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

Abstract

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.

Formation of Polycyclic Aromatic Hydrocarbons and Nitrogen Containing Polcyclic Aromatic Compounds in Titan's Atmosphere, the Interstellar Medium and Combustion

“…This addition occurs without a barrier and is 43.1 kcal mol -1 exothermic (see Figure 12). Again, the finding that the CN addition to the aromatic ring in styrene is barrierless is in line with the previous experimental and theoretical studies of the reaction of cyano radicals with benzene 54,59,53 and toluene. 59 Once the adduct i10 forms, it may lose the H atom from the attacked ortho carbon yielding 2-vinylbenzonitrile.…”

“…In our previous work, 54 Although the creation of the naphthalene core could now be achieved without any problems, we still had failed to make naphthalene itself. Our best attempts, up to now, had been producing substituted naphthalene or azanaphthalene molecules.…”

Theoretical study of omeprazole behavior: Racemization barrier and decomposition reaction

“…In this article, racemization barriers are obtained by quantum chemistry calculations. In this sense, there are some articles which use quantum chemistry for calculating racemization barriers of helicenes 14, chiral biphenyl 15, sulfoxides 16, among others 17–19. In the Allenmark and Oxelbark work 16, a planar intermediate was established as the transition state for suphoxides, and the racemization barrier was calculated from the difference between ground and transition states for pyramidal inversion.…”

Stable Five‐Membered‐Ring Allenes with Second‐Row Elements Only: Not Allenes, But Zwitterions

“…The barrier to enantiomerization of 1,2,4-cyclohexatriene (3 a) amounts to approximately 10 kcal mol À1 . [5][6][7] At variance with 3 a, the transition state of this process, that is the diradical 3 b, proved to be an achiral species, whose atoms, except for the hydrogen atoms at C6, lie in one plane.…”