Synthesis, structure, and photoisomerization of derivatives of 2-(2-quinolyl)-1,3-tropolones prepared by the condensation of 2-methylquinolines with 3,4,5,6-tetrachloro-1,2-benzoquinone

Synthesis, structure, and photoisomerization of derivatives

of 2-(2-quinolyl)-1,3-tropolones prepared by the condensation

of 2-methylquinolines with 3,4,5,6-tetrachloro-1,2-benzoquinone

Yury A. Sayapin a

, Bang Nghia Duong a

, Vitaly N. Komissarov a

, Igor V. Dorogan a

, Nadezhda I. Makarova a

,

Inna O. Bondareva a

, Valery V. Tkachev b

, Gennady V. Shilov b

, Sergey M. Aldoshin b

, Vladimir I. Minkin a,*

a Institute of Physical and Organic Chemistry, Southern Federal University, 194/2 Stachka St., 344090 Rostov on Don, Russian Federation

b Institute of Problems of Chemical Physics of Russian Academy of Sciences, 1 Akad. Semjonov N.N. Ave., 142432 Chernogolovka, Moscow region, Russian Federation

article info

Article history:

Received 31 May 2010

Received in revised form 4 August 2010

Accepted 31 August 2010

Available online 9 September 2010

Keywords:

1,3-Tropolones

Intermolecular hydrogen bond

Photolysis

Electrocyclic rearrangement

abstract

A series of novel derivatives of the 1,3-tropolone (b-tropolone) systemd2-(2-quinolyl)-5,6,7-trichloro￾1,3-tropolones and 2-(2-quinolyl)-4,5,6,7-tetrachloro-1,3-tropolones have been prepared by the acid￾catalyzed reaction of 2-methylquinolines with 3,4,5,6-tetrachloro-1,2-benzoquinone. The molecular

structures of two compounds, 2-(4-chloro-6,8-dimethyl-5-nitro-2-quinolyl)-5,6,7-trichloro-1,3-tropo￾lone 8 and 2-(4-chloro-7,8-dimethyl-5-nitro-2-quinolyl)-4,5,6,7-tetrachloro-1,3-tropolone 9, have been

determined using X-ray crystallography. According to the performed DFT B3LYP/6-311þþG** calculations

the tautomeric (OH) and (NH) forms of b-tropolones 8 and 9 are nearly energy equivalent, the latter

being more stabilized in polar media. Photolysis of 2-(2-quinolyl)-1,3-tropolones in heptane solution

leads to the disrotatory electrocyclic rearrangement resulting in the formation of a mixture of E- and

Z-isomers of 3-[2(1H)-quinolinylyden]-bicyclo[3.2.0]hept-6-en-2,4-dione derivatives.

2010 Elsevier Ltd. All rights reserved.

1. Introduction

It has been shown that the reaction of o-quinones with meth￾ylene active compounds serves as a convenient method for the

construction of 1,3-tropolone (b-tropolone) derivatives.1e5 The

mechanism of the reaction detailed by quantum chemical DFT

calculations5 involves, at its initial stage, formation of norcaradiene

derivatives, which subsequently isomerize to give b-tropolones. It

was reported1 that coupling 3,4,5,6-tetrachloro-1,2-benzoquinones

with acetone gives rise to the formation of an a-tropolone de￾rivative 1, but this conclusion was later called into question by the

results of a 2D NMR spectroscopic study2 of the structure of the

product, that attributed it to a b-tropolone derivative 2 (Fig. 1).

In this paper, we extend the previously studied acid-catalyzed

reaction3e5 of 2-methylquinolines with o-quinones to 3,4,5,6-tet￾rachloro-o-quinone derivative, describe a synthetic entry to novel

derivatives of 2-(2-quinolyl)-b-tropolones substituted in the seven￾membered ring and address the problem of the structure of the

tropolones obtained by this method.

To unambiguously assign the structure to a or b-isomeric form

X-ray determinations have been performed for two compounds

and the relative stability of the tautomeric forms of the tropolones

estimated by quantum chemical calculations using DFT B3LYP/6-

311þþG** method with account taken for solvation.

Recently, we have found that b-tropolones, similar to their a￾congeners6 are susceptible to a photoinduced electrocyclic rear￾rangement, occurring via the intramolecular OeH/N/O/HeN

excited state proton transfer followed by the disrotatory cyclization

of the seven-membered ring diene fragment.7 In the present work,

we attempted to apply this reaction to the newly obtained poly￾chloro-b-tropolones and studied photolysis of their hexane solu￾tions as well as absorption and fluorescence spectra of the initial

compounds and the products of the photochemical reaction.

Fig. 1. Structures of a-tropolone 1 and b-tropolone 2 derivatives.

* Corresponding author. Tel./fax: þ7 863 243 47 00; e-mail address: minkin@

ipoc.rsu.ru (V.I. Minkin).

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Tetrahedron

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2010 Elsevier Ltd. All rights reserved.

doi:10.1016/j.tet.2010.08.077

Tetrahedron 66 (2010) 8763e8771