Preparations and Reactions of Organoboranes

The chemistry of 1-boraadamantane has been explored further. Triphenylphosphorus ylides react with the tetrahydrofuran adduct to give a stable compound which can be thermally rearranged to 4-alky1-3-borahomoadamantanes.Adducts of benzonitriles are formed in a similar way and these rearrange at 200 to the 

Treatment of l-(diisopropylamino)-3-borolene with HeaCLi gives the borole dianion (10) which reacts with chlorotrimethylsilane to give the disubstituted 2-borolene. 2 n should be possible to make a similar pentaalkyl dianion from a 2,5-distannyl-3-borolene since at room temperature both trimethylstannyl groups migrate around the ring. 

Amino substituents have made it possible to isolate a less energetically favourable isomer of CijB2H6 with the classical structure (11) which dynamic n.m.r. measurements show to be in equilibrium with structure (12) in solution.  

The redox behaviour of p-( R2B)2C6Hi4 (R = mesityl) indicates that such systems behave as mirror images of -phenylenediamines. 

5-tetraborinane (13) has been synthesised and its crystal structure determined showing that the molecule prefers the chair con fo rmat ion.  

Two novel routes to triethylborane have been reported. Irradiation of bromoethane and aluminium powder with ultrasound gives ethyl aluminium sesquibromide which on treatment with triethoxyborane gives triethylborane in good yields and a laser initiated gas phase reaction between diborane and ethene gives yields of upto 91%. Allylic boranes have been prepared from allylpotassiiim derivatives and chloroboranes. Hydrolysis leads to the Isomerised olefin and the technique has been used to transform (+)-a-pinene into (+)-3-pinene. Condensation reactions between allylboranes and acetylenes have been developed into a convenient method for the synthesis of bicyclo[3.3.l]nonane derivatives. Mainly linear alkyl derivatives of 9-BBN have been synthesised from the, reaction of iron carbonyls and the organoborane in a Fischer-Tropsch type reaction.  

A simple preparation of symmetrical and unsymmetrical borinic esters from selected boronic esters and organollthium reagents has 

Bis(diiodoboryl)raethane reacts with hex-3-yne or but-2-yne to give 4,5-dialkyl-l,3-diiodo-2,3-dihydro-l,3-diboroles (1,3-diborolenes) in which the iodo functions can be readily substituted by a wide range of other groups to give (4).  

Methods for the preparation of air stable trimethylsilyl substituted trivinylboranes and 9-halo-9-borafluorenes (which are readily converted into methoxy, methylthio and diethyl amino derivatives) have been published. The ability of various cuprates to transfer organo groups to 9-BBN has been investigated and the reactions of aromatic organo copper compounds with organoboranes probed.  

An allene isoster (9) has been isolated and its reactions with a range of reagents studied. A kinetically stable and chemically inert iminoborane (MesSi)sCBNSiMea has been isolated. Chemical and spectroscopic evidence has also been obtained for simple boraethenes XBCHz (X = 0Me,NMe2).  

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