Allyl chloride hydroboration

The hydroboration of allylic chlorides provides cyclopropane derivatives when the produced organoboranes are treated with base . The simple hydroboration with... 

Hydroboration of an allylic chloride gave a cyclopropane 14 when the intermediate or-ganoborane was treated with aqueous sodium hydroxide. 9-Borabicyclo[3.3.1]nonane is particularly suitable the geometry present in the alkene is retained in the product. 3-Bromopropyne underwent reaction with two equivalents of 9-borabicyclo[3.3.1]nonane, subsequent treatment with methyllithium and then with hydrogen peroxide gave cyclopropanol. 

Synthesis of cyclopropane derivatives. The cyclization of hydroborated allylic chlorides was discovered by Hawthorne and Dupont.7 The major difficulty is that two isomeric boron derivatives are formed in roughly equal amounts, and only one is converted into a cyclopropane. Use of the more selective hydro-borating reagent disiamylborane (1, 57-59 2, 29 this volume) circumvented this... 

The synthesis of cyclopropanes from allyl chlorides, ejg. (17X via hydroboration is improved by the use of 9-borabicycIo[3,2,l]nonane (9-BBN) and is highly stereoselective. The elimination step (Scheme 1) involves inversion of configuration at the... 

The cyclization of hydroborated allylic chlorides to the corresponding cyclopropanes discovered by Hawthorne and Dont [1] is applied to the synthesis of variety of cyclopropanes [2]. However, the directive effect of chlorine directs the diborane to give roughly 50 50 of the two isomeric boron derivatives. Consequently, in such cases the maximum yield of cyclopropane derivative is not greater than 50%. 

Synthesis of PIB prepolymers. fm-Chlorine-telechelic PIB (Mn=4,000 MVf/Mn 1.09) (7), and an allyl-telechelic PIB (Mn=9,500 Mw/Mn 1.14) (7,8) were prepared by living carbocationic polymerizations. The tert-chlorine ended PIB was quantitatively dehydrochlorinated (9) to -C(CH3)=CH2 terminated polymer. Both olefin-telechelic PIBs were then hydroborated and oxidized (10) to prepare the primary hydroxyl termini. The hydroxyl-telechelic polymers were esterified with methacryloyl chloride to methacrylate-telechelic PIBs, MA-PIB-MA (11). 

By heating 32 in aqueous dimethyl sulfoxide (DMSO), containing sodium chloride, up to 170°C, loss of a methoxycarbonyl group and then -elimination of acetic acid occur to give alkene 33 in 70% yield. From this, carba-pl-L-mannopyranose 34 has been produced by conversion of the ester group to the hydroxymethyl function, hydroboration, and de-O-protection. Thus, the hydroboration step proceeded by cis-addition anti- to the allylic benzyloxy group. 

The hydroboration of acetylenes (3) with diisopinocampheylborane (IpC)2BH in THF led after refunctionalisation and transesterification to the olefins (4a, b, c) isolated in good yields. Monooxidation with mCpBA led to the sulfoxide (4d) whereas the sulfone (4e) was obtained with two equivalents of mCpBA. The same sulfone (4e) could also be obtained in an excellent overall yield by radical addition of phenylsulfonyl iodide to the pinacol ester of vinylboronic acid followed by a dehydroiodination in the presence of Et2N (87 % overall yield). The carboxylic ester (4a) could be transformed into the corresponding carboxylic acid (4f) (79 % yield) 11 which led to the acid chloride (4g) by treatment with freshly distilled thionyl chloride at 0°C (91 % yield), p-keto vinylboronates are easily accessible by oxidation of the corresponding protected allylic alcohol according to the following scheme ... 

Ring expansion with Tamura et al. s Beckmann reagent, followed by dechlorination with Zn-Cu couple in methanol saturated with ammonium chloride, provided key pyrrolidinone intermediate 197 in 72% overall yield from 193. The intermediate 197 was then converted by using selenium dioxide and tcrt-butyl hydroperoxide into allylic alcohol (62%), which yielded the desired 1,3-diol 198 through rhodium-catalyzed hydroboration and oxidation as a 1 1 mixture of diastereomers in 72% yield. A seven-step reaction sequence then converted the diol 198 into (-l-)-retronecine 199, which was indistinguishable from an authentic sample of the natural product obtained by hydrolysis of natural monocrotaline (Scheme 16.29). ... 

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