Mohamed Yalpani

Chromium assisted 1,5-sigmatropic rearrangement of hexaethylidenecyclohexane to 1,3,5-triethenyl-2,4,6-triethylbenzene

Abstract Hexaethylidenecyclohexane (I) in dioxane reacts with chromium tricarbonyl-triacetonitrile with double 1.5-sigmatropic hydrogen migration to give the chromium tricarbonyl complex III, the structure of which has been determined by NMR and X-ray analysis. Heating solutions of III results in a further rearrangement to form the chromium tricarbonyl complex of 1,3,5-triethyl-2,4,6-trivinylbenzene (V). The latter releases the ligand IV on prolonged heating in an atmosphere of carbon monoxide.

An outline of the chemistry of bis(9-borabicyclo[3.3.1]nonane)

- The distinctive features in the reactivity of (9H-9-BBN), compared to other tetraakyldiboranes(6) arise primarily from the rigid and usually very stable bicydic structure of the 1,5-cyclooctanediyl residue, which prevents the facile dismutation of the organic groups often observed in the latter, especially at elevated temperatures. - The 1,s-cyclooctanediylboryl group (9-BBN) has gained manifold importance in chemistry for a number of reasons: 1. Highly selective reaction pathways. 2. Enhanced reactivity of exocyclic BC-bond over the endocyclic BC-bonds in the bicyclic C8HI4B system. - 3. Facile preparations of various pure 9X-9-BBN borane reagents. - 4. New informative, easily isolable 9-BBN crystalline solids.

Produkte der Carbodiimid-Hydroborierung mit (9H -9-BBN)2 [1] / Hydroboration Products of Carbodiimides with (9H-9-BBN)2 [1]

The hydroboration of H11C6N=C=NC6H11(A) with (9H-9-BBN)2 (C2) gives H11C6N= C(H)N(C6H11)BC8H14 (1), which reacts with 9H-9-BBN to form the six-membered heterocycle mixed dimer (2). Compound 2 crystallizes in the monoclinic space group C 2/c, a = 27.776(3). b = 17.140(2), c = 12.302(2) Å, β = 113.31° (at 120 K). - On heating. 2 is transformed by intramolecular hydroboration into H2C[N(C6H11)B(C8H14)]2 (3a). - 1 reacts with Et2O-BF3 to give 9F-9-BBN (4) and (5). - The total hydroboration of H5C6N=C=NC6H5 (B) with C2 affords H2C[N(C6H5)B(C8H14)]2 (3b).

Carbonylation of BH-boranes; evidence for a Fischer—Tropsch type reaction

Abstract Bis(9H-9-borabicyclo[3.3.1]nonane) is readily carbonylated under about 50 bar pressure of carbon monoxide at 100°C. Bis(1,5-cyclooctanediyl)-2,5-dibora-1,4-dioxane (1a) is formed quantitatively. Reaction of 1a at room temperature with acetic or propionic acid affords the corresponding 9,10-diacyloxy-bicyclo[3.3.2]decanes 2a and 2b. Thermolysis of 1a gives the tris-(5-cyclononenyl-boroxine 4 as the main product. The expected tris(bicyclo[3.3.1]nonanylboroxine) 3 in formed only in a side reaction. The carbonylation of tetraethyldiborane(6) is easier, requiring about 10–20 bar of carbon monoxide pressure at room temperature. The product consists of a mixture of 2,5-dibora-1,4-dioxanes with partially homologated alkyl substituents. The homologation proceeds in a manner analogous to that of the Fischer-Tropsch reaction.

Monomeric and dimeric acyloxydialkylboranes

The carboxylic acids RCO2H [R = Buta, Et b, 3,4,5-(MeO)3C6H2c, 4-MeOC6H4d, Ph e, 2,4,6-Me3C6H2f, 2,6-Cl2C6H3g, or 3,5-(CF3)2C6H3h] were treated with triethylborane or with bis(9-borabicyclo[3.3.1]nonane) to give the acyloxydiethylboranes 1a–1h and the 9-acyloxy-9-borabicyclo[3.3.1]nonanes)2a–2h, respectively. Compounds 1a–1h are largely unassociated in non-polar solvents (11B NMR, IR spectroscopy). As pure liquids, or in the solid state, they form equilibrium mixtures of monomeric and associated (dimeric) molecules (IR spectroscopy). Compounds 2a–2f are completely associated as pure liquids and in the solid state, but only weakly associated in non-polar solvents. Based on the crystal structure of dimeric 2e, it is proposed that, when associated, derivatives of both 1 and 2 form cyclic dimers.