Boranes tert.

Boran (tert.-Butyl-trimethylsilyl-amino)-dimethyl-XIII/3b, 118... 

Boran tert.-Butylimino-(pentafluor-phenyl)- XIII/3a, 11... 

Boran tert.-Butyl-(4-fluor-benzylidenamino)-hydro-XIII/3b, 137... 

Sodium bis-(2-methoxyethoxy)aluminium hydride (ref. 84) and lithium tri-tert-butoxyaluminium hydride (ref. 85) showed excellent stereoselectivity for podophyllotoxin compared with other reagents. However, these reagents have the disadvantage that low temperature (-75 C) is required to obtain satisfactory yield. Although the stereoselectivity was inferior to that of the above-mentioned aluminium hydride complexes, borane-terf-butylamine complex (ref. 86) and borane ammonia complex (ref. 87) gave the products in more than 90% yield. The reactions proceeded at room temperature, and borane-tert-butylamine complex did not require the use of a nitrogen stream. 

Triathylamin-Boran reduziert sek. und tert. Halogen-alkane in fl. Schwefeldioxid Oder Nitromethan zu Koh-lenwasserstoffen (s. S. 388). 

Lithiumboranat10 N atriumboranat11 Kaliumboranat12 tert.-Butylamin-Boran13 Dimethylamin-Boran13 1,2-Diamino-athan-Boran 4 Pyridin-Boran15... 

Unter normalen, aprotischen Bedingungen in Pyridin oder in Gegenwart eines tert. Amins setzt sich Natrium-boranat nur bis zur Amin-Boran-Stufc 4 um z. B. ... 

Zur Spaltung von Tetrahydrofuran-Ringen kann auch Lithium-tri-tert.-butyl-oxy-hydrido-aluminat/Triathyl-boran verwendet werden. Die Reaktion wird in Tetrahydropyran durchgefiihrt, das vom Reagens nur langsam angegriffen wird. 

Trialkylboranes react rapidly and in high yields with a-halo ketones,a-halo esters, a-halo nitriles, and a-halo sulfonyl derivatives (sulfones, sulfonic esters, sulfonamides) in the presence of a base to give, respectively, alkylated ketones, esters, nitriles, and sulfonyl derivatives. Potassium tert-butoxide is often a suitable base, but potassium 2,6-di-tert-butylphenoxide at 0°C in THF gives better results in most cases, possibly because the large bulk of the two tert-buXy groups prevents the base from coordinating with the R3B. The trialkylboranes are prepared by treatment of 3 mol of an alkene with 1 mol of BH3 (15-16). With appropriate boranes, the R group transferred to a-halo ketones, nitriles, and esters can be vinylic, or (for a-halo ketones and esters) aryl. " °... 

The residual pasty solid was purified by column chromatography over silica gel (//-hexane ethyl acetate = 8 1) to afford tert-butyl (dimethyl)phosphine-borane (1) 5.29 g (86 %) as white crystals. 

Borane-diethylaniline complex (815 mg) was added to the resulting mixture. A solution of l-(tert-butyldimethylsilyloxy)-3-oxo-2-trityloxyiminooctade-cane (1.68 g) in dry tetrahydrofuran (5mL) was added dropwise using a syringe pump over 1 hour at room temperature. 

The thermal isomerization of tert. -butyl-diisobutylborane to triisobutylborane and the stepwise isomerization of triisopropyl and tri-sec.-butyl boranes to the corresponding straight-chain isomers have been studied over a range of temperature, both neat and using either the end product trialkylborane or diglyme as solvent117 . In all cases the reactions were first order and showed no solvent effect. 

S)-(-)-CITRONELLOL from geraniol. An asymmetrically catalyzed Diels-Alder reaction is used to prepare (1 R)-1,3,4-TRIMETHYL-3-C YCLOHEXENE-1 -CARBOXALDEHYDE with an (acyloxy)borane complex derived from L-(+)-tartaric acid as the catalyst. A high-yield procedure for the rearrangement of epoxides to carbonyl compounds catalyzed by METHYLALUMINUM BIS(4-BROMO-2,6-DI-tert-BUTYLPHENOXIDE) is demonstrated with a preparation of DIPHENYL-ACETALDEHYDE from stilbene oxide. A palladium/copper catalyst system is used to prepare (Z)-2-BROMO-5-(TRIMETHYLSILYL)-2-PENTEN-4-YNOIC ACID ETHYL ESTER. The coupling of vinyl and aryl halides with acetylenes is a powerful carbon-carbon bond-forming reaction, particularly valuable for the construction of such enyne systems. 

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