Alkaloid-fullerene systems through photocycloaddition reactions

The photocycloaddition of tertiary amines to [60]fullerene (C-60) is an int eresting 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 tha t 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 phot ochemically to give two products, the expected [6,6] monoadduct (5a, 5b) an d a new type of monoadduct with a bis-[6, 6] closed structure (4a, 4b). The se 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 HMB C (heteronuclear multiple-bond connectivity) spectroscopy. The techniques o f 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 mi xture from photoaddition of la to C-60 containing a He-3 atom (He-3@C-60) l ed to two peaks at -9.091 and -11.090 ppm relative to gaseous He-3, consist ent with formation of a [6,6]-closed monoadduct and a bis-[6,6] closed addu ct. Presumably, the bis-[6, 6] closed adducts are formed by an intramolecul ar [2 + 2] cycloaddition of the vinyl group to the adjacent 6,6-ring juncti on of C-60 after the initial photocycloaddition.