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on their response to thermal excitation the azabarbaralanes described here are divisible into two distinct categories: the pair (7) and (8) readily rearranges at ambient temperature"' whereas (5)13, 6, '1 and ( 6 ) L 3 3 '1 effectively resist change even at elevated temperatures. The difference between the two classes is perhaps best exemplified by direct comparison between (7) whose half-life was found (NMR; [D6]-acetone) to be a mere 18 min (AG' ~2 2 kcal/mol) at 32°C and ( 5 ) which may be recovered unchanged (NMR) after being heated at 140°C for 30min! Since of the four 9-azabarbaralanes described here the two that are thermally unstable, uiz. (7) and ( 8 ) , are also the only members that incorporate lone pairs which are well accessible electronically for interaction with the homotropilidine moiety of the molecule, one must conclude that the nitrogen lone pair exerts a destabilizing effect on the 9-azabarbaralane system.

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Das aus α‐Chlormalonsäureesterchlorid (I) mit Et3N erzeugte Chlorketon (II) reagiert in situ mit Cyclopentadien zu dem Bicyclo‐ heptenon (III), dessen Dechlorierung mit Bu3SnH die epimeren Ketoester (IV) liefert.