Furo(thieno)[3,2-d]pyrimidin-8-ones 1a,b and furo(thieno)[3,2-d]pyrimidine-8-thiones 7a,b have been synthesized
and their alkylation with a series of alkyl halides (MeI, EtI, PrI, i-PrI, BuI and BnCl) was carried out to gain
information on their lactam-lactim or thiolactam-thiolactim tautomerism and then on their different nucleophilicity. The
structure of the obtained compounds has been unambiguously confirmed by using a wide spectrum of physico-chemical methods as well as by
an alternative synthesis in some instances. Compounds 1a,b could be able to behave as ambident nucleophiles, in contrast compounds 7a,b
were able to behave ‘only’ as nucleophiles at sulphur: the obtained results confirmed the well known nucleophilicity sequence: S >> N > O.
Keywords: Furo(thieno)[3, 2-d]pyrimidin-8-one, furo(thieno)[3, 2-d]pyrimidine-8-thione, lactam-lactim and thiolactam-thiolactim tautomerism,
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