Borane nitroalkenes

Reaction of the salts of primary and secondary alky Initio compounds with diborane in THF solution at 25 °C yields the corresponding hydroxylamines.117 Kabalka has reported the reduction of nitroalkenes to hydroxylamines or amines with a variety of borane and borohydride reagents (Eq. 6.61).118... 

The conjugate addition of phosphorus nucleophiles of various oxidation states and in neutral or metallated form constitutes an efficient and well-known method for C—P bond formation [30]. In the case of phosphanes as nucleophiles especially, the corresponding phosphane-borane adducts have been used in 1,4-additions to Michael acceptors. Following the idea to use a chirally modified phosphorus nucleophile in asymmetric Michael additions to aromatic nitroalkenes, we synthesized the new enantiopure phospite 45 starting from TADDOL (44) with nearly quantitative yield. Due to the C2 symmetry, of the... 

Trialkylboron hydrides react with conjugated nitroalkenes to yield nitronate intermediates via a 1,4-addition of the hydride. The corresponding nitroalkanes are easily obtained by using silica gel to proto-nate the nitronate salt. These reactions presumably occur through a common intermediate (36), which is then hydrolyzed to the nitroalkane or reduced by a borane complex to yield hydroxylamine, after hydrolysis. 

Even sodium borohydride catalyzes the reaction of borane complexes with conjugated nitroalkenes (equation 24). This straightforward approach affords pure hydroxylamines in high yields. As an... 

Since hydroxylamines, as well as their precursor oxime derivatives, are reduced by diborane to amines, the reaction has been extended by reducing the initially formed hydroxylamine intermediates (57) to amines (58). Thus excess borane reduces nitroalkenes (56) to amines (58) in the presence of a catalytic amount of sodium borohydride (equation 32). 

The hydroquinine thiourea catalyst 81a was also identified by Melchiorre and coworkers as a promising catalyst for the asymmetric addition of secondary phosphines 1SS to aromatic nitroalkenes 130 furnishing 156 (obtained after protection with in situ formed borane) [46]. However, the obtained ee values were only moderate (up to 66% ee) (Scheme 9.53). 

Bp3-OEt2 followed hy DiisobutyUduminum Hydride is used for the 1,2-reduction of y-aimno-Q, -unsaturated esters to give unsaturated amino alcohols, which are chiral building blocks for a -amino acids. Q , -Unsaturated nitroalkenes can be reduced to hydroxylamines by Sodium Borohydride and BF3-OEt2 in THF extended reaction times result in the reduction of the hydroxylamines to alkylamines. Diphenylamine-borane is prepared from sodium borohydride, BF3-OEt2, and diphenylamine in THF at 0 °C. This solid is more stable in air than BF3-THF and is almost as reactive in the reduction of aldehydes, ketones, carboxyhc acids, esters, and anhydrides, as well as in the hydrob-oration of alkenes. 

Novel P-stereogenic PCP pincer Pd complexes 308 were designed and prepared in short steps from optically pure tert-butylmethylphosphine borane 306. The optically active Pd-complexes 308 were successfully applied in asymmetric addition of diarylphosphines to nitroalkenes with high yields and good enantios-electivity (Scheme 103) [202]. 

Hydroxylamines have been obtained from reductions of nitroalkenes with borane-tetrahydrofuran, and it has also been shown that catalytic quantities of sodium borohydride greatly accelerate the rates 454... 

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