Cage expansion

In the reactions of 10.13a with alkali metal terr-butoxides cage expansion occurs to give the sixteen-atom cluster 10.15, in which two molecules of MO Bu (M = Na, K) are inserted into the dimeric structure. The cluster 10.13a also undergoes transmetallation reactions with coinage metals. For example, the reactions with silver(I) or copper(I) halides produces complexes in which three of the ions are replaced by Ag" or Cu" ions and a molecule of lithium halide is incorporated in the cluster. ... 

Scheme 9 Proposed cage expansion reactions leading to a ferrapentacarbaborane. Reproduced by permission of the American Chemical Society from Organometallics 1995, 14, 4463.

This doso-silaborate could also be synthesized by the two atom cage expansion of the siladecaborane, MeSiB9Hi2(NHMe2) depicted in Scheme 3.3-4 [15, 16]. 

However, in terms of purification, it is more efficient to prepare it by cage expansion according to... 

The syntheses of the heteroboranes often involves the addition of heteromolecules to nido-boranes, in so called cage expansion reactions. Two of the most used borane precursors are pentaborane(9) (nido-BsHg) and decab-orane(14) (niT/o-BioHn) both of which are shown in Figure 2. 

Scheme 12.38 First cinchona cage expansion of 9-ep/-configured bromoquinine epi-la-Br and epi-2a-Cl mediated by silver ion.

Scheme 12.39 First cinchona cage expansion of quincorine and quincoridine. Distinct bridgehead iminium ions 109 + and 110+ and their stereospecific capture by nucleophiles.

Scheme 12.41 First cinchona cage expansion ofepi-configured O-mesylated quinine ep/-la-OMs and quinidine ep/-2a-OMs Preparation of a-amino ethers 107-OMe and 108-OMe. Reagents and conditions (a) NaOBz (2 equiv), MeOH, rt, 2h.

Scheme 12.45 General cinchona alkaloid cage expansion and solvolysis scheme — educt-product correlations (a) prototype (1-azabicyclo[2.2.2]oct-2-yl)methyl-X rearrangement (X = leaving group) (b) cinchona rearrangements illustrated for Q (6 -R = OMe) and Q (6 -R = H).

The [2.2.2]azabicyclic cage of the alkaloids is not immutable. The first and second cage expansions have been discovered only during the past decade. A general cinchona alkaloid solvolysis and rearrangement scheme and a unified theory have been presented. Classical solvolysis chemistry with conventional hydrocarbon substrates is complemented. The resulting azabicyclo[3.2.2]nonanes have hardly been studied. 

Cage closure from nido or arachno to closo commonly occurs on heating, though disproportionation may occur simultaneously [Eq. (3.4)]. Reaction with diborane can be used to effect cage expansion [Eq. (3.5)] ... 

Cage expansion of the carborane nido-2,3- C2H )2C2B4Hq results from reaction with BH3-N(C2Hs)3 at 140 C to form ctoso-2MO2 5)202BsHs [17]. 

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