Wiley InterScience Backfile Collection 1832-2000
Chemistry and Pharmacology
2-Substituted 1,6-Methanoannulenes as Dienophiles in the [4 + 2]Cycloaddition with Inverse Electron DemandThe LUMO-diene-controlled [4 + 2] cyclo-additions of various at C-2 substituted 1,6-methano annulenes 6, 10 and 13 with the electron-deficient s-cis-fixed diazadiene system of 3,6-bis(trifluoromethyl)-1,2,4,5-tetrazine (3) are described. With the donor substituted 6 (or its valence tautomer 7) 3 reacts under unusually mild conditions to give the 7,12-methanocyclodeca[d]pyridazine 9 with high site selectivity. The Diels-Alder reaction of 3 with the 2-bromo-1,6-methanoannulene (10⇌11) leads to the 6- and 8-bromo-7,12-methanocyclodeca[d]pyridazines 12a and 12b, whereas with the various acceptor substituted species 13⇌14 the 8-substituted 7,12-methanocyclodeca[d]pyridazines 15a-c are formed exclusively. Spectroscopic data show, that for all the novel methanocyclodeca[d]pyridazines 9, 12 and 15 the annulenic structure is dominating, but a remarkable reduction of the ring current and a distinct bond alternation is observed compared to the parent 1,6-methanoannulene 1.
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