular cycloaddition of the o-quinodi-methane intermediate (130). 

PhTeNa) reacts with a,a -dichloro-o-xylenes to give O-quinodi-methanes and although this reaction should also be catalytic in tellurium, best results were observed with the use of two equivalents... 

Volume 1 contains 15 chapters on the recent developments in charge-transfer salts, fullerenes, photoconductors and molecular conductors. The topics covered include electron acceptor molecules, photo-induced intermolecular electron transfer systems, perylene based conductors, tetrachalcogenafulvalenes, metal 1,2-dichaIcogenoIenes and their conductive salts, conductive hetero-TCNQs (tetracyano-p-quinodi-methane derivatives), molecular metals and superconductors based on transition metal complexes. 

A few scattered examples of intramolecular Diels-Alder cycloadditions of nitriles have been documented. Oppolzer has synthesized some benzo-cyclobutene nitriles (Scheme 6-III) and found that on pyrolysis they were transformed into isoquinoline derivatives in excellent yields. o-Quinodi-methanes are assumed to be transient dienes in all of these cycloadditions. 

It should be noted that while particularly advantageous for the above reactions with quinone derivatives, the Pd-mediated generation of indolo-2,3-quinodi-methanes is not suitable when acetylenic dienophiles are used, as both DMAD (221) and methyl propiolate (370) tend to undergo Pd-catalyzed trimerizatiOTi reactions. Nevertheless, the approaches developed by Mukai and coworkers offer an elegant and useful access route to a variety of indolo-2,3-quinodimethanes and their subsequent Diels—Alder reactirm products. 

Laronze M, Sapi J (2002) 3-Cyanomethyl-2-vinylindoles as thermal indole-2, 3-quinodi-methane equivalents synthesis of functionalized 1, 2, 3, 4-tetrahydrocarbazoles. Tetrahedron Lett 43 7925-7928... 

Benzocyclobutenes have been found to ring open to very reactive o-quinodi-methanes (<9-xylylenes) which can be trapped by various dieneophiles. Huisgen showed that the cis- and ra/i5 -3,4-diphenyl-l,2-benzocyclobutenes give the trans-and c/5 -3,6-diphenyl-4,4,5,5-tetracyano-l,2-benzocyclohexanes, respectively, when treated with tetracyanoethylene (TONE), in a first-order reaction independent of the concentration of TCNE (Scheme 9.24)." ... 

The varied uses of highly dipolar cyano-substituted quinodi-methanes has stimulated much synthetic interest as shown above, especially in the preparation of aryl-substituted malononitriles as potential precursors. A three-step synthesis of these compounds has been developed without use of arylation methodology (cf. above). Aroyl halides were treated sequentially with cyanotri-methylsilane and POCl - both in the presence of pyridine - to... 

In addition to the nature of the initiation process, several questions remain concerning the homopolymerization of p-quinodi-methane. The suggested mode of propagation involving biradical coupling0 remains to be established Concerning termination it has been pointed out that hiradical coupling is not a true termination, but apparently no one has considered radical disproportionation as shown in equation 6. 

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