Corrigendum to “A multicomponent access to 1,3-thiazine-6-phenylimino-5-carboxylates” [Tetrahedron Lett. 57 (2016) 3256–3259] (S0040403916306670) (10.1016/j.tetlet.2016.06.007))

Article abstract of DOI:10.1016/j.tetlet.2018.07.018

In recent studies on the multicomponent route described in our original submission [1], we gained access to crystalline material suitable for X-ray analysis (Scheme 1). This revealed that our original structural assignment based on NMR, IR and MS evidence was incorrect. The product arising from the multicomponent reaction of ethyl 3-aminocrotonate (1), phenylisothiocyanate (2) and acetic anhydride (3) was not ethyl (Z)-2,4-dimethyl-6-(phenylimino)-6H-1,3-thiazine-5-carboxylate (5), but the thioamide isomer, ethyl 2,4-dimethyl-1-phenyl-6-thioxo-1,6-dihydropyrimidine-5-carboxylate (7) (Scheme 1 and insert). The structure of thioamide (7), and related analogues, is consistent with the NMR and IR data presented in our original submission. Using the compound numbering from the original manuscripts, analogues 8a–l, are the equivalent thioamides as shown in Table 1. Re-examination of the reaction mechanism based on this data supports a N to S anion resonance with the charge intercepted by acetic anhydride at the nitrogen anion stage [1,2]. As previously proposed, ensuing acetate loss and H-abstraction affords the ene-amine 9 which effects an intramolecular condensation with the N-acyl carbonyl moiety. Loss of water and acetate removal of the proton yields ethyl 2,4-dimethyl-1-phenyl-6-thioxo-1,6-dihydropyrimidine-5-carboxylate (Scheme 2). This mechanism differs only in the interception of the nitrogen anion rather than the sulfur anion by acetic anhydride, but this re-working is necessitated by the structure confirmed herein by X-ray crystallography. We regret any inconvenience this may have caused readers and sincerely apologize for this error.

Full text of DOI:10.1016/j.tetlet.2018.07.018

Tetrahedron Letters 59 (2018) 3155–3156
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Tetrahedron Letters
journal homepage: www.elsevier.com/locate/tetlet
Corrigendum
Corrigendum to ‘‘A multicomponent access to 1,3-thiazine-6-
phenylimino-5-carboxylates” [Tetrahedron Lett. 57 (2016) 3256–3259]
⇑
Trieu N. Trinh, Adam McCluskey
Chemistry, Centre for Chemical Biology, School of Environmental & Life Sciences, The University of Newcastle, University Drive, Callaghan, NSW 2308, Australia
In recent studies on the multicomponent route described in our
original submission [1], we gained access to crystalline material
suitable for X-ray analysis (Scheme 1). This revealed that our orig-
inal structural assignment based on NMR, IR and MS evidence was
incorrect. The product arising from the multicomponent reaction
of ethyl 3-aminocrotonate (1), phenylisothiocyanate (2) and acetic
anhydride (3) was not ethyl (Z)-2,4-dimethyl-6-(phenylimino)-
6H-1,3-thiazine-5-carboxylate (5), but the thioamide isomer,
ethyl 2,4-dimethyl-1-phenyl-6-thioxo-1,6-dihydropyrimidine-5-
carboxylate (7) (Scheme 1 and insert).
The structure of thioamide (7), and related analogues, is
consistent with the NMR and IR data presented in our original
submission. Using the compound numbering from the original
manuscripts, analogues 8a–l, are the equivalent thioamides as
shown in Table 1.
Table 1
Synthesis of substituted 1,3-thiazin-6-imino-5-carboxylates 8a–l.
Entry
1
R1
R2
Product
Yield (%)
65
CH3
8a
2
3
CH3
CH3
8b
8c
19
50
Re-examination of the reaction mechanism based on this data
supports a N to S anion resonance with the charge intercepted by
acetic anhydride at the nitrogen anion stage [1,2]. As previously
4
5
CH3
CH3
8d
8e
64
35
6
CH3
8f
20
7
8
CH3
CH3
8g
8h
29
29
9
CH3
8i
8j
15
29
10
CH3CH2
Scheme 1. Reagents and conditions: (i) rt, solvent free, N2, overnight; (ii) acetic
anhydride, CH3CN, rt, 24 h. Insert: ORTEP 3D view of 7 (30% ellipsoids shown).
11
12
8k
8l
4
CF3
12
DOI of original article: https://doi.org/10.1016/j.tetlet.2016.06.007
⇑
Corresponding author.
E-mail address: Adam.McCluskey@newcastle.edu.au (A. McCluskey).
https://doi.org/10.1016/j.tetlet.2018.07.018
0040-4039/Ó 2018 Elsevier Ltd. All rights reserved.

3156
T.N. Trinh, A. McCluskey / Tetrahedron Letters 59 (2018) 3155–3156
Scheme 2. Revised mechanism for the 3-component MCR reaction of 3-aminocrotonate, phenyl isothiocyanate (2) and acetic anhydride to give ethyl 2,4-dimethyl-1-phenyl-
6-thioxo-1,6-dihydropyrimidine-5-carboxylate (7), not ethyl (Z)-2,4-dimethyl-6-(phenylimino)-6H-1,3-thiazine-5-carboxylate (5).
proposed, ensuing acetate loss and H-abstraction affords the
ene-amine 9 which effects an intramolecular condensation with
the N-acyl carbonyl moiety. Loss of water and acetate removal of
the proton yields ethyl 2,4-dimethyl-1-phenyl-6-thioxo-1,6-dihy-
dropyrimidine-5-carboxylate (Scheme 2). This mechanism differs
only in the interception of the nitrogen anion rather than the sulfur
anion by acetic anhydride, but this re-working is necessitated by
the structure confirmed herein by X-ray crystallography.
We regret any inconvenience this may have caused readers and
sincerely apologize for this error.
References
[1] N.T. Trinh, A. McCluskey, Tetrahedron Lett. 56 (2016) 3256–3259.
[2] H.B. Jalani, J.C. Kaila, A.B. Baraiya, A.N. Pandya, V. Sudarsanam, K.K. Vasu,
Tetrahedron Lett. 51 (2010) 5686–5689.