Synthesis of new molecular systems

Abstract

The versatile cyclopropene synthon 1 -bromo-2-chlorocyclopropene has been used to synthesize new di-and tricycloproparenes. Treatment of these cycloproparenes with silver ion in chloroform leads to rapid oligomerization via carbocation intermediates to give materials in which the aromatic systems are connected by six-membered rings. The ladder polymer formed by treating the linearly fused dicyclopropanaphthalene with silver ion in chloroform has been characterized by solid state nuclear magnetic resonance spectroscopy.The manufacture and manipulation of structures at the molecular level have been recognized as important goals for more than thirty years (1). The synthesis of linear rigid molecules composed primarily of six-membered rings (molecular lines) is of interest in this regard. Miller and his co-workers have prepared short molecular lines composed of polyacenequinone units via repetitive Diels-Alder reactions (2,3). The Diels-Alder reaction has also been identified as a route to other novel belts or collars (4-9). In this manuscript we summarize our recent work on the synthesis of six-membered rings using cycloproparenes (10) as starting materials.The reaction is exemplified below using the simplest cycloproparene, benzocyclopropene 1. Other examples in which benzocyclopropenes have been dimerized by silver ion in chloroform to yield dimers connected by six-membered rings are presented in Table 1.

Cycloproparenes

“…However, the provision of such derivatives by dimerization of lower members of the series has been achieved (see section IIIA). 101 If an appropriate multiple cissoid diene is available then there appears to be almost no limit to the way in which the cycloproparene moiety can be incorporated into organic structures. Thus, Billups 102 has show that the symmetrical tricycloproparenes 76 and 77 (Chart 1) can be obtained from hexaradialene 85 and hericene 86, respectively, by way of 3-fold Diels-Alder cycloadditions with 60.…”

“…63,206 Silver(I) also promotes the addition of alkenes, alkynes, allenes, and conjugated dienes to cyclopropabenzene as has been discussed earlier, 15 and this ion, Cu(II), and Hg(II) have been used in the dimerization of 2. 101,207,208 Nonetheless, it is the use of Ag(I) in the linear dimerization of the cycloproparenes that now commands most attention. 100,101,103,209 In 1974, Billups 207 showed that Ag(I) effected smooth dimerization of 2 to 9,10-dihydroanthracene.…”

Aryl-substituted methylidenecyclopropa[b]naphthalenes: synthesis and attempted silver(I)-mediated dimerization

“…Rather, the first derivatives were subjected to silver(I) in methanol in a study 23 that predates the dimerization work of Billups. [15][16][17][18] To date this gap has not been bridged. Thus complexation of, e.g.…”

“…That the reaction conditions employed herein are appropriate for dimerization has been confirmed from successful dimerization of 3 to 6,13-dihydropentacene in 73% yield. 15,17 The steric constraints present at C1 of the exocyclic alkenes 1-5 (and disilane 4) are too large to allow dimerization as only products of ring opening (or unchanged starting material) are recorded .…”

“…4 The Ag(I)-mediated opening is particularly efficacious, as illustrated by its use in the characterization of 1H-cyclopropa [b]naphthalene-3,6-dione, 14 but it is its application to the dimerization of the cycloproparenes that has commanded much recent attention. [15][16][17][18] For the simple cycloproparenes, the dimerization reaction entails the dropwise addition of an anhydrous chloroform solution of the cycloproparene to a suspension of AgBF 4 (ca. 1 mol %) in the same solvent at 0 o C. 15 Such reactions are usually complete within a few minutes and, as the anhydrous non-nucleophilic solvent cannot intercept the σ complex, a second equivalent of cycloproparene binds with the ring-opened cation ultimately to yield cycloproparene dimer (Scheme 1).…”