I. The RCM approach towards 1,6-methano-bridged[12] & [14]annulenes and their bisdehydro-derivatives. II. 1,5-bisdehydro[10]annulene revisited
Item
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Title
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I. The RCM approach towards 1,6-methano-bridged[12] & [14]annulenes and their bisdehydro-derivatives. II. 1,5-bisdehydro[10]annulene revisited
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Identifier
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d_2009_2013:7e4de08f9d9c:10339
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identifier
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10575
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Creator
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Chen, Yor-Yu,
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Contributor
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Klaus G. Grohmann
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Date
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2010
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Language
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English
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Publisher
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City University of New York.
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Subject
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Organic chemistry | Aromatic | Enediyne
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Abstract
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Part I of my dissertation presents a new efficient synthesis of 3,4-benzo-1,6-methano[12]annulene (3). This novel synthetic approach involves a grignard addition to 3,4-benzo-cycloheptatriene-1,6-dialdehyde followed by a ring closing olefin metathesis (RCM) reaction giving the bridged 12-menber ring of 3,4-benzo-1,6-methano[12]annulene (3) was obstained in six steps and an overall yield 44%. This allowed the complete structural and spectroscopic characterization as a paratropic ethano-bridged benzo[12]annulene with a 28% reduction of the paramagnetic ring current relative to the non-benzannulated molecule. A careful comparison of the 1H NMR of (3) with its 9,10-dihydro derivative (104) suggests an extended paratropic 16pi system. The RCM approach is general and thus formally presents a 6 steps route to the parent 1,6-methano[12]annulene, previously reported by E. Vogel et al. Combination of cis-selective Wittig reaction of (36) with the ylide derived from 4-bromo-1-butene followed by RCM reaction yielded the 9,12-dihydro-3,4-benzo-1,6-methano[14]annulene (35). Attempts to convert this molecular in to the expectedly diatropic 14pi system did not succeed so far. In course of this investigation, an efficient synthesis for 3,4-benzo-1,6-ethynylcycloheptatriene was developed. Diketone (37) obtained through Jones oxidation of the diasteromeric alcohols (26) was converted into the 3,4-benzo-1,6-methano-7,12-bis(dibromomethylene)-8,11-dihydro[12]annulene (38). Treatment of this molecule with two moles of n-butyllithium did not yield the anticipated diacetylene (39). From diketone (37) a series of 7,12-disubstituted bridged [12]annulene can be synthesized, this illustrating the generality of this approach.;In part II of my dissertation, approaches toward 1,5-bisdehydro[10]annulenes were investigated with the goal to increase the activation energy for the known Bergmann rearrangement or even mark it impossible for the molecule to undergo it. This would enable us to investigate the expected 10pi aromaticity of the 1,5-bisdehydro[10]annulene system. An initial approach utilizing the Ramberg Bakelund rearrangement failed due to the irreproducibility of the formation of the cyclic sulfide (70). Elimination was the major pathway even at pH8, most likely due to the very acidic propargylic hydrogens. The second approach started with the 10 menber ring diyneacetals (78), (85), (91). In course of this investigation a new reaction sequence was discovered as outline on scheme 3-9. This valuable fragmentation deprotection of stable cyclic benzylidene acetals leads directly to allylic alcohols such as compound (86). The introduction of the last double bond via the mesylate followed by treatment with potassium t-butoxide gave unexpectedly Benz(a)anthacene (89) and tetracene (88) in a ratio of 40:1. This result is being interpreted as an initial acetylene-allene isomerization followed by an allene-acetylene cyclization (Myers-Saito cyclization), hydrogen abstraction and aromatization as shown on scheme 3-14. Treatment of the mesylate (93) derived from the allylic alcohol with potassium t-butoxide gave phenanthrene and anthracene in a ratio of 2:3. Treatment of the mesylate with triethylamine gave only anthracene, the expected product of the Bergmann rearrangement.*.;*Please refer to dissertation for diagrams.
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Type
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dissertation
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Source
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2009_2013.csv
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degree
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Ph.D.
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Program
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Chemistry
