Borane complexes reactions

Diborane [19287-45-7] the first hydroborating agent studied, reacts sluggishly with olefins in the gas phase (14,15). In the presence of weak Lewis bases, eg, ethers and sulfides, it undergoes rapid reaction at room temperature or even below 0°C (16—18). The catalytic effect of these compounds on the hydroboration reaction is attributed to the formation of monomeric borane complexes from the borane dimer, eg, borane-tetrahydrofuran [14044-65-6] (1) or borane—dimethyl sulfide [13292-87-0] (2) (19—21). Stronger complexes formed by amines react with olefins at elevated temperatures (22—24). 

Reduction of 3,5,5-tris-aryl-2(5// )-furanones 115 (R, R, R = aryl) with dimethyl sulfide-borane led to the formation of the 2,5-dihydrofurans 116 in high yields. However, in the case of 3,4-diaryl-2(5//)-furanones 115 (R, R = aryl R = H or r = H R, R = aryl), the reduction led to a complicated mixture of products of which only the diarylfurans 117 could be characterized (Scheme 36) (88S68). It was concluded that the smooth conversion of the tris-aryl-2(5//)-furanones to the corresponding furan derivatives with the dimethylsulfide-borane complex in high yields could be due to the presence of bulky aryl substituents which prevent addition reaction across the double bond (88S68). 

Borane, 1-methylbenzylaminocyanohydropyrrolyl-, 3, 84 Borane, thiocyanato-halogenohydro-, 3,88 Borane, trialkoxy-amine complexes, 3, 88 Borane, triaryl-guanidine complexes, 2,283 Borane, trifluoro-complexes Lewis acids, 3,87 van der Waals complexes, 3, 84 Borane complexes aminecarboxy-, 3,84 aminehalogeno-, 3, 84 amines, 3, 82, 101 B-N bond polarity, 3, 82 preparation, 3, 83 reactions, 3, 83 bonds B-N, 3, 88 B-O, 3, 88 B-S, 3, 88 Jt bonds, 3, 82 carbon monoxide, 3, 84 chiral boron, 3, 84 dimethyl sulfide, 3, 84 enthalpy of dissociation, 3, 82... 

A comprehensive review of the preparation, reactions, and n.m.r. spectra of phosphorus-fluorine compounds has appeared. This year s literature has been notable for the first detailed applications of ab initio SCF-MO calculations to the problems of bonding in halogenophosphines and their derivatives. - Comparison of the results of such theoretical calculations with experimental data obtained from photoelectron spectra shows a good correlation in the case of phosphorus trichloride and phosphoryl chloride, and of phosphorus trifluoride and its borane complex. ... 

In order to avoid the use of a rather expensive and potentially dangerous borane complex, Bolm et al. have developed an improved procedure for the borane reduction of ketones, which involved two inexpensive reagents namely NaBH4 and TMSCI. The reduction of a series of ketones was examined applying these novel reaction conditions and the same p-hydroxy sulfoximine ligand to that described above (Scheme 10.56). For most ketones, both the level of asymmetric induction and the yield compared favorably to the precedent results. 

Amine-borane complexes are not very reactive toward hydroboration, but the pyridine complex of borane can be activated by reaction with iodine.160 The active reagent is thought to be the pyridine complex of iodoborane. 

Another interesting reaction is the very slow acid-induced rearrangement-hydration of kuomine. This reaction results in the formation of a labile hemiacetal, hydrakouminol (54), and its reduction with a borane complex in... 

This methodology was applied successfully also for the diastereoselective synthesis of a series of P-stereogenic (o-hydroxyaryl)diazaphospholidine - borane complexes 250-257 (yields ranging from 40 to 86%) via the reaction sequence shown in Scheme 61 with a one-pot formation of the appropriate (o-bromoaryloxy) diazaphospholidine-borane complexes 242-249 in yields ranging from 70 to 92% (Scheme 61) [93],... 

Chiral (Acyloxy)borane Complex Catalyzed Asymmetric Diels-Alder Reaction (1 R)-1,3,4-Trimethyl-3-cyclohexene-1-carboxaldehyde. 

Similar to the addition of secondary phosphine-borane complexes to alkynes described in Scheme 6.137, the same hydrophosphination agents can also be added to alkenes under broadly similar reaction conditions, leading to alkylarylphosphines (Scheme 6.138) [274], Again, the expected anti-Markovnikov addition products were obtained exclusively. In some cases, the additions also proceeded at room temperature, but required much longer reaction times (2 days). Treatment of the phosphine-borane complexes with a chiral alkene such as (-)-/ -pinene led to chiral cyclohexene derivatives through a radical-initiated ring-opening mechanism. In related work, Ackerman and coworkers described microwave-assisted Lewis acid-mediated inter-molecular hydroamination reactions of norbornene [275]. 

Aminomethylphosphines are convenient objects for a comparison of phosphorus and nitrogen donor ability in complexation reactions. Coordination compounds of heterocyclic aminomethylphosphines with metals are discussed in Section VII. In this section we present reactions of aminomethylphosphines with boranes (BH3). 

Standard cyclisation methodology was used to access the cyclic monophosphinic acid derivative 78 by reaction of ammonium phosphonate and ethyldiisopropylamine, followed by the addition of chlorotrimethylsilane, with 2,2 -bis (bromomethyl)-l,l -biphenyl. Silane reduction of 78 gave the secondary phosphine. The secondary phosphine borane complex 79 could be used in alkylation or Michael addition reactions. For example the Michael adduct 80 was produced in high yield by treatment of 78 with a NaH suspension in THF followed by the addition of diethylvinylphosphonate . 

The mechanism involves the dissociation of the coordinated borane 15 to generate a monoborane intermediate 16. Coordination of the alkene would generate the alkene borane complex. A /3-borylalkylhydride with B-H stabilization is certainly an important resonance structure of 17. An intramolecular reaction would extrude the alkyl boronate ester product and coordination of HBcat would regenerate the monoborane intermediate. 

The carbanions take up 02 and these take up protons to give hydroperoxides in good yields. But because they are explosive in nature, they are not usually isolated and on reduction with sodium sulphite on trialkyl phosphite give alcohols. Alcohols can also be prepared via hydroperoxy molybdenum complexes and alkyl boranes. These reactions are summarized as follows ... 

CHIRAL (ACYLOXY)BORANE COMPLEX-CATALYZED ASYMMETRIC DIELS-ALDER REACTION (1R)-1,3,4-TRIMETHYL-3-CYCLOHEXENE-1-CAR BOX ALDEHYDE (3-Cyclohexene-1-carboxaldehyda, 1,3,4-trlmethyl-, (-)-)... 

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. 

The authors then go on to measure the kinetics in the presence of two oxazabor-ole catalysts, (92a) and (92b).The rate-determining step is the reaction of the ketone with an oxazaborole-borane complex, with the direct reduction competing with the catalytic cycle (as mentioned above). The oxazaborole reaction, like the direct reduction, is significantly accelerated by the presence of sodium borohydride. 

Tris(trimethylsilyl)silane reacts with phosphine sulfides and phosphine selen-ides under free radical conditions to give the corresponding phosphines or, after treatment with BH3-THF, the corresponding phosphine-borane complex in good to excellent yields (Reaction 4.45) [82]. Stereochemical studies on P-chiral phosphine sulphides showed that these reductions proceed with retention of configuration. An example is given in Reaction (4.46). 

The reductive cleavage of phosphonio-substituents attached to other heterocyclic frameworks was first demonstrated in the reaction of the 3,5-bis-phosphonio-l,2,4-diazaphospholide 15 with NaBH4 or LiBEt3H to yield the zwitterionic borane-complexes 27. Liberation of the free zwitterion 28 was readily feasible by treatment of the complexes with an excess of NEt3 (Scheme 9) [34]. 

An efficient resolntion of the racemic lithinm tert-bntylphosphine-borane complex 203 dnring deprotonation by n-BnLi/(—)-sparteine (11) and alkylation was reported by Liv-inghonse and Wolfe (eqnation 47) . One of the epimers 204/cp/-204 on warming to 0 °C crystallizes during a dynamic thermodynamic resolntion, and reaction with alkyl halides fnmishes the alkylation prodncts 205 with high ee values. Applying dihalides, essentially enantiomerically pure diphosphines snch as 206, besides few of the mcio-diastereomer, were obtained. Borane is removed by treatment with diethylamine to yield the free tertiary phosphines 207. 

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