Flash vacuum pyrolysis (FVP) has been used successfully to discover some novel thermal reactions. These provide new insights into some fundamental chemistry;In part I, benzocyclobutene (9) and its 4+4 dimer, 1,5-dibenzocyclooctadiene (14) were found to give anthracene (7) as a major product. The similarity of the product mixtures is taken as evidence that essentially the same mechanism is operating in both cases. By labeling studies, the 4+2 spirodimer (14') appears to be an intermediate. The fragmentation by which 14' is thought to give 7 is new and analogous to the retroene reaction. The proposed mechanism lends new insight into the mechanism of the pyrolytic formation of benzene and higher aromatics;In part II, vinylketene (66), prepared by FVP, was characterized by low-temperature ('1)H- and ('13)C-NMR spectroscopy. It was found to dimerize by a novel 4+2 cyclo-addition reaction. The resulting (delta)-lactone (90) was isomerized to a mixture of sibirinone (91) and 6-allyl-(alpha)-pyrone (92). Acid-catalyzed isomerization gave primarily 91 (9:1 mole ratio). When vinylketene was mixed with cyclopentadiene, the 2+2 cycloadduct (72) was formed with high regio- and stereospecificity. Compound 72 was isomerized to bicyclo4.2.1nona-3,7-dien-2-one (97);Part III described an attempt to determine the effect of surface catalysis in FVP. The synthesis of 5,8-diphenyltetralin (9) was described. Comparison of the pyrolysis of 9 to that of the parent compound, tetralin (1) was not possible since the thermal chemistry of 9 was found to be too different from that of 1. The major product of the pyrolysis of 9 at 1000(DEGREES)C and 10('-5) torr was due to the loss of;C(,2)H(,6) while 1 gave styrene as the major product by the loss of C(,2)H(,4) under similar conditions; *DOE Report IS-T-1111. This work was performed under contract No. W-7405-Eng-82 with the U.S. Department of Energy.