Sumanene

Sumanene is a polycyclic aromatic hydrocarbon and of scientific interest because the molecule can be considered a fragment of buckminsterfullerene. Suman means "sunflower" in both Hindi and Sanskrit.^[1] The core of the arene is a benzene ring and the periphery consists of alternating benzene rings (3) and cyclopentadiene rings (3). Unlike fullerene, sumanene has benzyl positions which are available for organic reactions.

Additional recommended knowledge

How to ensure accurate weighing results every day?

Correct Test Weight Handling Guide: 12 Practical Tips

What is the Correct Way to Check Repeatability in Balances?

Organic synthesis

The structure of Sumanene can be inferred from oxidation of 1,5,9-trimethyltriphenylene but the first practical synthesis starts from norbornadiene.^[2] Norbornadiene is converted into a stannane by action of n-butyllithium, dibromoethane and tributyltinchloride. A Ullmann reaction of this stannane with CuTC affords the benzene core. The methylene groups created in this conversion then migrate in a tandem ring-opening metathesis and ring-closing metathesis by the Grubbs' catalyst. The final structure is obtained by oxidation by DDQ.

Properties

Sumanene is a bowl shaped molecule with a bowl depth of 1.18 angstroms (118 picometers).^[3] The 6 hub carbon atoms are pyramidalized by 9° and the molecule displays considerable bond alternation (138.1 to 143.1 pm). Sumanene also experiences bowl-to-bowl inversion with an inversion barrier of 19.6 kcal/mol (82 kJ/mol) at 140 °C which is much higher than that found for its corannulene cousin. Like any benzylic proton, the sumanene protons can be abstracted by a strong base such as t-butyl lithium to form the sumanene mono carbanion. This strong nucleophile can react with an electrophile such as trimethylsilylchloride to the trimethylsilyl derivative.

References

1. ^ Towards the design of tricyclopenta [def, jkl, pqr] triphenylene (sumanene): a bowl-shaped hydrocarbon featuring a structural motif present in C₆₀ (buckminsterfullerene) Goverdhan Mehta, Shailesh R. Shahk and K. Ravikumarc Journal of the Chemical Society, Chemical Communications, 1993, (12), 1006 - 1008 Abstract
2. ^ A Synthesis of Sumanene, a Fullerene Fragment Hidehiro Sakurai, Taro Daiko, and Toshikazu Hirao Science, Vol 301, Issue 5641, 1878 , 26 September 2003 Abstract
3. ^ Structural Elucidation of Sumanene and Generation of Its Benzylic Anions Hidehiro Sakurai, Taro Daiko, Hiroyuki Sakane, Toru Amaya, and Toshikazu Hirao J. Am. Chem. Soc., 127 (33), 11580 -11581, 2005 Abstract