65 according to the method of Huntress, Lesslie and Bernstein.

[B] The addition of thiazolo3to dimethyl acetylenedicarboxylate in dimethyIformamide.

The addition of 2,4-dialkyl and trialkylthiazoles to dimethyl acetylenedicarboxylate in dimethylformamide gave a class of

adducts formulated as the [3,4,0]-bicyclic structures, 8aH- thiazolo[ 3,2-a] pyridines, which could easily be separated by

chromatography from traces of accompanying yellow products. In the single case of 2-ethyl“4~methylthiazole, a low yield of a white isomer (60) was also isolated but the structure was not extensively investigated.

(a) Proton magnetic resonance

It was decided to make extensive use of proton magnetic resonance 3peut)rcGCopy in elucidation of structure since these compounds could be studied in their ground state. Any

perturbations or rearrangements which might occur when the molecule was in a higher energy state during reaction, would then be

avoided.

The proton magnetic resonance spectrum (Plate 1) of the structure (61) in deuterochloroform showed a group of signals (12H) at

S

38

with the findings of Acheson for the analogous SaH-

PIATE 1 3.71 - 3 .93 (61) 1.01 1.43 5 .7 0 3 .7 8 - 3 .8 9 (63) 0.91 8.68 3 .7 3 - 3 .8 8 (64)

y k

appeared at ^ 1.43 (CH^), a weakly resolved doublet (3H) at ^ 2.02 (CHg) and a broad unresolved line (1H) at ^ 5.70.

1.43 Me S. 5.08 1,58 2-02 MsA:--- (62)

The signals at S 2.02 arise from the protons of what was the 4-methyl group of 2,4-diînethylthiazole. There is slight

66 0

allylic coupling of the protons through four bçfnds

(J = 1.1 c./sec.) to the C-2 proton (what was the C~5 proton of 2,4~dimethylthiazole). The chemical shift of the protons of the methyl group at S 1.43 is in agreement with a value

of S 1'58 for the chemical shift of the 2-methyl protons in

the model compound 2,3-dimethyl-2,3-dihydrobenzothiazole (62). This methyl group must be on a tetrahedral carbon atom. These data suggest that cyclisation has taken place at the C-2

position of 2,4-dimethylthiazole.

The proton magnetic resonance spectra of the structures (63) and (64) from 2-ethyl-4-methylthiazole and 2,4,5-trimethyl thiazole were similar and in agreement with an analogous

structure. The signal arising from the methyl protons (3H) at 8 1,91 in compound (64) must be the methyl group adjacent

2 6 . 0.91 Me R 2.01 Me 5.68 ^ J ---- 1.98 Me R' 1.43 (63) (64)

to sulfur in agreement with a slight upfield shift relative to the methyl protons at S 1*98 adjacent to nitrogen in the

same compound. In the compound (63) the signals of the methylene protons are split into a quadruplet by the adjacent methyl

protons,as would be expected. The signals of the methyl protons

(3H) of the ethyl group appear as a triplet centred at S 0.91

and are further shielded by the methylene protons.

The addition of thiazole, monoalkyl and 2,5-dialkyl

thiazoles to dimethyl acetylenedicarboxylate in dimethylformamide gave what we consider to be members of another class of adducts containing the [5,2,0]-bicyclic structures, 8aH-azeto[1,2-^] [1,4]thiazepines (or the nine^membered ring 1,4-thiazonines). The major product was separated from traces of polar material by chromatography and, in the case of 2-alkylthiazoles, from

traces of an accompanying yellow product. 2-Kthylthiazole also gave a white isomer (65) having a similar proton magnetic resonance

spectrum to that of the isomer from 2-ethyl-4~metliylthiazole. The protoKii magnetic resonance spectrum (Plate 2) of the structure ( 66 ) in deuterochloroform showed a group of signals (12H) at f 3.72 - 3.92 (4C0gMe), two doublets of an AB system (2H)

(

)

27.

centred at S 6*02 and 6.52 (J » 4*75 c./sec.) and a singlet (IH) at 6 8.13. The lines of the AB system arise from the two

6.02 _e

(

)

adjacent protons on what was C-4 and C-5 of thiazole since

the coupling coaiBtant between these protons is in agreement with two vinylic protons on adjacent carbon atoms. The position of the signal (ÎH) at 6 8.13 requires the proton to be at what was C-2 of thiazole and thus be vinylic, since it does not agree with the chemical shift ( 6^5.08) of the proton on the tetrahedral

carbon atom in the model compound 2,3-dimethyl-2,3-dihydro- benzothiazole (62). The model compounds dimethyl-2-methylthio- phene-3,4-dicarboxylate (67), dimethyl ethylthiomethyXenemalonate

(68) and els and trans methyl-0-benzylthioacrylate (69) and (70) were prepared. The chemical shifts of the corresponding protons

(i.e. S 7.38 of the thiophene diester, §^8.34 of the thiomethylene*

7. 68

•rr

I

I

malonate and S 7.70 of the trans acryl&te) in these model

compounds are all in good agreement with the vinylic character of the isolated proton.

The proton magnetic resonance spectrum (Plate 2) of the structure ( 71) in deuterochloroform showed a group of signals

(12H) at ^ 3.72 - 3.90 (4C0 Me) a singlet (IH) at $ 8.07, a

weakly resolved doublet (3H) at & 2.12 (CH^) and a broad unresolved line (IH) at S 5.73 (vinylic).

8.07 5.73 ^

2.12

(71)

Tlie signals at §*2.12 arise from the protons of what was the 4~methyl group of 4-methylthiasole. These protons show allylic coupling (J = 1.3 c./sec.) with the vinylic proton through four bonds. The proton resonance at SS.07 requires

the proton to be vinylic in good agreement with the corresponding proton in structure ( 60 ). The signals of the vinylic protons are slightly upfield compared to those of the corresponding protons in structure ( 66 ) due to the shielding effect of the methyl protons ( S 2.12).

The proton magnetic resonance spectrum (Plate S) of the structure (72) in deuterochloroform showed a group of signals (12H) atSs.72 - 3.88 (4CXJ„Me), a singlet <3H) at _/S

S

PLATE 3.80 (72) l.fT 8.08 3.79 (73) (74) A

and two doublets of an AB system (2H) centred at 6 6*05 and $ 8.74 (J » 5.0 c./sec.)* The lines of the AB system are in the

2,67

Me 6.06

6.74

(72)

same region as those in structure (©.6 ) and, by similar

reasoning,correspond to the two adjacent protons on what was

C-4 and C-5 of 2-methylthiazole. The signal at

S

from 3 protons having a chemical shift in close agreement with