No abstract

Treatment of sodium N-(o-azidobenzoyl)aminoacylglycinates 8 with acetic anhydride afforded 1-acetyl-4-(o-azidobenzoyl)-2,5-piperazinediones 7, with complete retention of the stereochemistry. The intramolecular aza Wittig reactions of compounds 7 in the presence of tributylphosphine followed by deacetylation gave 1,2-unsubstituted pyrazino[2,1-b]quinazoline-3,6-diones 1. This route was adapted to the synthesis of both enantiomers of the alkaloid glyantrypine.

Microwave-Assisted Synthesis of 2,5-Piperazinediones under Solvent-Free Conditions. -The microwave-promoted cyclocondensation of N-Boc protected dipeptide esters is described as an efficient method for the synthesis of polysubstituted 2,5-piperazinediones. -(LOPEZ-COBENAS, A.; CLEDERA, P.; SANCHEZ, J. D.; LOPEZ-ALVARADO, P.; RAMOS, M. T.; AVENDANO, C.; MENENDEZ*, J. C.; Synthesis 2005, 19, 3412-3422; Dep. Quim. Org. Farm., Fac. Farm., Univ. Complutense, E-28040 Madrid, Spain; Eng.) -Mais 18-186

Microwave irradiation leads to a considerable improvement of the cyclocondensation between anthranilic acid and lactim ethers derived from piperazine-2,5-diones in terms of reaction times, yields, and stereocenter integrity. This reaction has been used to prepare some derivatives of the pyrazino[2,1-b]quinazoline-3,6-dione system present in many quinazoline alkaloids. It could also be applied to the synthesis of compounds containing the complete hexacyclic ring system of the anti-MDR natural product N-acetylardeemin, and other comprising the pentacyclic framework of circumdatin E. The microwave-assisted reaction was also much better than the thermal one when applied to a bis-lactim ether, leading to the corresponding pentacyclic pyrazino[2,1-b:5,4-b¢]diquinazoline-8,16-dione in excellent yield.

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