RESUMEN
Methyl (α-naphthyl) acrylates bearing an ortho-substituent with a hydrogen atom produce naphthocyclobutenes upon Ir(Fppy)3-mediated photosensitization. This reaction can be described as a carbon analogue of the Norrish-Yang reaction: upon triplet excitation of the acrylate a 1,5-HAT results in a 1,4-diradical which forms the cyclobutene. Diastereoselectivities up to >20:1 were observed for the ring-closure reaction.
RESUMEN
Disclosed herein is a visible light mediated cyclization of methyl (α-naphthyl) acrylates and heteroaromatic analogues yielding substituted acenaphthenes and azaacenaphthenes. This highly functional-group-tolerant transformation was put to the test in an enantioselective formal synthesis of delavatine A. Mechanistic details were elucidated by DFT-calculations revealing an unusual intramolecular H-transfer mediated by a primary amine. The generality of this transformation enables a novel synthetic strategy of five membered ring annulation at an advanced stage, allowing reliance upon naphthalene chemistry up to the point of acenaphthene construction.
RESUMEN
The alkaloid (-)-tylophorine was isolated from a sample of Tylophora indica, and the crude extract was analyzed by HPLC/MS(n) and chiral HPLC/MS. While the literature states that the naturally occurring form of this alkaloid is the R-enantiomer and that its S-antipode is usually not found in nature, we confirmed the hypothesis of Govindachari and Nagarajan that natural levorotatory tylophorine is indeed a nearly racemic mixture with a slight excess of the R-enantiomer.