Chameleonic Reactivity of Vicinal Diazonium Salt of Acetylenyl-9,10-anthraquinones: Synthetic Application toward Two Heterocyclic Targets

Chameleonic Reactivity of Vicinal Diazonium Salt of Acetylenyl-9,10-anthraquinones: Synthetic Application toward Two Heterocyclic Targets Full article

Journal

Journal of Organic Chemistry
ISSN: 0022-3263

Output data

Year: 2011, Volume: 76, Number: 21, Pages: 8737-8748 Pages count : DOI: 10.1021/jo2014214

Authors

Stepanov A. A. ¹ , Gornostaev L. M. ³ , Vasilevsky S. F. ¹ , Arnold E. V. ³ , Mamatyuk V. I. ² , Fadeev D. S. ² , Gold B. ⁴ , Alabugin I. V. ⁴

Affiliations

1	(Данные Web of science) Russian Acad Sci, Inst Chem Kinet & Combust, Siberian Branch, Novosibirsk 630090, Russia
2	(Данные Web of science) Russian Acad Sci, NN Vorozhtsov Novosibirsk Inst Organ Chem, Novosibirsk 630090, Russia
3	(Данные Web of science) Krasnoyarsk State Pedag Univ, Dept Chem, Krasnoyarsk 660049, Russia
4	(Данные Web of science) Florida State Univ, Dept Chem & Biochem, Tallahassee, FL 32306 USA

The nature of products in the diazotization of 1-amino-2-acetylenyl-9,10-anthraquinones strongly depends on the nature of substituents at both the alkyne and at the anthraquinone core. Donor substitution (NHAr, OH) at the fourth position stabilizes the diazonium salt at Cl, decelerating electrophilic cyclization at the arylethynyl substituent at C2. This effect allows the replacement of the diazonium with azide group and subsequent closure into isoxazole ring with preservation of the alkyne. In contrast, electrophilic 5-exo-dig cyclizations to condensed pyrazoles is observed for the combination of donor substituents at the aryl alkyne moiety and an OAc substituent at C4. The latter process provides a new synthetic route to 3-ethynyl[1,9-cd]isoxazol-6-ones that are difficult to access otherwise. DFT calculations suggest that donor substituents have only a minor effect on alkyne and diazonium polarization in the reactant but provide specific transition state stabilization by stabilizing the incipient vinyl cation. This analysis provides the first computational data on electrophilic 5-exo-dig cyclization in its parent form and the nucleophile-promoted version. This cyclization is a relatively fast but endothermic process that is rendered thermodynamically feasible by the enol-keto tautomerization with concomitant aromatization in the five-membered heteroaromatic ring. Computations suggest that the importance of nucleophilic assistance in the transition state for a relatively weak nucleophile such as water is minor because the energy gain due to the Lewis base coordination to the carbocationic center is more than compensated for by the unfavorable entropic term for the bimolecular proces.

Stepanov A.A. , Gornostaev L.M. , Vasilevsky S.F. , Arnold E.V. , Mamatyuk V.I. , Fadeev D.S. , Gold B. , Alabugin I.V.
Chameleonic Reactivity of Vicinal Diazonium Salt of Acetylenyl-9,10-anthraquinones: Synthetic Application toward Two Heterocyclic Targets
Journal of Organic Chemistry. 2011. V.76. N21. P.8737-8748. DOI: 10.1021/jo2014214 WOS Scopus РИНЦ

Published print:

Nov 4, 2011

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