Alkaloid-fullerene systems through photocycloaddition reactions

The photocycloaddition of tertiary amines to [60]fullerene (C-60) is an interesting and useful reaction. We wished to extend the applications of this type of reaction through an investigation of the photoaddition of alkaloids to C-60 for the purpose of synthesizing novel and complex photoadducts that are difficult to obtain by usual methods. Irradiation of tazettine (2) or gramine (3) with Cao in toluene leads to formation of one monoadduct (6 or 7), whereas scandine (1a) or 10-hydroxyscandine (Ib) reacts with C-60 photochemically to give two products, the expected [6,6] monoadduct (5a, 5b) and a new type of monoadduct with a bis-[6, 6] closed structure (4a, 4b). These new structures were characterized by W-vis, FT-IR, H-1 NMR, C-13 NMR, H-1-H-1 COSY, ROESY, HMQC (heteronuclear multiple-quantum coherence), and HMBC (heteronuclear multiple-bond connectivity) spectroscopy. The techniques of time-of-flight secondary ion MS (TOF-SIMS) and field desorption MS (FD-MS) were used for the mass determination. He-3 NMR analysis of the product mixture from photoaddition of la to C-60 containing a He-3 atom (He-3@C-60) led to two peaks at -9.091 and -11.090 ppm relative to gaseous He-3, consistent with formation of a [6,6]-closed monoadduct and a bis-[6,6] closed adduct. Presumably, the bis-[6, 6] closed adducts are formed by an intramolecular [2 + 2] cycloaddition of the vinyl group to the adjacent 6,6-ring junction of C-60 after the initial photocycloaddition.