Diisopropyl boronate, preparation

A better procedure for the preparation of various alkynylbenziodoxoles (136, 139-146) in high yields involves the reaction of triflates 168 and 112 with alkynyltrimethylsilanes according to Scheme 2.48 [283]. Further modification of this approach consists of the reaction of l-acetoxy-l,2-benziodoxol-3(l//)-one with l-alkynyl(diisopropyl)boronates in acetonitrile under reflux conditions [297]. 

The tartrate-derived allylboronates 25 are best prepared by treatment of triisopropyl borate with the appropriate carbanion. The crude diisopropyl boronate 28 is then treated with either enantiomer of diisopropyl tartrate (DIPT) to effect rapid transesterification, giving the boronates 25, 29, and 30 (Equation 4) [47],... 

The allyl boronate esters (R,R)- and (S,S)-1 are prepared by reaction of allylboronic acid, CH2=CHCH2B(OH)2 with l- and D-diisopropyl tartrate.1... 

The synthesis of L-ribose required two significant innovations for its completion. The first was an efficient synthesis of diisopropyl (chloromethyl)boronate (1) via the in situ preparation of (chloromethyl)lithium by addition of butyllithium to a mixture of chloroiodomethane and triisopropyl borate in THF at — 78°C 18. 

S)-Pinanediol (chloromethyl)boronate is prepared by stirring 48.3 g (0.27 mol) of diisopropyl (chloro-methyl)boronate with 46.1 g (0.27 mol) of (S)-pinanediol in 200 mL of diethyl ether overnight. The solution is concentrated and the product is chromatographed on a short column of silica gel and distilled yield 58.8 g (95%) bp 95-100T (0.2 Torr). 

The (E) and (Z) forms of the vinylboron compounds 278 and 279 can be prepared by hydroboration of alkynes and haloalkynes, and their reactions with the (E)- or (Z)-vinyl iodides or bromides 280 and 281 proceed without isomerization the four possible isomers 282-285 can be prepared in high purity. However, for the efficient preparation of the (Z,Z)-dienes 287, the diisopropyl ester of (Z)-alkenylboronic acid 286 should be used. Other boron compounds give poor yields... 

Brown and co-workers developed a novel homoallenyl boronate reagent 169 based on diisopropyl tartrate for the stereoselective homoallenylation of aldehydes 170. The reagent 169 was prepared via homologation of the corresponding allenyl boronate or the alkylation of halomethyl boronate with allenyl Grignard similar to those reported in Scheme 26. The allyl boronate 169 upon reaction with aldehydes furnished the dienyl alcohols 172 with high ee (Scheme 28) <1996JOC100>. 

Fig. 16.16. Stereoselective preparations of cis-alkenyl-boronic acids and the corresponding diisopropyl ester starting with cis-bromoalkenes. The first step involves a Br/Li exchange to form the alkenyl-lithium compound B. This organolithium compound is subsequently transmetalated to give complex C by using B(0/Pr)3.

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