Systematic Structural Modification of a Pentacyclic Helical Tubuland Host Diol

Ahn, Paul D.; Bishop, Roger; Craig, Donald C.; Downing, Gary A.; Scudder, Marcia L.

doi:10.1071/c97073

Cited by 4 publications

(5 citation statements)

References 2 publications

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“…Treatment of diketone 31 with methylmagnesium chloride is known to give only the anti , syn ‐ (36%) and anti , anti ‐diol (62%) isomers 36. It was therefore necessary to prepare the required syn , syn isomer 17 by a different route (Scheme ).…”

Section: Resultsmentioning

confidence: 99%

Molecular Solids Formed by the Self-Organisation of Dialcohols into Hydrogen-Bonded Ladders

et al. 2001

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The ability of certain dialcohols to form solid‐state structures containing unidirectional hydrogen‐bonded ladders has been investigated. Two double‐stranded structures, staircase‐ladders and step‐ladders, have been identified. In each, dialcohol molecules are hydrogen‐bonded into linear strands with two parallel strands cross‐linked through additional hydrogen bonding. Staircase‐ladders are made up of (O−H)n chains of hydrogen bonds, with the molecules in the two strands out of phase with each other. Step‐ladders are formed from (O−H)4 cycles of hydrogen bonds, with the molecules of the two strands in phase. Sixteen examples of staircase‐ladder structures and twelve cases of step‐ladder structures were identified by use of the Cambridge Structural Database. A further three examples, all shown to be staircase‐ladders by single‐crystal X‐ray analysis, were synthesised. Distinct structural preferences in ladder formation can be identified. Nearly all staircase‐ladders contain only one type of enantiomer, with the dialcohol building blocks arranged around a twofold screw axis. This type of ladder is thus favoured for enantiomerically pure compounds. The preferred step‐ladder construction contains (+)‐enantiomers in one strand and (−)‐enantiomers in the other, giving two repeating centres of symmetry along the ladder axis. There are, however, many exceptions to this norm. These two ladder types are compared with each other and with those formed by organic molecules containing other hydrogen‐bonding functionalities.

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Section: Resultsmentioning

confidence: 99%

Molecular Solids Formed by the Self-Organisation of Dialcohols into Hydrogen-Bonded Ladders

et al. 2001

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“…Unfortunately, the methylation step (Scheme ) is indiscriminate and requires separation of all three diol products. Greatly improved facial selectivity was achieved by Paul Ahn in the analogous reaction of ethano-bridged dione 25 , and the product 26 is also a HT diol . Both 24 and 26 have a rigid skeleton with no possibility of the conformational mobility present in the previous HT diols.…”

Section: Pentacyclic Cage Ht Diolsmentioning

confidence: 99%

“…Greatly improved facial selectivity was achieved by Paul Ahn in the analogous reaction of ethano-bridged dione 25, and the product 26 is also a HT diol. 27 Both 24 and 26 have a rigid skeleton with no possibility of the conformational mobility present in the previous HT diols. Unlike the rigid compounds 6 and 7, however, their pentacyclic skeletons contain built-in twist that satisfies the requirements of MD (b).…”

Section: Pentacyclic Cage Ht Diolsmentioning

confidence: 99%

Helical Tubuland Diols: A Synthetic and Crystal Engineering Quest

Bishop

2008

Acc. Chem. Res.

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Despite many advances in recent years, crystal engineering remains a risky venture. A successful outcome requires manipulation of the noncovalent bonding and properties such as size, shape, repulsion, attraction, polarity, and chirality. In this Account, we describe the interplay of crystal engineering and synthetic organic chemistry required to develop the family of helical tubuland diol hosts, the members of which exhibit a wide range of tube dimensions and inclusion properties. Certain alicyclic dialcohols crystallize with a hydrogen-bonded network structure, termed the helical tubuland lattice, in space group P3(1)21 (or its enantiomorph P3(2)21). Double helices of diol molecules surround parallel tubes that contain guest molecules, which are included on the basis of size and shape rather than functional group. The crystal structure of (diol)(3).(chloroacetic acid)(1.2) is illustrative. These chiral helical tubulate lattice inclusion compounds are formed when the racemic host diol is allowed to crystallize from solution. Complete enantiomer separation occurs during this process, producing a 1:1 mixture of pure (+)- and pure (-)-crystals (a conglomerate). The challenge of creating this family of compounds required the development of much synthetic chemistry, in particular new pathways to alicyclic ring systems with specific substitution patterns. It was also necessary to understand and control the supramolecular properties of the diol molecules. What makes the original compound tick, and why did it behave in this remarkable manner, when most of its structural neighbors crystallize totally differently? The synthesis of new helical tubuland diols requires not just preparation of a new molecular structure but also a transplant of the original unchanged hydrogen-bonding supramolecular synthon. Synthesis of the specific crystal space group is necessary. This was achieved by defining structural characteristics, termed molecular determinants, which are essential for the helical tubuland structure to occur. If these requirements were met, then the target molecule had a high probability of success. This investigation has close conceptual parallels with the search for pharmacophore properties of bioactive molecules. In both situations, parts of a molecule with little or no chemical reactivity may actually play vital supramolecular roles. The review illustrates how crystal engineering is based on specific supramolecular properties that can be uncovered and then exploited by synthetic chemists.

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“…In another well-investigated system Bishop and Dance et al have found a remarkable diol host system for which stringent variants repeatedly adopt a porous morphology. However, even here of thirteen studied derivatives of the host compound, seven form noninclusion solid-state structures. ,− Furthermore, it is often challenging to predict the substituent effect on the final structure. A good illustration of this is the Bishop and Dance system for which the methyl derivative is porous whereas the hydrogen and ethyl derivatives are not …”

Section: Introductionmentioning

confidence: 99%

“…However, even here of thirteen studied derivatives of the host compound, seven form noninclusion solid-state structures. 34,[43][44][45][46][47][48] Furthermore, it is often challenging to predict the substituent effect on the final structure. A good illustration of this is the Bishop and Dance system for which the methyl derivative is porous whereas the hydrogen and ethyl derivatives are not.…”

Section: Introductionmentioning

confidence: 99%

Variable Pore Size, Variable Chemical Functionality, and an Example of Reactivity within Porous Phenylacetylene Silver Salts

et al. 1999

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Investigations on molecular variants of the 3-fold symmetric 1,3,5-tris(4-ethynylbenzonitrile)benzene crystallized with silver triflate revealed a nearly invariant pseudohexagonal porous structure type. Modifications involved the attachment of pendant groups to the central aromatic ring of the parent molecule. Pendant groups include the vinyl group, stilbene, the chiral group myrtanol, and groups with different chemical functionalities such as alcohols, ethers, and esters. Modifications also included the addition of elongated spacer units between the central benzene ring and the peripheral nitrile groups. In these molecules the acetylene bridges of 1,3,5-tris(4-ethynylbenzonitrile)benzene were replaced with diacetylene, ethynylbenzene, and diethynylbenzene type units. Single-crystal refinements for pentoxy-2,4,6-tris(4-ethynylbenzonitrile)benzene·AgOTf and 1,3,5-tris(4-(4-ethynylbenzonitrile)phenyl)benzene·AgOTf as well as powder data on 12 crystalline phases showed the consistent formation of pseudohexagonal channels, demonstrating that the parent porous architecture is stable both to functional modification of the interior of the channel as well as to enlargement of the pores. Pentoxy-2,4,6-tris(4-ethynylbenzonitrile)benzene·AgOTf refined in the monoclinic space group Am. 1,3,5-Tris(4-(4-ethynylbenzonitrile)phenyl)benzene·AgOTf was found to be triclinic with space group P1̄. These crystals have pseudohexagonal channels respectively 15 and 25 Å in diameter. Cell constants based on powder data are compatible with channel diameters ranging from 10 to 30 Å. The latter channel diameters are among the largest known for organic porous solids. The introduction of the chiral myrtanol unit led to the preparation of a chiral porous solid. The thermal and chemical stabilities of these phases were investigated. The pseudohexagonal structure proved stable to complete solvent loss from the channel. It was found in the case of a host with alcohol functionality that an acid anhydride guest, trifluoroacetic anhydride, reacted with the host to form an ester with retention of the porous structure type.

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Systematic Structural Modification of a Pentacyclic Helical Tubuland Host Diol

Cited by 4 publications

References 2 publications

Molecular Solids Formed by the Self-Organisation of Dialcohols into Hydrogen-Bonded Ladders

Molecular Solids Formed by the Self-Organisation of Dialcohols into Hydrogen-Bonded Ladders

Helical Tubuland Diols: A Synthetic and Crystal Engineering Quest

Variable Pore Size, Variable Chemical Functionality, and an Example of Reactivity within Porous Phenylacetylene Silver Salts

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