Borane dimethylsulfide complex

B. (Z)-l-Iodo-l-heptene.2 A solution of 8.52 g of (112 mmol) of borane-dimethylsulfide complex (Note 13) in 100 mL of ether is added to a flame-dried, three-necked, 300-mL, round-bottomed flask equipped with stirbar, temperature probe, and N2 inlet. The solution is cooled to 5°C with an ice-bath. Cyclohexene (18.4 g, 224 mmol) (Note 14) is then added by syringe over 10 min while keeping the temperature below 15°C. The mixture is stirred at 5°C for 15 min. A white solid precipitates either towards the end of the addition or during the subsequent stirring period. The reaction mixture is allowed to warm to room temperature and is stirred for 1 hr. The non-homogeneous solution is cooled to 2-3°C... 

M Borane-dimethylsulfide complex (2.0 mL) was added to the resulting solution. The mixture was cooled to 0-5 °C with an ice-bath, and then a solution of 2,3-butadione monoxime trityl ether (1.72 g) in dry tetrahydrofuran (5 mL) was added dropwise via a syringe pump over 1 hour at that temperature. 

SYNTHESIS A solution of 5.50 g 2,5-dimethoxy-4-ethylthio-B-nitrostyrene (see under 2C-T-2 for its preparation) was made in 80 mL boiling anhydrous THF. On cooling, there was some separation of a fine crystalline phase, which was kept dispersed by continuous stirring. Under an inert atmosphere there was added 3.5 mL of a 10 M borane dimethylsulfide complex, followed by 0.5 g sodium borohydride as a solid. There was a slight exothermic response, and the color slowly faded. Stirring was continued for a week. There was then added 40 mL H,0 and 20 mL... 

Hydroboration-oxidation of enecarbamates with borane-dimethylsulfide complex gives reasonable yields of /i-hydn > xycarbarn ales (equation 28) with some diastereoselectivity, depending upon what other functional groups are present in the starting material152. 

The benzoyl groups of 43 were reduced using a borane-dimethylsulfide complex to give the corresponding iV-benzy 1 -diazocinc 44, which, upon hydrogenolysis with 20% Pd(OH)2 followed by acid hydrolysis, afforded the NH diazocine 30 (R = H) (Scheme 10) <1998CPB674>. 

Nitro-4-(trifluoromethyl)-phenol 42 (Scheme 17) in reaction with 2-bromo-2-methyl-propionamide in the presence of cesium carbonate and cesium iodide in acetonitrile afforded 2-hydroxy-2-methylpropionamide 43, apparently via derivative 44 as the intermediate [32]. Amide 44, prepared on a circuitous route, on reduction with borane-dimethylsulfide complex, gave amine 45 as the only isolated product. The parent 2-hydroxy-2-methyl-W-(2-... 

E.J. Corey and co-workers synthesized the cdc25A protein phosphatase inhibitor dysidiolide enantioselectively. In the last phase of the total synthesis, the secondary alcohol functionality of the side-chain was established with a highly diastereoselective oxazaborolidine-catalyzed reduction using borane-dimethylsulfide complex in the presence of the (S)-6-methyl CBS catalyst. Finally, a photochemical oxidation generated the y-hydroxybutenolide functionality. This total synthesis confirmed the absolute stereochemistry of dysidiolide. 

An analogous approach was used in a stereoselective synthesis of /Tamino-a-hydroxy phosphonates [33]. Reduction of corresponding a-keto phosphonate substrates with borane-dimethylsulfide complex aided by oxazaborolidine catalysis afforded a mixture of diastereomers, but significant diastereoselectiv-ity was achieved using catecholborane as the reductant in toluene at -60 °C. 

The preparation of each is easy and this is the route to 87/88 as described by Evans11 in Organic Syntheses. Reduction of the free acid 91 with the borane-dimethylsulfide complex is easy if smelly and the rest is straightforward. The same auxiliary 87 can be used with any acid acylation with the acid chloride gives the chiral derivative 93 ready for enolate formation. 

Segment Cl was synthesized from (tf)-malic acid as a starting material in the following three steps (Scheme 27) (I) diesterification with acetyl chloride in methanol, (II) selective reduction of a-hydroxy ester with boran dimethylsulfide complex and sodium borohydride in THF, and (III) acid catalyzed lactonization of 145 (90). 

Treating diethyl (-h )-(i ,i )-tartrate (lb) with triethyl orthoacetate under acidic conditions provides the cyclic orthoester 530, which is then ring opened with acid to afford the monoacetate 531 in 94% overall yield. Protection of the free hydroxyl group followed by basic hydrolysis of the acetate furnishes 532. The regioselective reduction of 532 with borane-dimethylsulfide complex and a catalytic amount of sodium borohydride followed by acetonide... 

Regioselective reduction of the a-hydroxy ester group in 822 to the highly labile dihydroxy azido ester 829 is accomplished with borane-dimethylsulfide complex and a catalytic amount of sodium borohydride. Immediate treatment of 829 with dimethoxypropane affords the isolable ethyl 2-azido-3,4-(9-isopropylidene-3,4-dihydroxybutanoate (830) in 59% yield for the two steps. Subsequent catalytic reduction of the azido group followed by either N-Boc or N-Cbz protection provides either 831 or 832 in excellent yield. These are equivalent to e /iro- -hydroxymethyl-L-serine. The enantiomeric 833 and 834 are readily available from diethyl D-tartrate through a similar series of transformations [239] (Scheme 182). 

One of the most potent frameworks for the synthesis of two contiguous stereochemically defined asymmetric centers is the chiral epoxy functionality. Prepared in molar-scale quantity from dimethyl L-tartrate (la), bromohydrin 860 is a shelf-storable solid that undergoes selective reduction at the a-hydroxy ester function with borane-dimethylsulfide complex in the presence of catalytic sodium borohydride to provide a 4 1 mixture of methyl (2S,3S)-2-bromo-3,4-dihydroxybutanoate (861) and methyl (2i, 3i )-3-bromo-2,4-dihydroxybutanoate (862). Without purification this mixture is treated with ert-butyldimethylsilylchloride and then exposed to sodium methoxide, which results in conversion to the single epoxide methyl (2i, 3iS)-4-( err-butyldimethylsilyloxy)-2,3-epoxybutanoate (863) in 95% yield and with 99% optical purity (Scheme 188). 

Nucleophilic attack at other atoms. The chemistry of phosphine-borane adducts has continued to generate interest. Simple borane adducts of primary vinyl-, ethynyl- and allenyl-phosphines have been prepared and studied by a range of spectroscopic and theoretical techniques. The same group has also shown that attachment of the BH3 unit to a variety of primary phosphines results in a substantial increase in the intrinsic acidity of the system in the gas-phase. Group III halide adducts of the type Bu 2PH EX3 (E = B, Al, Ga or In X = Cl or Br) are accessible from the reactions of the secondary phosphine with the trihalides at room temperature. The solid state structure and reactivity of these adducts was also reported. Treatment of l,8-bis(diphenylphosphino)naphthalene with the borane-dimethylsulfide complex in ether solvents affords a simple monoborane adduct of the diphosphine irrespective of the molar ratio of the... 

For the second building block for verrucarin A (380), a derivative of verrucarinic acid (465) was synthesized in enantiomerically pure form from diester 461. Cleavage with pig liver esterase led to monoester 462, which was reduced to the alcohol with borane dimethylsulfide complex and protected with TBSCl to obtain the molecule 463. a-Hydroxylation with molybdenum oxide generated alcohol 464, and final protection and saponification afforded compound 465 (Scheme 8.16). 

The regioselective reductive-cleavage of the galactose-glucose link in die sialic acid containing trisaccharide derivative 7 with borane-dimethylsulfide complex in the presence of boron trifluoride or by triethylsilane afforded anhydro derivative 8."... 

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