“…Thus 1 reacts with butadiene84 to give the dihydro [10]annulene 108 in addition to 109, the product of diradical trapping. It reacts with aryl nitrile oxides to yield the heterocyclic propellanes 110,96 with a-pyrone to give l,6-methano [10]annulene 111,84 with 1,2,4-triazines to afford the 3,8-methanoaza [10]annulenes 112 (several from reaction at high pressure),97 and with l,2,4,5-tetrazine-3,6-dicarboxylate to provide the diazotetraene 113.98 This last product84 has now been isolated and characterized as the bisnorcaradiene98 rather than its ring-opened valence bond isomer. Furthermore, bridged ten-electron [9]annulenes 114 and 116 emanate" from reaction of 1 with mesoionic oxathiazolines and dithiolanes, the latter via the isolable norcaradiene 115. The formation of compounds [111][112][113] proceeds by way of thermally labile cycloadducts that undergo decarboxylation or deazetation under the reaction conditions.…”