3δ2-Chromene (2,3-Didehydro-2H-1-benzopyran): Generation and Interception

Christl, Manfred; Drinkuth, Stefan

doi:10.1002/(sici)1099-0690(199802)1998:2<237::aid-ejoc237>3.0.co;2-6

Cited by 23 publications

(17 citation statements)

References 38 publications

Supporting

Mentioning

Contrasting

Unclassified

Order By: Relevance

“…[6±8] The role of allene 6 and biradical 7 is, however, unclear. [9,10] At higher temperatures, processes including the intermediates 5 and 8 are more favorable; this is indicated by the increased formation of pentafulvene as a by-product. [11±15] With respect to the formation of fullerene-like moieties or building blocks, the effect of benzannelation on the barriers and enthalpies of formation is also important.…”

Section: Introductionmentioning

confidence: 89%

The Cyclization of Parent and Cyclic Hexa-1,3-dien-5-ynes—A Combined Theoretical and Experimental Study

et al. 2001

View full text Add to dashboard Cite

The thermal cycloisomerization of both parent and benzannelated hexa-1,3-dien-5-yne, as well as of carbocyclic 1,3-dien-5-ynes (ring size 7-14), was investigated by using pure density functional theory (DFT) of Becke, Lee, Yang, and Parr (BLYP) in connection with the 6-31G* basis set and the Brueckner doubles coupled-cluster approach [BCCD(T)] with the cc-pVDZ basis set for the parent system. The initial cyclization product is the allenic cyclohexa-1,2,4-triene (isobenzene), while the respective biradical is the transition structure for the enantiomerization of the two allenes. Two consecutive [1,2]-H shifts further transform isobenzene to benzene. For the benzannelated system, the energetics are quite similar and the reaction path is the same with one exception: the intermediate biradical is not a transition state but a minimum which is energetically below isonaphthalene. The cyclization of the carbocyclic 1,3-dien-5-ynes, which follows the same reaction path as the parent system, clearly depends on the ring size. Like the cyclic enediynes, the dienynes were found to cyclize to products with reduced ring strain. This is not possible for the 7- and 8-membered dienynes, as their cyclization products are also highly strained. For 9- to 11-membered carbocycles, all intermediates, transition states, and products lie energetically below the parent system; this indicates a reduced cyclization temperature. All other rings (12- to 14-membered) have higher barriers. Exploratory kinetic experiments on the recently prepared 10- to 14-membered 1,3-dien-5-ynes rings show this tendency, and 10- and 11-membered rings indeed cyclize at lower temperatures.

show abstract

Section: Introductionmentioning

confidence: 89%

The Cyclization of Parent and Cyclic Hexa-1,3-dien-5-ynes—A Combined Theoretical and Experimental Study

et al. 2001

View full text Add to dashboard Cite

show abstract

“…[10,11] The interactions with nucleophiles in positions 2 and 4 have been interpreted as a manifestation of polar character in 2, corresponding to the electron distribution of 2b. [15] 3δ 2 -Chromene (11) should even be more polar, since the dipole 11b can take advantage of the aromatic stabilisation of the benzopyrylium ion (Scheme 5). The high yield (79%) of the acetal formed in the reaction between KOtBu and 11, in which position 2 is attacked exclusively, is in line with this assumption.…”

Section: Methodsmentioning

confidence: 99%

“…However, if furan or styrene is present, 11 preferentially undergoes a cycloaddition. [15] An experimental and theoretical study of 2-chloro-3δ 2 -chromene (12) (Scheme 5) has recently been published. [3] This species was observed directly in a matrix at 35 K and gave the 2-chlorobenzopyrylium ion on reaction with hydrogen chloride, which is in agreement with the properties of the dipole 12b.…”

Section: Methodsmentioning

confidence: 99%

See 1 more Smart Citation

1-Methyl-1-azacyclohexa-2,3-diene(N−B)borane − Generation and Interception of an Unsymmetrical Isodihydropyridine

et al. 2001

Self Cite

View full text Add to dashboard Cite

Keywords: Allenes / Amines / Boranes / Cycloadditions / Eliminations / Strained molecules 3-Bromo-1-methyl-1,2,5,6-tetrahydropyridine(N−B)borane (7) was prepared from 3-bromopyridine by conversion to 3-bromo-1-methylpyridinium iodide, hydrogenation of the latter with sodium tetrahydroborate and treatment of the resulting 3-bromo-1-methyl-1,2,5,6-tetrahydropyridine (6) with borane−dimethyl sulfide. Whereas no trapping product of the possible intermediate 1-methyl-1-azacyclohexa-2,3-diene (4) could be observed on treatment of 6 with potassium tert-but-

show abstract

“…[10] [a] Treatment of a solution of 3 in furan or 2,5-dimethylfuran with KOtBu afforded the tetrahydroepoxynaphthalenes 4 and 5, respectively.…”

mentioning

confidence: 99%

Cyclohexa-1,2,4-triene from 1-Bromocyclohexa-1,4-diene

Christl¹,

Groetsch

2000

Eur. J. Org. Chem.

Self Cite

View full text Add to dashboard Cite

1‐Bromocyclohexa‐1,4‐diene (3) was prepared from trans‐4,5‐dibromocyclohexene by elimination of hydrogen bromide. Treatment of a solution of 3 in furan or 2,5‐dimethylfuran with KOtBu afforded the tetrahydroepoxynaphthalenes 4 and 5, respectively. The structure of these products is evidence for the title cycloallene (isobenzene 1) being the reactive intermediate. The compounds 4 and 5 were dehydrogenated by DDQ to the known dihydroepoxynaphthalenes 6 and 7, respectively. These conversions unambiguously confirm the structures of 4 and 5. In pure styrene, 3 was not attacked by KOtBu, and only upon the addition of 18‐crown‐6 did a reaction occur. This reaction did not, however, furnish the known [2+2] cycloadduct 9 of styrene and 1, but, instead, a small amount of 1,2‐diphenylethane (8) was formed. In agreement with this finding, the conjecture that 1 was deprotonated to give the phenyl anion was confirmed by the treatment of a solution of 3 and benzophenone in THF with KOtBu, which resulted in the formation of triphenylmethanol.

show abstract

3δ2-Chromene (2,3-Didehydro-2H-1-benzopyran): Generation and Interception

Cited by 23 publications

References 38 publications

The Cyclization of Parent and Cyclic Hexa-1,3-dien-5-ynes—A Combined Theoretical and Experimental Study

The Cyclization of Parent and Cyclic Hexa-1,3-dien-5-ynes—A Combined Theoretical and Experimental Study

1-Methyl-1-azacyclohexa-2,3-diene(N−B)borane − Generation and Interception of an Unsymmetrical Isodihydropyridine

Cyclohexa-1,2,4-triene from 1-Bromocyclohexa-1,4-diene

Contact Info

Product

Resources

About