Читать книгу Recent Advances in Polyphenol Research - Группа авторов - Страница 37

Selenski and Pettus (2006) developed an efficient synthetic approach to bicycle 45, corresponding to the aglycon of diinsininol (46), by exploiting the [3+3] annulation approach (Figure 2.21). As an electrophilic unit, flavylium 40 was prepared by the condensation of 2,4,6‐triacetoxybenzaldehyde (38) and 3,4‐dihydroxyacetophenone (39). On the other hand, the nucleophilic partner 44 was synthesized from styrene 41 and benzaldehyde 42. Treatment of 42 with LiAlH₄ in the presence of MgBr₂ generated o‐quinonemethide A, which underwent a [4+2]‐cycloaddition with styrene 41, giving the corresponding flavan 43 in 45% yield. DDQ‐oxidation in the presence of H₂O followed by removal of the protecting groups afforded free flavanone 44 in 72% yield (two steps). The reaction of flavylium salt 40 with nucleophile 44 (6 equiv) proceeded under microwave irradiation at 120 °C, giving the annulated product 45 in 32% yield. The product was obtained as a single diastereomer, albeit in a racemic form.