Synthesis, Thermal and Photochemical Reactivity of Highly Conjugated Arenediynes John D. Spence, Department of Chemistry, California State University Sacramento, 6000 J Street, Sacramento, CA 95819 Arylethynyl Enediynes: To examine the effect of extended conjugation on enediyne photoreactivity a series of arylethynyl arenediynes have been prepared. We have found that naphthalen-1-yl and phenanthren-9-yl substituents lead to a novel 2+2 photocyclization pathway while naphthalen-2-yl substituents require electron donating methoxy groups to afford C1-C6 Bergman cyclization products. A combined experimental and computational study is currently ongoing to further understand the role of the methoxy substituents. Aryl-Fused Quinoxalenediynes: We have discovered that extended benzannelation can alter the reactivity pathway of arenediynes. Upon heating in the presence of 1,4-cyclohexadiene, the parent 6,7-diethynylquinoxaline undergoes traditional C1-C6 Bergman cyclization followed by reduction to give 5,10-dihydrobenzoquinoxaline. In comparison, the corresponding phenylethynyl derivative affords a mixture of C1-C6 and C1-C5 cyclization products. We are currently examining aryl-fused quinoxalenediynes to determine if extended benzannelation can lead to C1-C5 cyclization as the predominant reaction pathway.