Exchange with boranes

Exchange with boranes can also be used to prepare alkenylzinc reagents.138... 

Convenient procedures are available for isomerically uncontaminated borinane which can be obtained by the hydroboration of 1,4-pentadiene in a 3 2 ratio, followed by thermal isomerization and exchange with borane ... 

The mechanisms of these exchange reactions as well as of the related exchanges with boron halides, tris(dialkylamino)boranes, and boron alkyls has been interpreted to proceed through a four-center transition state (255, 258, 260). 

Lithioferrocene (322) or dilithioferrocene (323) can also be prepared, and then utilized in situ, from the corresponding halo- or dihaloferrocenes by halogen-metal exchange with alkyl lithiums. Alternatively, monohthiation of l,l -dibromoferrocene gives rise to anion (351), which may be reacted with an electrophile in order to afford additional ferrocene derivatives. In this way, monophosphine oxazoline ferrocene (340) is prepared from bromo oxazoline ferrocene (352), a compound that also is used to prepare chiral-at-phosphorus ferrocenes (353). Other chiral-at-phosphoras ferrocenes (354) are made from (323) and a phosphite borane as the electrophile (equation 80). The phosphorus atoms may also be contained in a ring that possesses chirality the sequences used to prepare this family... 

Bayer and Siebert reported the reaction of 3,3-dimethyl-l-butyne with -BuLi in pentane, followed by the addition of boron trichloride to afford the intermediate dichloro(3,3-dimethylbut-l-ynyl)borane that was hydroborated with dichloroborane formed in situ to give l,l-bis(dichloroboryl)-3,3-dimethylbutene 51 (Scheme 6) <2002ZN1125>. When the latter was subjected to halogen exchange with boron triiodide, it was converted into the corresponding tetraiodide 52, which underwent a redox reaction with hex-3-yne to give the 2-(2,2-dimethylpropylidene)-l,3-diborole 22 in 73% yield. 

Other hand, dialkylquinolinyl boranes can be prepared from halogen-metal exchange with n-BuLi, followed by quenching with R2B OEt or 9-BBN-Br. 

Reactivation of this compound could be achieved through exchange with Al-cocatalysts the presence of borane activators (through alkene insertion into the Zr-allyl bond) or reaction with H2. DFT calculations suggested that reactivation by H2 was the lo west-energy path way NMR evidence has been... 

BCl, BBr, and BI undergo exchange reactions to yield mixed boron hahdes. Exchange reactions also occur with trialkyl, triaryl, trialkoxy, or triaryloxy boranes and with diborane. Anhydrous metal bromides and iodides can be prepared by the exchange reaction of the metal chloride or oxide and BBr or BI (21)-... 

Dialkylquinolinyl boranes 83 and 86 were prepared from halogen/metal exchange of 3-bromoquinoline (70) with n-BuLi followed by quenching with Et2BOMe and Br-9-BBN, respectively. They are then coupled with bromides 84 and 87 to give 3-substituted quinoline derivatives 85 and 88, respectively (85H2375). 

Organozinc reagents have been used in conjunction with a-bromovinylboranes in a tandem route to Z-trisubstituted allylic alcohols. After preparation of the vinylborane, reaction with diethylzinc effects migration of a boron substituent with inversion of configuration and exchange of zinc for boron.176 Addition of an aldehyde then gives the allylic alcohol. The reaction is applicable to formaldehyde alkyl and aryl aldehydes and to methyl, primary, and secondary boranes. 

Tris(diphenylmethyleneamino)borane was obtained according to Eq. (30). Exchange reactions of monomeric and dimeric iminochloroboranes with various fluorides could not be effected. However, this lack of reaction is to be expected, since it is well known from borazine chemistry that substitutions which would require a structural change in order to obtain a stable product will not occur 20>. (Diphenylketimino)trimethylsilane (rather than diphenylketimine lithium) has been utilized successfully to prepare (diphenylmethyleneamino) dihaloboranes. This type of reaction is in accordance with earlier observa-... 

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