B-methyl-9-BBN

Lithium dialkyl-9-borabicyclo[3.3.1]nonane ate complexes react with acetyl chloride via hydride transfer to form cz. s-bicyclo[3.3.0]oct-1 -yldialkylboranes.11 The conversion of B-methyl-9-BBN to 63 upon sequential treatment with methyl-lithium and acetyl chloride (93 % yield) illustrates the procedure. As shown in Scheme 17, these organoboranes can serve as valuable intermediates for the preparation of a variety of 1-substituted [Pg.62]

Although the reaction of alkylboronic acids is significantly slower than that of trialkylboranes, methylboroxine (MeBO)3 or methylboronic acid exceptionally alkylates bromo- and chloroarenes [125, 126]. Methylation of electron-poor bromoarenes was efficient, whereas prolonged reaction time was required for more electron-rich substrates. The reaction times can be shortened by use of the polar solvent DMF at 115 °C. B-Methyl-9-BBN and its oxy-derivative (48) [127] undergo methylation of aryl and vinyl halides under more mild conditions (Scheme 22). 

The reaction involves the formation of carbanions that are stabilized by boryl groups . Similar carbanions are prepared from 9-methyl-9-borabicyclo[3.3.1]nonane (B-methyl-9-BBN), 9-alkenyl-9-borabicyclo[3.3. l]nonanes(B-alkenyl-9-BBN) , or alkenyldisiamylboranes with 2,2,6,6-tetramethylpiperidine (Li-TMP) in tetrahydro-furan (THF) ... 

The fiist successful attempt to deprotonate a simple all lborane is shown in equatitm (12). B-Methyl-9-BBN (10) was reacted wid) a variety of lithium amides and the yield of (12) estima by deuterium incorp( ation on quenching with D2O. Neither lidiium diediylamide nor litUum diisopropyl-amide gave any of (12) at all, but the hindered piperidide (11) (LTTMP) produced up to 75% of (12) using 100% excess of base. 

Table 7.10 Reaction of B-aryl- and B-methyl-9-BBN with a-bromoketones [2b]...

Gray et al. reported the coupling of aryl halides with trimethylboroxine 145 in the presence of Pd(PPh3)4 and NajCO, to cause methyl transfer thereby avoiding the use of air-sensitive B-methyl-9-BBN (Scheme 28.40). ... 

Allyllithium gives even higher yields of B-allyl-9-BBN than allylaluminum sesqui-bromide. However, the stoichiometry of the reaction must be controlled to avoid the formation of a diallyl ate complex, and the isolation of product is not simple. Alkylations of B-methoxy-9-BBN with the RMgX reagents meet with limited success. Only the methyl group is quantitatively transferred. Lower yields are obtained with other groups , e.g., n-Bu (42%), Ph (27%). 

B (3-Methyl-2-butyl)-9-borabk cIof3.3.l nonane (B-Siamy]-9-BBN) CN... 

As a useful alternative to carbonylation, the Brown dichloro-methyl methyl ether (DCME) process has been effectively used for the synthesis of 9-alkylbicyclo[3.3.1]nonan-9-ols. 2 The ketone bicyclo[3.3.1]nonan-9-one (eq 29) has also been prepared from a hindered B-aryloxy-9-BBN derivative, with simple B-alkoxy-9-BBN derivatives failing to undergo this process. However, most borinate esters are smoothly converted to ketones through this process, including germa- and silaborinanes (eq 30). In these cases, 9-BBN-H provides the essential 1,5-... 

The czs-vinyl-9-BBN, prepared from (Z)-l-iodo-3-methyl-l-butene via lithi-ation, followed by treatment with B-OMe-9-BBN undergoes condensation with high stereospecificity with benzaldehyde to give the corresponding ds-allylic alcohol in moderate yield (Eq. 6.6) [5]. 

Allylboration of aldehydes and ketones with B-crotyl-9-BBN affords only the rearranged product (Eq. 6.8 Table 6.7) [1]. Monomeric formaldehyde gives 2-methyl-3-buten-1 -ol. 

B-Siamyl-9-BBN, [ B-(3-methyl-2-butyl)-9-BBN] [20], is prepared by the hy-droboration of 2-methyl-2-butene with 9-BBN. The reagent reduces a variety of functionalized aldehydes to the corresponding alcohols (Table 25.9 Chart 25.11) [21]. 

Table 25.13 Reduction of esters by lithium borohydride in refluxing ether in the presence of B-methoxy-9-BBN or methyl borate [39]...

AD-mix-P 9-BBN Bn Boc Bz BOM CDI m-CPBA CSA Cy DBU DDQ DEAD DIAD DIBAL-H DIPT DME DMF DMAP DMSO EDC HMPA HOBT KHMDS LDA MEM MOM MoOPH NaHMDS NBS NMM NMO Piv PMB Reagent for Sharpless asymmetric dihydroxylation 9-Borabicyclo[3.3.1 ]nonyl Benzyl t-Butoxy carbonyl Benzoyl B enzyloxy methyl Carbonyldiimidazole m-Chloroperoxybenzoic acid Camphorsulfonic acid Cyclohexyl 1,8 -Diazabicy clo[5.4.0] undec-7-ene 2,3 -Dichloro-5,6-dicyano-p-benzoquinone Diethyl azodicarboxylate Diisopropyl azodicarboxylate Diisobutylaluminum hydride Diisopropyl tartrate Dimethoxyethane A,N-Dimethylformamide 4-Dimethylaminopyridine Dimethyl sulfoxide N-(3-Dimethylaminopropyl)-A -ethylcarbodiimide Hexamethylphosphoramide 1 -Hydroxybenzotriazole Potassium hexamethyldisilazane Lithium diisopropylamide Methoxyethoxymethyl Methoxymethyl Oxidodiperoxymolybdenum(pyridine)(hexamethylphophoramide) Sodium hexamethyldisilazane N - Bromosuccinimide A-Methylmorpholine A-Methylmorpholine A-oxide Pivaloyl /j-Methoxybenzyl... 

Monohydroboration of allenes with 9-BBN places the boron atom exclusively at the terminal position. Thus, 3-methyl-l,2-butadiene gives B-3-methyl-2-butenyl-9-BBN as the only product (Eq. 43)96). However, such a procedure for the preparation of allylic boranes by the hydroboration of conjugated dienes and allenes is not a general... 

Most recently, B-halo-l-alkenyl-9-BBN s have revealed to undergo a 1,4-addition reaction to ae,P-unsaturated ketones such as methyl vinyl ketone. Hydrolysis of the initially formed intermediates produces the corresponding (Z)-5-halo-y,5-unsaturated ketones in good yields stereospecifically (>98%),88). In the reaction with methyl vinyl ketone, the major products isolated after hydrolysis are not the expected halo-enones but the aldol adducts, which are readily converted into the halo-enones by treatment with sodium hydroxide, as depicted in Scheme 3. No aldol adducts are formed in the case of enones other than methyl vinyl ketone. 

With smaller B substituents, the m-erilolate forms selectively. Here, the boron is part of a bicyclic structure known as 9-BBN (9-borabicyclononane—you will meet this in Chapter 47). The bicyclic part may look large but, as far as the rest of the molecule is concerned, it s Tied back behind the boron, and the methyl group can easily lie cis to oxygen. The ds-enolate then gives syn aldol products. Di-tt-butylboron triflate (B BOTf) also gives cis-enolates. 

Probkm 28.28 Using 9-BBN plus any alkenes and unhalogenated acids or ketones, outline all steps in the synthesis of (a) 2-heptanone (b) 4-methylpentanoic acid (c) 4-methyl-2-hexanone (d) l-cyclohexyl-2-propanone (e) ethyl (trans Z-methylcyclopentyl)acetate (f) l>phenyl-4-methyM-pentanone (g) i-cyclopentyl-33 dimethyl-2-butaBone. 

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