Allylboronic acid derivative

Three compounds, diallyl (1), (Af-allyWV-phenylamino)-diallylborane (2), (8 11B 44 ppm) and an allylboronic acid derivative (3) (8 nB 32 ppm) were identified by NMR as the products of the reaction of A113B with PhN02 (Scheme 2). 

The enantioselective addition of ally organometallics to carbonyls has become one of the workhorses of organic synthesis. Dennis Hall of the University of Alberta reports (J. Am. Chem. Soc. 125 10160, 2003) the scandium triflate catalysis chiral allylboronic acids become more effective tools. The best of these, the Hoffmann camphor derivative 2, adds to aldehydes under Sc(OTf), catalysis with excellent enantiomeric excess. The reaction works equally well for methallyl, and for the E and Z crotyl boronic acids. The crotyl derivatives react with the expected high diastereocontrol. A limitation to the boronate additions is that branched chain aldehydes give low yields. 

By a similar method, the (Z)-crotylborate is synthesized from cA-2-butene in 70-75% yield with a 98% isomeric purity. The tartrate esters of allylboronic acids are an excellent reagent for asymmetric allylboration of carbonyl compounds. Allyl(diisopinocampheyl)borane [51] and the allylic boron derivatives of ester and amide, such as camphordiol [52], pinanediol [53], 1,2-diphenyl-1,2-ethylenediamine [54], have also been successfully used for asymmetric allylboration of carbonyls. 

Scheme 20 Reactivity of 29 in Suzuki-Miyaura coupling of allylboronic acid pinacol ester derivatives...

The cyclic allylboronic acids are excellent substrates also for diastereoselective dihydroxylation. Scheme 7 demonstrates the utility of this reaction in preparing functionalized xylitol derivative 85 with >20 1 diastereoselec-tivity <2002AGE152>. 

Hunt and Roush <1995TL501> achieved a synthesis of swansonine 230 via a stereoselective allylation of a silyl allylboronate derived from tartaric acid followed by a Tamao-Fleming oxidation to introduce the C-2 hydroxy functionality (Scheme 54). 

An allylboronate derivative of tartaric acid developed for enantioselective allylation of aldehydes is readily recyclable without losing selectivity.182... 

Several methods promoted by a stoichiometric amount of chiral Lewis acid 38 [51] or chiral Lewis bases 39 [52, 53] and 40 [53] have been developed for enantioselective indium-mediated allylation of aldehydes and ketones by the Loh group. A combination of a chiral trimethylsilyl ether derived from norpseu-doephedrine and allyltrimethylsilane is also convenient for synthesis of enan-tiopure homoallylic alcohols from ketones [54,55]. Asymmetric carbonyl addition by chirally modified allylic metal reagents, to which chiral auxiliaries are covalently bonded, is also an efficient method to obtain enantiomerically enriched homoallylic alcohols and various excellent chiral allylating agents have been developed for example, (lS,2S)-pseudoephedrine- and (lF,2F)-cyclohex-ane-1,2-diamine-derived allylsilanes [56], polymer-supported chiral allylboron reagents [57], and a bisoxazoline-modified chiral allylzinc reagent [58]. An al-lyl transfer reaction from a chiral crotyl donor opened a way to highly enantioselective and a-selective crotylation of aldehydes [59-62]. Enzymatic routes to enantioselective allylation of carbonyl compounds have still not appeared. 

A chiral allylic alcohol (3-carbanion equivalent has also been developed which utilizes a DIPT-modified E)-y-(dimethylphenylsilyl)allylboronate reagent. This method involves treating the product homoallylic alcohol with Dimethyl-dioxirane and subjecting the derived epoxide to an acid-catalyzed Peterson elimination. This sequence has been applied in the synthesis of the trioxadecalin ring system of the mycalamides (eq 10). ... 

The biologically important 2-deoxypentoses can be prepared readily by the two-carbon chain elongation of 2,3- -isopropylidene-D-glyceraldehyde following Roush s allylation method (Scheme 13.54), relying on the highly diastereoselective additions of enantiomerically pure allylboronates derived from (R,R) and (5, 5 )-tartaric acid [100]. Similarly, the 2,6-dideoxyhexose derivative 155 was obtained by Roush and Straub (Scheme 13.54) [101]. 

Kabalka et al. have investigated the Pd-catalyzed eross-eoupling reaction of MBH acetates and bis(pinacolato)diboron to produee 3-substituted-2-alkoxy-carbonyl allylboronates 371, whieh ean be further transformed into stable allyl trifluoroborate salts 372 by addition of exeess aqueous KHF2. The allylboronate 371 and allyltrifluoroborate derivatives 372 react with aldehydes to afford functionalized homoallyhc alcohols 373 and 374, respectively, stereoselectively in the presence of Lewis acid (Scheme 3.166). ... 

Optically active allylboronates bearing chiral auxiliary located at the boron atom found widespread applications in asymmetric synthesis. Enantiomerically enriched a-alkylidene-y-lactones and lactams can also be synthesized following such a synthetic approach. VUlieras et al. (41, 45] demonstrated the potential of chiral allylboronates derived from 2-phenyl-2,3-bomanediol, ephedrine, or norephedrine for this purpose. Chiral allylboronates 46a,b were obtained in a sequence of reactions involving transformation of achiral precursors 32 into the corresponding boronic acids 44 followed by their esterification with enantiomerically pure diol or 1,2-aminoalcohol 45 (Scheme 4.10). In the case of methyl-substituted derivatives 32b (R = Me), initial composition of E- and Z-isomers was transferred to the target allylboronates 46b. Importantly, the isomeric mixture was separated by means of the column chromatography. 

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