New Dienophiles: 1-Acetylvinyl Arenecarboxylates. Reactivity toward cyclopentadiene and exocyclic dienes (original) (raw)

1981, Helvetica Chimica Acta

The preparations of 1-acetylvinyl arenecarboxylates H2C=C (COCH,)OCOR with R = phenyl, p-nitrophenyl, 2,4-dinitrophenyl, u-and P-naphthyl are described (3). The Diels-A Ider reactivity of these dienophiles toward cyclopentadiene is evaluated and compared with that of methyl vinylketone, 3-trimethylsilyloxy-, 3-ethoxy-and 3-acetoxy-3-buten-2-ones. The stereoselectivity of the cycloadditions of these dienophiles with 2,3,5,6-tetramethylidene-7-oxanorbornane (1) and 5,sdimethoxy-l,4-epoxy-2,3-dimethylidene-I, 2,3,4-tetrahydroanthracene (2) is studied. In principle, the dienophiles 3 allow direct functionalization of the position C(9) of the A-ring of daunomycinone analogs by Diels-Alder additions to exocyclic dienes such as 1 and 2. Introduction.-Anthracyclinones are aglycones of very important antibiotics and anti-tumor drugs [l]. They can be prepared readily [2] [3] by two successive 3a-i R' 1 2a R1=R2=OCH3 R = a Me3Si f 2,4-(NO2)2-C6H3CO h RI=R2=H b Et g a-naphthyl-CO c R1=OCH3, R2=H c CH3CO h 8-naphthyl-CO d C~H S C O i CH3 e 4-(N02)-C6HdCO j H Diels-Alder additions [4] to 2,3,5,6-tetramethylidene-7-oxanorbornane (1) [5]. The A-ring of daunomycinone (4) [6] bears a hydroxy group at C(9), adjacent to the carbonyl function of the side-chain. This OH group can be introduced, in principle I)