Abstract:The synthesis and determination of thermo-The spiro-norcaradienes (111) were obtained as previously dynamic parameters are described for spiro-norcara-by photolysis of the corresponding diazo-cyclopentadienes dienes (111) substituted in the norcaradiene 6-membered (V) in trifluoromethylbenzene (VIa) or m-hexafluorodiring.
“…Several spirotropylidenes having the ring structure shown as 1 were synthesized by Dürr and co-workers almost 30 years ago. , Although these compounds possess 10 π-electrons and so might be regarded as homoaromatic, they are actually rather unstable. NMR studies showed that all of the compounds of type 1 were in equilibrium with their spironorcaradiene valence isomers ( 2 ). , To our knowledge, no heteroatom-containing rings of type 1 or 2 have appeared in the literature. 1 …”
A silaspirotropylidene, 5, has been
obtained
from the reaction of the lithium salt of tetramethylsilole
dianion (3) with 2 equiv of
diphenylcyclopropenone,
followed by quenching with Me3SiCl. The X-ray
crystal
structure of 5 indicates that the five-membered ring
is
planar and the silepine ring adopts a boat conformation.
“…Several spirotropylidenes having the ring structure shown as 1 were synthesized by Dürr and co-workers almost 30 years ago. , Although these compounds possess 10 π-electrons and so might be regarded as homoaromatic, they are actually rather unstable. NMR studies showed that all of the compounds of type 1 were in equilibrium with their spironorcaradiene valence isomers ( 2 ). , To our knowledge, no heteroatom-containing rings of type 1 or 2 have appeared in the literature. 1 …”
A silaspirotropylidene, 5, has been
obtained
from the reaction of the lithium salt of tetramethylsilole
dianion (3) with 2 equiv of
diphenylcyclopropenone,
followed by quenching with Me3SiCl. The X-ray
crystal
structure of 5 indicates that the five-membered ring
is
planar and the silepine ring adopts a boat conformation.
“…Although these compounds possess 10 π-electrons and so might be regarded as homoaromatic [3], they are actually rather unstable. NMR studies showed that all of the compounds of type 1 were in equilibrium with their spironorcaradiene valence isomers (2) [2,4].…”
mentioning
confidence: 99%
“…A possible pathway for the formation of *8* and *9* is proposed.Several spirotropylidenes having the ring structure shown as 1 were synthesized by Durr and co-workers almost 35 years ago [1,2]. Although these compounds possess 10 π-electrons and so might be regarded as homoaromatic [3], they are actually rather unstable.…”
Reaction of 1,1-dilithio-2,3,4,5-tetraphenylsilole (*5*) with diphenylcyclopropeneone proceeds with loss of silicon to yield the dilithium salt of 2,3,4,5-tetraphenyl-1,4-hysroquinone (*8*), which was trapped with trimethylchlorosilane to yield 1,4-bis(trimethylsiloxy)-2,3,5,6-tetraphenylbenzene, *9*. A possible pathway for the formation of *8* and *9* is proposed.Several spirotropylidenes having the ring structure shown as 1 were synthesized by Durr and co-workers almost 35 years ago [1,2]. Although these compounds possess 10 π-electrons and so might be regarded as homoaromatic [3], they are actually rather unstable. NMR studies showed that all of the compounds of type 1 were in equilibrium with their spironorcaradiene valence isomers (2) [2, 4].To our knowledge, only one heteroatom-containing ring of type 1 has appeared in the literature [5]. A silaspirotropylidene, 4, was obtained from the reaction of the lithium salt of tetramethylsilole dianion (3) with 2 equiv of diphenylcyclopropenone, followed by quenching with Me 3 SiCl (Scheme 1).Recent studies have made anions and dianions of siloles readily available [6]. We report here the reaction of the tetraphenylsilole dianion 5 with 2 equiv of diphenylcyclopropenone to give 2,3,5,6-tetraphenylbenzene dianion 8. Subsequent quenching with Me 3 SiCl produced pale-yellow crystals of 9 (isolated yield 37%, based on starting ketone, Scheme 2). [7−10] The X-ray crystal structure of 9 is shown in Figure 1. 1 H, 13 C, and 29 Si NMR spectra of 9 in solution are consistent with the 1,4-bis(trimethylsiloxy)-2,3,5,6-tetraphenylbenzene structure. However, weak signals were observed in the 29 Si NMR spectrum of the crude product at δ = 17.18 and 17.57 ppm; one of these may belong to 1,2-bis(trimethylsiloxy)-3,4,5,6-tetraphenylbenzene as a minor product in this reaction.It is difficult to rationalize the surprising formation of 9, but one possible mechanism is suggested in Scheme 3. Two successive nucleophilic reactions of the negatively charged silicon of the silole dianion 5 on the ring carbons of the cyclopropenone molecule (at the C C and then the C O double bonds or the reverse of this sequence) could take place to give 6. Ring opening to a diradical followed by ring closure and rearrangement might then take place to produce the seven-membered ring compound 7. Extrusion of the silole moiety could then lead to 8, and thence to 9. 11 Conclusions 1,4-bis(trimethylsiloxy)-2,3,5,6-tetraphenylbenzene, 9, has been obtained from the reaction of the lithium
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