B-C1-9-BBN

Similarly, the B-C1-9-BBN derivative also forms a 1 1 complex with pyridine and gives separate signals for syn and anti halves (relative to pyridine [Py]) of... 

The literature describes number of methods for the generation of enolborinates [1]. Enolborinates are valuable intermediates [2] and react with high stereospecificity in aldol condensation [3-8]. Brown and coworkers [9] have carried out a detailed study of the stereochemistry of ketone enolization with B-C1-9-BBN [10], B-OTf-9-BBN [3c], Chx BCl [10], and ChXjBOTf [9] to get ( )- or (Z)-enolborinates. It is found that stereochemical outcome of the reaction varies not only with the steric requirements of RjB and steric requirements of the amine [4, 5b, c], but also with the nature of the leaving group. Cl or OTf (Table 20.1) [9]. 

The effects of varying the amine and alkyl groups on boron are more significant in the case of R BCl than in the case of RjBOTf, and quantitative synthesis of (Z)-enolborinate has been achieved using l-PrjEtN and B-C1-9-BBN, whereas enolization with Chx BCl and amine EtjN gives (E)-enolborinate (Scheme 20.1 Table 20.2) [9], almost exclusively. 

Both ChXjBCl and B-C1-9-BBN are obtained from the corresponding or-ganoborane and anhyd HCl in ether [7a]. 

The B-alkyl, alkenyl, alkynyl, or aryl-9-BBN derivatives not available via hydroboration are obtained by alkylation of 9-BBN or B-C1-9-BBN or B-MeO-9-BBN with organolithium, Grignard reagent, organocadmium, lithium dialkylcuprates, (phenylthio)alkylcuprates, andhydroboration-carbonylation-reduction. 

The results of alkylation of B-C1-9-BBN with organolithiums are summarized in Table 23.2 [1]. 

The general reactivity order for haloboration reagents is shown in Schane 23.32 B-C1-9-BBN is very inert as a haloborating agent. 

B-I-9-BBN, BBi3 > BCI3 > B-Br-9-BBN B-C1-9-BBN SCHEME 23.32 Reactivity order for haloboration reagents. 

Organoborane R3B or B-R-9-BBN Chloronitrile CI2CHCN or RCH(C1)CN Reaction conditions Temp Time ( O (h) Product Yield (%)... 

B. Techniques. The synthesis and purification of a, u)-di (tejrt.-chloro ) poly isobutylene C1-PIB-C1 (formula I in Scheme I) and the preparation of ct, io-di ( isobut-enyl)polyisobutylene (formula II in Scheme I) by quantitative regioselective dehydrochlorination of Cl-PIB-C1 have been described [1,3]. Details of the synthesis of a, u-di (hydroxy)polyisobutylenes HO-CH2-PIB-CH2-OH (formula IV in Scheme I) by hydroborations of ct,w-di-( isobutenyl)polyisobutylene with 9-BBN or BH3 THF, have been given elsewhere [4]. 

---