Cubane amides

The regioselective syn, vicinal lithiation of cyclopropane and cubane amides has been reported. Transmetalation to organomercury or zinc compounds facilitates functionalization, as shown in Scheme 43. 

Zinc carbamate complexes are well known, and the structural types and stabilities can be compared with thiocarbamates and dithiocarbamates which are discussed in Sections 6.8.11.1.3 and 6.8.7.1.4482 Carbamates of zinc can be formed from the reaction of carbon dioxide with alkylzinc alkyl amides and further reaction with alkylzinc can give a distorted cubane structure.483 The tetrameric diethylcarbamate species initially formed can also be used to produce monomeric or dimeric carbamate structures in reaction with amines tetramethylethylenediamine forms a monomer [(Me2NCH2)2Zn(02CN(C2H5)2)2] with an octahedral zinc center and pyridine forms a dimer[CsH5NZn2Me(02CN(C2H5)2)3] with tetrahedral zinc centers.484... 

Only a small number of heavier group 1 metal primary amides has been structurally characterized. Table 2 lists six compounds, three containing sodium and three containing cesium. The structures characterized contain the well-established M2N2 ring motif to build dimers 280 and 281, a tetrameric cubane 282, and polymers 283-285. The... 

Eaton and co-workers also reported the synthesis of 1,3,5-trinitrocubane and 1,3,5,7-tetranitrocubane (39) ° The required tri- and tetra-substituted cubane precursors were initially prepared via stepwise substitution of the cubane core using amide functionality to permit ort/jo-lithiation of adjacent positions. The synthesis of precursors like cubane-1,3,5,7-tetracarboxylic acid was long and inefficient by this method and required the synthesis of toxic organomercury intermediates. Bashir-Hashemi reported an ingenious route to cubane-1,3,5,7-tetracarboxylic acid chloride (35) involving photochemical chlorocarbonylation of cubane carboxylic acid chloride (34) with a mercury lamp and excess oxalyl chloride. Under optimum conditions this reaction is reported to give a 70 8 22 isomeric mixture of 35 36 37... 

Eaton and co-workers ° synthesized the cubane-based dinitrourea (42) via iV-nitration of the cyclic urea (41) with nitric acid-acetic anhydride. Cubane-based nitramide (43) is prepared from the IV-nitration of the corresponding bis-amide with acetic anhydride-nitric acid. Bis-nitramine (44) is prepared from the IV-nitration of the corresponding diamine with TFAA-nitric acid. ... 

It has been shown that lithiation with lithium amides can also be regioselective (see 2-21).277 In the case of the cubane derivative 30, a saturated unactivated position was regio-selectively lithiated.278... 

The amide method was found to be convenient and straightforward in many cases. An example is the synthesis of soluble barium terr-butoxide, which has a cubane structure (106b). The preparation of this compound by other routes (e.g, direct action of metals with alcohols or chloride-alkoxide interchange), sometimes tends to be complicated due to the incorporation of chloride or oxide moieties within the structural framework of the final alkoxide product. 

Transamination reactions. Most of the known imidotin cubanes of the type [Sn( a3-NR)]4 have been prepared via transamination reactions between a tin amide reagent and a primary amine. The first example was reported by Veith in 1979 and involved the reaction of the cyclic diazastannylene 1 (Scheme 2.2.2) with ferf-butylamine at 50 °C. However, the initial reaction of these reagents produces either the tricyelic compound 2 or the yeco-cubane 3, depending on the reaction stoichiometry (from molar ratios of lifBuNHa of 2 1 or 3 4, respectively). Compounds 2 and 3 are converted to the cubane... 

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