Five bicyclo[3.3.0]octa-2,6-dienes

Abstract

A series of five compounds containing the bicyclo[3.3.0]octa-2,6-diene skeleton are described, namely tetramethyl cis,cis-3,7-dihydroxybicyclo[3.3.0]octa-2,6-diene-2,4-exo,6,8-exo-tetracarboxylate, C(16)H(18)O(10), (I), tetramethyl cis,cis-3,7-dihydroxy-1,5-dimethylbicyclo[3.3.0]octa-2,6-diene-2,4-exo,6,8-exo-tetracarboxylate, C(18)H(22)O(10), (II), tetramethyl cis,cis-3,7-dimethoxybicyclo[3.3.0]octa-2,6-diene-2,4-exo,6,8-exo-tetracarboxylate, C(18)H(22)O(10), (III), tetramethyl cis,cis-3,7-dimethoxy-1,5-dimethylbicyclo[3.3.0]octa-2,6-diene-2,4-exo,6,8-exo-tetracarboxylate, C(20)H(26)O(10), (IV), and tetramethyl cis,cis-3,7-diacetoxybicyclo[3.3.0]octa-2,6-diene-2,4-exo,6,8-exo-tetracarboxylate, C(20)H(22)O(12), (V). The bicyclic core is substituted in all cases at positions 2, 4, 6 and 8 with methoxycarbonyl groups and additionally at positions 3 and 7 with hydroxy [in (I) and (II)], methoxy [in (III) and (IV)] or acetoxy [in (V)] groups. The conformations of the methoxycarbonyl groups at positions 2 and 4 are exo for all five compounds. Each C(5) ring of the bicyclic skeleton is almost planar, but the rings are not coplanar, with dihedral angles of 54.93 (7), 69.85 (5), 64.07 (4), 80.74 (5) and 66.91 (7) degrees for (I)-(V), respectively, and the bicyclooctadiene system adopts a butterfly-like conformation. Strong intramolecular hydrogen bonds exist between the -OH and C=O groups in (I) and (II), with O...O distances of 2.660 (2) and 2.672 (2) A in (I), and 2.653 (2) and 2.635 (2) A in (II). The molecular packing is stabilized by weaker C-H...O(=C) interactions, leading to dimers in (I)-(III) and to a chain structure in (V). The structure series presented in this article shows how the geometry of the cycloocta-2,6-diene skeleton changes upon substitution in different positions and, consequently, how the packing is modified, although the intermolecular interactions are basically the same across the series.

Different crystal forms of a rich hydrogen bond acceptor compound resulting from alternative C–H⋯O and orthogonal CO⋯CO molecular interaction patterns

“…The published crystal structure of tetraester 3 (Polymorph I) 34 involves an awkwardly shaped concave face to concave face dimer. Repetition of this unit results in a simple crystal packing arrangement in which only two types of weak intermolecular awkward repeat unit of Polymorph I, which alerted us to the packing difficulties of 3, 1,24 is abandoned in these new structures.…”

“…The racemic C 2 -symmetric tetraester 3 is obtained from reduction of Schroeter and Vossen's Red Salt 27,28 using sodium amalgam 29 or, more simply, by condensation of one equivalent of glyoxal with two equivalents of dimethyl 3-ketoglutarate. [30][31][32] Crystallisation of 3 from methanol 33 or acetone 34 gave identical crystals that showed indications of inefficient packing in the solid state. We have a long-standing interest in the crystal structures of alicyclic diols and especially those that exhibit inclusion properties.…”

“…The P2 1 /n crystal structure of 3 (Polymorph I) Crystallisation of racemic 3 from either methanol 33 or acetone 34 at room temperature gave highly crystalline material in space group P2 1 /n that is free of included solvent (Polymorph I). The molecule 3 adopts a shape like a shallow dish with a handle.…”

“…These data are those for the published structure. 34 Fig. 1 The molecular conformation adopted by the tetraester 3 in Polymorph I crystals.…”

Solvent–guest control of two extremely similar tetrahydrofuran inclusion structures

“…The racemic form of 2,4,6,8tetracarbomethoxybicyclo[3.3.0]octa-2,6-diene-3,7-diol (1) is obtained easily by condensation of one equivalent of glyoxal and two of dimethyl 3-ketoglutarate (Bertz et al, 1990). Crystallization of racemic (1) from acetone yielded solventfree crystals in space group P2 1 /n (Vega et al, 2008). In these crystals the dish-shaped tetraester has assembled into a centrosymmetric dimer by utilizing two identical C-HÁ Á ÁO-C weak hydrogen bonds.…”