Diels–Alder reaction of 2,7‐dichloroquinoline‐5,8‐dione with a thiazole o‐quinodimethane. Assignment of the regiochemistry by ¹H–¹³C HMBC correlations

Abstract

The Diels-Alder reaction between a thiazole o-quinodimethane and 4,6-dichloroquinoline-5,8-dione gave 6-chloro-9-azaanthra[2,3-b]thiazole-5,10-dione as a single regioisomer. Its structure was assigned by 2D 1 H-13 C HMBC short-and long-range correlations. Measuring the spectra in CF 3 CO 2 D indicated that both nitrogen atoms of pyridine and thiazole rings are deuterated.

Very Long-Range Correlations (nJC,H n > 3) in HMBC Spectra

“…The modification of Δ 2 from 65 ms ( n J C,H = 7.7 Hz ) to 100 ms ( n J C,H = 5 Hz) was not sufficient to show any differences in the observed correlations (Figure 2a). Correlations across five-bond have been observed also for heterocyclic quinones [22]. In an HMBC experiment carried out in CF 3 CO 2 D at 500.13 and 125.78 MHz for 1 H and 13 C, respectively, with Δ 2 = 80 ms, several 4 J C,H and two 5 J C,H correlations were observed (Figure 2b).…”

“…The HMBC of ethyl chrotonate, a structurally simple compound, also shows a five-bond correlation in its HMBC spectrum, in CDCl 3 solution, (Δ 2 = 65ms), through a coupling path with a high degree of conformational freedom [22] (Figure 3a). With the same Δ 2 , the HMBC spectra of (E) and (Z) 3-(4-oxo-4H-chromen-3-yl)-acrylic acid ethyl esters, compounds bearing the acrylate moiety, do not show these long-range correlations, although some 4 J C,H correlations were observed.…”

“…For example, there has been reported the use of Δ 2 values from 50 to 400 ms to record HMBC spectra of phenolic compounds [19]. Also, the observation of five-bond correlations by using a standard value of Δ 2 (65 or 80 ms) in HMBC spectra has been reported [20][21][22]. Similarly, several examples of 4 J CH have been observed in a great variety of molecules, and coupling pathways [9].…”

Long-range correlations ( n j C,H n > 3 ) in the HMBC spectra of 3-(4-oxo-4H-chromen-3-YL)-acrylic acid ethyl esters

“…For example values of ∆ 2 between 50 to 400 ms to record HMBC spectra of phenolic compounds, has been reported, 20 moreover the observation of five bonds correlations by using standard value of ∆ 2 (65 or 80 ms) in HMBC spectra of quinones has also been reported. 12,13,21 In a similar way, several examples of 4 J CH has been observed in a great variety of molecules and coupling pathways. 10 Generally the choice of ∆ 2 is made on arbitrary basis rather than from knowledge of the actual value of the couplings.…”

Cascade synthesis of 2-amino-5-(4-methoxyphenyl)-4-phenyl-1,3-thiazole by reaction of 4-chloro-N-[2,2-dichloro-1-(4-methoxyphenyl)-2-phenylethyl]benzenesulfonamide with thiourea

“…The carbon atom linked to the phenyl group resonated in a weaker field as compared to that connected to the p-methoxyphenyl group (δ C 144.07 and 119.08 ppm, respectively). As a rule, thiazole systems are characterized by downfield signal of C 4 due to stronger deshielding effect of the ring nitrogen atom [15,16].…”