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So far, “proton sponges” have been defined as bis(dialkylamino)arenes whose dialkylamino groups are in close spatial proximity.[1] The unusual basicity of these compounds is ascribed to the destabilizing overlap of the lone electron pairs on the nitrogen atoms, to the formation of especially strong hydrogen bonds in the monoprotonated diamines, and to the hydrophobic shielding of these hydrogen bonds. In order to differentiate and assess the relative importance of these factors, we were interested in quino[7,8‐h]quinoline 1, whose nitrogen atoms exhibit a mutual orientation similar to that in 1,8‐bis(dimethylamino)naphthalene 2 (“proton sponge”). In contrast to 2, however, 1 lacks the hydrophobic shielding of the hydrogen bonds of its monoprotonated derivative. This shielding is considered to be responsible for the low rates of proton transfer, which make the “proton sponges” reported so far unsuitable as auxiliary bases in chemical reactions.

Derivatization of 5 with carbon dioxide, dimethyl disulfide, and chlorotrimethylsilane leads to formation of the expected products 8 (50%), 9a (53%), and 9b (67%), respectively, which were characterized by NMR spectroscopy and mass spectrometry ( Table 1); dimethyl sulfate affords 2-methyl-1-pentene in 68% yield. Since the two anionic centers of 5 differ in their reactivity, the reaction can also be carried out stepwise with two different electrophiles, for example, first with one equivalent of dimethyl disulfide and then with chlorotrimethylsilane. The formation of 10 (Scheme l, Table l ) in 25% yield proves that-as expected-the homoallyl position is more reactive than the vinyl position. This is further supported by the tandem reaction with methanol and chlorotrimethylsilane, which gives mainly 2-trimethyl~ilyl-l-butene['~ (33%). However, the presence of traces of 2-lithio-1-butene 11 always has to be taken into consideration, since still unreacted 3 is in part metalated by 5.that, before ring-opening occurs to give 16, the initially formed radical anion 14 reacts with a second lithium atom to give the I-lithiomethylcyclopropyllithium 15. As a cyclopropylcarbinyllithium derivative, 15 then undergoes the known['"] anionic rearrangement with ring-opening to form the primary homoallyllithium derivative 17.['11 Experimental ProcedureApproximately 10% of a solution of 3 (8.0 g, 0.15 mol) I121 in 50 mL of die-thy1 ether was added dropwise, initially at room temperature, to a suspension of lithium powder (2.5 g, 0.36 mol, 2% sodium) in 50 mL of diethyl ether, the reaction being carried out under argon. After the reaction had begun-the reaction solution turned yellow and began to reflux-the remaining solution of 3 was added at ice-bath temperature so as to avoid partial evaporation of 3 (b.p. 10°C). The reaction mixture was then stirred for 1/2 h at room temperature and the excess lithium was filtered off under inert gas. Yield: 70-75% 5 ; very stable (half-life period of decomposition, 27 d at room temperature).

= 278, 248 nm)I7l und Dimethylbiphenylen (1 ,5-/I ,8-Gemisch, A,,, = 357, 254 nm) menbare Rotverschiebungen

Nahezu planar sind die beiden Titelverbindungen 1 und 2 im Kristall. Durch Röntgenstrukturanalyse beider Verbindungen konnten über Jahrzehnte bestehende Unsicherheiten bezüglich Synthese und Strukturzuordnung ausgeräumt werden. Bei der extrem starken und auch kinetisch aktiven Base 1 fällt der große zentrale äußere Winkel der Naphthalineinheit auf (125.4°), der einen relativ großen N ⃛N‐Abstand (272.8 pm) ermöglicht.

Trotz nahezu gleicher N ⃛N‐Abstände in 1 und 2 (272.8 bzw. 270.5 pm) ist die Basizitätskonstante von 2 um fast zwei Zehnerpotenzen geringer als die von 1. Ursache dürfte die helicale Struktur von 2 sein, die für die freie Base die destabilisierende „lone‐pair”︁‐Wechselwirkung der N‐Atome nahezu aufhebt und für 2a eine N ⃛H ⃛N‐Brücke entlang der Vorzugsrichtungen der „lone pairs”︁ der N‐Atome verhindert.

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