The practicality of constructing highly condensed alicyclic frameworks through multiple Diels-Alder cycloaddition reactions (of the domino or pincer type) involving 9,10-dihydrofulvalene, decachloro-9,1O-dihydrofulvalene, and 1 I , 12-dihydrosesquifulvalene is presented in full detail. Illustrative of the synthetic potential of the method are efficient syntheses of hexahydro-3,4,7-methenocyclopenta[a]pentalene (lo), octahydro-3,6-dimethylenedicyclopenta[cd,g~]pentalene ( l l ) , triquinacene (12), and a number of previously unknown (CH)12 isomers. The greatly enhanced 4~ donor reactivity of cyclopentadiene relative to cycloheptatriene rings does not permit the isolation of intermediate stage adducts in those instances where only fivemembered cycles are involved. When the larger rings are present, temperatures in excess of 130 OC are required to complete the overall formation of four new (T bonds. Decachloro-9,10-dihydrofulvalene exhibits greatly reduced reactivity relative to its hydrocarbon analogue and consequently is of limited practical utility. The varied responses of four somewhat related polycyclic azo compounds (37,48,49, and 63) to thermal and photochemical activation are also demonstrated.Those structural features unique to the [2.2]-and [3.3]-paracyclophanes rather tightly compress transannularly disposed .rr networks and beget a modicum of interaction between them.4 Of particular relevance to the present investigation are those two-stage cycloadditions which lead to polycyclic products. There are formally two ways in which such multistage C-C bond forming reactions can occur. Illustrative of the first type are the efficient condensation of [2.2](2,5)furanophane(1) with tetrachlorocyclopropene to give 2,s the reaction of anti-[2.2]naphthalenophane (3) with singlet oxygen in methanol to provide 4,6 and the capture of dimethyl acetylenedicarboxylate by anthracenophane 5.' Here initial intermolecular cycloaddition of a dienophile to a 1,3-diene part structure generates a new olefinic center which subsequently becomes directly involved as a dienophile in a n ensuing intramolecular (rd + x2) bonding scheme.8 W e shall hereafter refer to such multiple cycloaddition processes as "domino Diels-Alder" reaction^.^ 2 -1 -* CH300C-Czc-COOCH~ &/ . & COOCH3 6 COOCH3 s The second cyclocondensation pathway requires that the dienophile be originally acetylenic and proceeds by utilization of both degrees of unsaturation in the triple bond to achieve two-stage cyclization. The reactivity of 1Io and naphthalenofuranophane SI1 toward dimethyl acetylenedicarboxylate serves as prototypical examples. Their classification as "pincer Diels-Alder reactions" would seem appropriate since this term clearly connotes that compression of a dienophile between two diene components has transpired. Either process is seen to lend itself readily to the formation of four new C-C bonds and to the construction of a rather elaborate polycyclic structure in a single laboratory manipulation. Clearly, if less sterically compressed polyolefins were...

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