The title compounds were obtained by a reaction sequence starting from diphenylmethyl 4,5-0-isopropylidenequina$e. Suitably protected cinnamyl chlorides were condensed with this compound, followed by reaction of the intermediate esters with hydrazine hydrate, and then with acetic acid-formic acid-water. The total yields of 3-0-o. As already mentioned in the foregoing paper ( 5 ) . the synthesis of the title compounds by the method proposed by HASLAM et a2 for the synthesis of e.g.
3-O-p.coumaryl-D-(-)-quinicacid (1x)(6), gave rather disheartening results. In fact, the final removal of the protective functions from the easily prepared intermediates (e.g. V I ) required prolonged acidic treatment, entailing heavy losses of material. However, a s this requirement could be explained by the high stability of the employed 1-0-ethoxycarbonyl-protection (as in VI) in acidic medium, it seemed worthwhile to investigate a synthetic procedure based on the use of diphenylmethyl 4,5-0-isopropylidenequinate (II), a compound without any protection on the 1-hydroxyl-function. This approach looked promising, because in I1 a marked difference towards acid chlorides between the sterically hindered, axial tert. alcohol group on C-1 and the equatorial sec. alcohol group on C-3 may be expected (see e.g. ( 7 -1 0 ) ) .The results obtained confirm the validity of this supposition. The procedure, followed for the synthesis of the title compounds VIII, XI and XI1 is depicted in the scheme.-663 -
The experimental circumstances for the synthesis of 3‐O‐acyl‐D‐(‐)‐quinic acids by the procedure of Haslam et al are improved, and applied to the preparation of the title compounds. The substances are obtained in overall yields of respectively 36%, 25% and 20%, comparing favourably with the reported results of respectively 8%, 7% and 6.5%.
Durch Kondensation des aus dem Hydroxyketon (I) und Diphenyldiazomethan erhältlichen Esters (II) mit den Säurechloriden (III) zu den (nicht isolierten) Estern (IV), Abspaltung der Phenolschutzgruppen mit Hydrazinhydrat und saure Hydrolyse wurden die am 3‐O acylierten Chinasäuren (V) dargestellt.
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