Abstract
Treatment of alloxan-5-oximes with different types of phosphonate carbanions gave moderate to high yields of condensed and spiro bis-heterocyclic systems bearing a phosphonate substituent. Mechanisms for the formation of the five- and six-membered rings were provided. A marked resemblance between alloxan-5-oxime and 1,3-dimethyl derivative is observed through the studied reactions. The bioassay indicated that some of the products have good selective anti- tumor activity and the structure-activity relationship (SAR) of new phosphonates has also been studied.
Highlights
A novel heterocyclic transformation reaction has been described involving an additionelimination, and rearrangement sequence of violuric acid (1) with saturated, unsaturated and active alkylidenephosphoranes leading to a series of oxazolo-pyrimidenes as well as pyrimidooxazines (Scheme 1).1 It has been pointed out that the reactions of such ylides proceeded only when the latter were generated in situ from the corresponding salts in the presence of ~3-fold excess LiOH
The findings reflected the inertness of molecule 1, which was attributed to the low reactivity of the oxime function and the amidic carbonyl group toward nucleophilic attack
An ethanol solution of 1.5 equivalent of the phosphorus reagent was treated with a solution of sodium ethanolate (EtONa, 4.5 equiv.) to generate the carbanion, and the oxime substrate was added
Summary
A novel heterocyclic transformation reaction has been described involving an additionelimination, and rearrangement sequence of violuric acid (1) with saturated, unsaturated and active alkylidenephosphoranes leading to a series of oxazolo-pyrimidenes as well as pyrimidooxazines (Scheme 1).1 It has been pointed out that the reactions of such ylides proceeded only when the latter were generated in situ from the corresponding salts (see Scheme 1) in the presence of ~3-fold excess LiOH (aqueous). Compound 5a (δp = 24.3 ppm) showed in its 1H NMR spectrum (d6-DMSO) the ethyl group of the phosphonate ester at δ 0.98, 1.21 (2dt, JHH = 6.5, JPH = 3.8 Hz, 2 × 3H, 2 × H3C.C.O), and at δ 3.75-3.89 (2dq (m), 4H, 2 × H2CO).
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