9-Borabicyclo nonane synthesis

The thioboration of terminal alkynes with 9-(alkylthio)-9-borabicyclo[3.3.1]-nonanes (9-RS-9-BBN) proceeds regio- and stereoselectively by catalysis of Pd(Ph,P)4 to produce the 9-[(Z)-2-(alkylthio)-l-alkeny)]-9-BBN derivative 667 in high yields. The protonation of the product 667 with MeOH affords the Markownikov adduct 668 of thiol to 1-alkyne. One-pot synthesis of alkenyl sulfide derivatives 669 via the Pd-catalyzed thioboration-cross-coupling sequence is also possible. Another preparative method for alkenyl sulfides is the Pd-catalyzed cross-coupling of 9-alkyl-9-BBN with l-bromo-l-phe-nylthioethene or 2-bromo-l-phenylthio-l-alkene[534]. 

Olefins with 9-borabicyclo[3.3.1]nonane residues in the synthesis of borane-containing polyolefins 99JOM(581)176. 

The alkynyl reagent 9 was recently introduced for the dia stereoselective synthesis of tertiary propargylic alcohols144. 9 can be prepared as a solid 1 1 complex with tetrahydrofuran by treatment of 9-methoxy-9-borabicyclo[3.3.1]nonane with (trimethylsilylethynyl)lithium, followed by addition of boron trifluoride-diethyl ether complex. The nucleophilic addition of reagent 9 to (R)-2-methoxy-2-methylhexanal (10) afforded a mixture of the diastereomers 11 with a considerable preference to the nonchelation-controlled (3S,4R)-isomer144. 

One such reported example is the synthesis of polypropylene-6-polymethyl-methacrylate (PP-6-PMMA) copolymers utilizing metallocene catalysis and the borane chemistry. In the initial step, PP with chain-end olefinic unsaturations was prepared using metallocene catalysts such as Et(Ind)2ZrCl2/MAO. The unsaturation sites were then hydroborated by 9-borabicyclo[3.3.1]nonane (9-BBN) to produce borane-terminated PP (43) (Fig. 30), which was selectively oxidized and interconverted to a... 

Following this strategy, the stereoselective synthesis of the HU stereoisomer of novel tetra-phosphonatocavitands having lower rim functionality has been reported [66, 67]. Cavitands 12c-12f were respectively synthesized from functionalized resorc[4]arenes Ic-lf. The addition of 1-decanethiol to 12f in the presence of 9-borabicyclo[3.3.1]nonane (9-BBN) in THF afforded cavitand 12g in 80 % yield (Scheme 15). 

It has been shown that the cyclization step of 3-halopropylmalonic esters to give cyclobutane-1,1-dicarboxylatcs, e.g. 3. is rate-determining.4 A convenient synthesis of cyclobutyl derivatives via hydroboration has been reported.5 In this case, 4-tosyloxybut-1-yne was bishydroborated with 9-borabicyclo[3.3.1]nonane (9-BBN), and this was followed by treatment with methyllithi-um to give 9-cyclobutyl-9-BBN 4 in 65% yield.5 24... 

More recently, boranes such as diisopinocampheylborane and a-iso-pinocampheyl-9-borabicyclo[3.3.1]nonane have been shown to be valuable reagents for the synthesis of chiral compounds.10 The reaction of borane with a-pinene gives diisopinocampheylborane... 

Hydroboration of terminal acetylenes with boron halides permits the stereospecific synthesis of ( )-l-chloro(or bromo)alk-l-enes919. BBr3 adds to terminal acetylenes in a regio- and stereoselective manner to yield /Lhalovinylboranes, which are very useful syn-thons92a 923. B-bromo- and B-iodo-9 borabicyclo[3.3.1]nonane react similarly924"926. 

The synthesis of small strained cyclophanes attracted the attention of chemists for many years because the forced proximity of atoms leads to unusual chemical and physical properties. Using the Suzuki reaction to couple a three-legged borane intermediate derived from a triallylsilane 256 to 1,3,5-tribromobenzene, the analogue of Pascal s hydrocarbon was obtained in a single step <19940M3728>. This strategy has been applied to the synthesis of 257 (4% yield) from tris-borabicyclo[3.3.1]nonane (9-BBN) adduct of methyltriallylsilane 256 and 1,3,5-tribromobenzene (Scheme 43). 

Acetylenic ketones are important synthetic intermediates in the synthesis of a variety of natural products. Optically active propargyl alcohols of either configuration are readily available in high optical purity by asymmetric reduction of propargyl ketones with B-3-pinanyl-9-borabicyclo(3.3.1)nonane (Eq. 31). 

Cross-coupling between 1-alkenyl- and arylboron compounds with organic electrophiles have found wide application (see Sect. 1.5.1.1) in organic synthesis [125, 132, 269-271]. The value of this methodology is further realized with the use of alkylboranes, such as B-alkyl-9-borabicyclo[3.3.1]nonanes (B-R-9-BBN), which can be conveniently prepared Ijy hydroboration of olefins [272]. The hydroboration proceeds with high stereoselectivity and chemoselectivity. The choice of phosphines in a catalytic system sometimes affects the chemo- and regioselectivity of the hydroboration. Hydroboration of l-(ethylthio)-l-propyne with catecholborane can be satisfactorily carried out with PdClj (dppf) but the regioselectivity is best for the dppe and dppp complexes of Ni [273]. Notably, PPhj complexes perform poorly. 

For the synthesis of trialkylboranes. hydroboration is carried out with a borane solution in THF or with the borane-methyl sulfide complex (BMS) in THF, diethyl ether, or dichloromethane. Diborane reacts rapidly and quantitatively with alkenes to produce a solution of trialkylborane [16] (eq (13)). The addition of dialkylboranes. such as 9-borabicyclo[3.3.1]nonane (9-BBN. 3). disiamylborane (1), or dicyclohexylb-orane (2), to alkenes or alkynes gives mixed alkylboron compounds. The high regio-. stereo-, or chemoselectivity in the additions of these borane reagents unsaturated C—C bonds have been extensively used in organic syntheses. 

A convenient synthesis of cyclopropanol involves the reaction of propargyl bromide with 2 moles of 9-BBN in THF sodium hydroxide or methyllithium is then added. B-Cyclopropyl-9-borabicyclo[3.3.1]nonane is obtained in 70% yield. Oxidation with hydrogen peroxide (sodium acetate) in the usual way affords cyclopropanol (65% yield) and cis-cyclooctane-1,5-diol.9... 

B-bromo- or B-iodo-9-borabicyclo[3.3.1]nonanes add regioselectively to terminal alkynes to give useful intermediates for organic synthesis ... 

Synthesis of B-[Z]-l-alkenyl-9-borabicyclo[3.3.1]nonanes, not available by hydro-boration, is achieved via vinylic organolithiums ... 

A simple, convenient synthesis of B-halogeno-9-borabicyclo[3.3.1]nonane and its... 

Bis(9-borabicyclo [3.3.1]nonane) is a useful reagent for synthesis of aldehydes by carbonylation of olefins.17... 

Borabicyclo[3.3.1]nonane (9-BBN) has found use in the selective hydro-boration of alkenes in the presence of other reducible functional groups and its reaction with alkynylstannates has been studied. o-Stannyl- and a-silyl-substituted crotyl-9-BBN show promise as reagents for the stereo-regulated synthesis of acyclic systems. A series of papers covers the question of olefin-alkyl exchange in. 5-alkyl-9-BBN s, " the kinetics of reduction of substituted benzaldehydes with 9-BBN, and the kinetics and mechanism of hydroboration of alkynes with 9-BBN dimers. Selective dehalogenation of tertiary alkyl, benzyl, and allyl halides in the presence of secondary or primary alkyl or aryl halides is possible with (165). The... 

We then moved to the synthesis of the Cjj-Cig segment (Scheme 10) (29). The alcohol 53 (33) was converted to 55 by a standard C2 homologation procedure in 77% overall yield in 6 steps. Swern oxidation of 55 gave the aldehyde 56 which was submitted to Lewis acid catalyzed crotylstannylation (34). This reaction provided the expected cryfhro-adducts 57a and 57b in a 3 1 ratio which were separated by medium-pressure silica gel chromatography. Protection of 57a as a MOM ether was followed by hydroboration with 9-borabicyclo[3.3.1]nonane to afford the alcohol 58 which was further converted to the sulfone 18 by the procedure shown above. 

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