Diborane generation

A solution of 28.2 g (0.30 mole) of norbornene in 100 ml of THF is placed in the flask. The gas dispersion tube is immersed in the reaction liquid and connected with Tygon tubing to a 250-ml three-necked flask serving as the diborane generator. 

Hydroboration of alkenes in non-ethereal solvent has been reported using diborane generated in situ from a quaternary ammonium borohydride and bromoethane (see Section 11.5). Almost quantitative yields of the alcohols are reported [e.g. 1 ]. As an alternative to the haloalkane, trimethylsilyl chloride has also been used in conjunction with the ammonium borohydride [2]. Reduction of the alkene to the alkane also occurs as a side reaction (<20%) and diphenylethyne is converted into 1,2-diphenylethanol (70%), via the intermediate /ra 5-stilbene. 

The ESR spectra of a series of triarylboron anion radicals have been determined and show selective line-broadening effects (95). The radical anions of diborane, generated in an argon matrix at 77 K by irradiation with a-rays have been studied by ESR (121). The vanadium-aluminum complex obtained on mixing dichlorobis(7r-cyclopentadienyl)vanadium with ethylaluminum dichloride, a system that catalyzes the polymerization of ethylene to give a polymer with good characteristics, has been characterized by ESR and ultraviolet studies (44). 

Tetrahydrofuran (350 cm3), sodium borohydride (14.1 g) and (la,5a,6a)-3-N-benzyl-6-nitro-2,4-dioxo-3-azabicyclo[3.1.0]hexane (35.0 g, mmol) obtained above were stirred under nitrogen for 0.25 h and then treated dropwise with boron trifluoride-THF complex containing 21.5% BF3 (44.9 cm3) so that the exotherm was controlled to <40°C. After addition was completed, the reaction mixture was stirred for 3 h at 40°C, quenched slowly with water/THF 1 1 (70 cm3) to avoid excessive foaming, and stirred for 0.5 h at 50°C to ensure that the quench of unreacted diborane generated in situ was completed. The quench formed a salt slurry which was filtered and washed with THF (140 cm3) the combined filtrate was partially concentrated, diluted with water (350 cm3) and further concentrated to remove most of the THF, and extracted with ethyl acetate (140 cm3). The resulting ethyl acetate solution was concentrated to afford the (la,5a,6a)-3-N-benzyl-6-nitro-3-azabicyclo[3.1.0]hexane as a clear oil (30.6 g, 97%). 

The lactone ring in decinine (2) was reduced to the cyclic ether (34) with diborane generated from sodium borohydride and boron trifluoride. The Emde degradation of (34) afforded a piperidine derivative (35a). The Cyanogen bromide N-demethylation of the methyl ether (35b) followed by... 

The structure of B4H10 is shown below at the left. Adjacent to it is one structure proposed earlier which is a dimer of diborane. Generate and compare isoelectronic hydrocarbon analogs of the two valence isomers. 

Recent methods for the cleavage of allyl ethers that have that have yet to be tested on the anvil of complex target synthesis include (a) diborane generated in situ by reaction of sodium borohydride with iodine in THF at 0 °C (cyanoT ester, nitro, acetonide and tetrahydropyranyl groups survive) 434 (b) cerium(Ill) chloride and sodium iodide in refluxing acetonitrile (benzyl. THP and Boc groups survive) 435 (c) iodotrimethylsilane in acetonitrile at room temperature 436 and (d) DDO in wet dichloromethane (secondary allyl ethers, benzyl, acetate and TBS groups survive).437... 

Diborane generated by dropwise addition of NaBI-14 in diglyme to BFg-etherate in the same solvent swept by Ng into a soln. of 7-benzyloxy-2,3-dihydro-9-formyl-l-oxo-lH-pyrrolo[l,2-a]indole in tetrahydrofuran, allowed to stand 16 hrs., then treated with methanol to destroy excess diborane 7-benzyloxy-2,3-dihydro-9-hydroxymethyl-l-oxo-lH-pyrrolo[l,2-a]indole. Y 67%. W. A. Berners, R. H. Roth, and M. J. Weiss, Am. Soc. S6, 4612 (1964). 

Diborane, generated by addition of sodium boron hydride to boron fluoride etherate in dry diglyme, introduced during 1.5 hrs. with periodic sweeping with... 

J-Methylallyl chloride in diglyme flushed with Ng, then diborane generated from NaBH4 and BFg-etherate passed in with stirring at 0°, allowed to stand 1 hr. at 0°, again flushed with Ng NaOH added slowly with vigorous... 

Diborane generated from NaBH4 in diglyme and BFg-etherate carried with Ng during 2 hrs. into an ethereal soln. of frans-2,2,5,5-tetramethyl-3-hexene, stirring... 

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