Ph. D. THESIS 2009
Ph. D. THESIS 2009
Ph. D. THESIS 2009
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Sch e m e 1 . Th e co n ve r sio n o f 1 in t o 2 via h y d r o ly sisd<br />
e ca r b o xy la tio n r o u t e .<br />
The reaction underwent with the complete hydrolysis and decarboxylation<br />
of all four ester groups. The total transformation is supported by TLC<br />
chromatography as well as by the melting point of the crude product, which is<br />
0.5°C smaller than that of the pure compound 2.We have to highlight the<br />
novelty of this method through its simplicity (one-step), high efficiency (yields<br />
over 96%) and because it requires no catalyst.<br />
We also developed an alternative way to the above proposed method. Thus,<br />
compound 1 was deposited on a solid support, placed into a teflon sealed tube<br />
and irradiated in microwave field.<br />
The results of these two methods can be summarized in Table 1:<br />
Table 1 Comparisson between classic and microwave irradiation methods<br />
Method Yield (%) M.p.<br />
7<br />
(ºC)<br />
classic Method (a) 98 250<br />
microwave<br />
irrad.<br />
Method (b) 90 249-250<br />
The advantages of these syntheses over the previous ones lie in the<br />
direct transformation of 1 into 2, as well as in the significantly increased yields,<br />
due to the absence of the acidic conditions and to the facile work-up procedure.<br />
1.3. Structural aspects in solution<br />
The bicyclic tetraester 1 and the bicyclic diketone 2 were both investigated<br />
by NMR spectroscopy in solution at room temperature in order to establish<br />
their structure and thereby to evidence the complete hydrolysis-decarboxylation<br />
of the precursor 1. This may present as most of β-ketoesters two tautomeric<br />
forms, enol and ketone, in equilibrium.<br />
Keto-enol tautomerization of compound 1 (Scheme 2) in CDCl3 solution<br />
has been investigated by NMR spectroscopy.