9-BBN allyl

In contrast to ordinary chiral aldehydes (having no ability to be chelated), the reaction of 9-allyl-9-borabicyclo[3.3.1]nonane(allyl-9-BBN) with the corresponding chiral imines 4 produces the isomer syn-6 either exclusively or predominantly (Cram selectivity Table 8)5,6. The very high 1,2-asymmetric induction is explained by a six-membered. chair-like transition state, in which the inline R group occupies an axial position due to the stereoelectronic effect of imines (R CH = NR). 

The reaction of allyl-9-BBN with the chiral imine 1 gives the Cram isomer 2 predominantly5,6. The 1,3-asymmetric induction is developed by a transition state 3, in which the 1,2-axial-equa-torial interaction between R and the ligand (L) plays an important role in the high chiral induction. 

Allylic boranes such as 9-allyl-9-BBN react with aldehydes and ketones to give allylic carbinols. The reaction begins by Lewis acid-base coordination at the carbonyl oxygen, which both increases the electrophilicity of the carbonyl group and weakens the C-B bond to the allyl group. The dipolar adduct then reacts through a cyclic TS. Bond formation takes place at the 7-carbon of the allyl group and the double bond shifts.36 After the reaction is complete, the carbinol product is liberated from the borinate ester by displacement with ethanolamine. Yields for a series of aldehydes and ketones were usually above 90% for 9-allyl-9-BBN. 

Nucleophilic Addition by Allylboron Derivatives. Allylboranes such as 9-allyl-9-BBN react with aldehydes and ketones to give allylic carbinols. Bond formation takes place at the y carbon of the allyl group, and the double bond shifts.33... 

Block copolymers can be produced from terminally borane-containing polyolefins. These borane-containing POs can be synthesized by the metallocene-catalyzed (co)polymerization of olefin(s) monomer with 9-BBN as a chain transfer agent or by the metallocene catalyzed copolymerization of olefins with allyl-9-BBN [55,56], as referred to above. Alternatively, borane-containing POs were prepared by hydroboration of terminally unsaturated PO, for instance, terminally vinyl PE and terminally vinylidene PP [33-35,57]. Such method could produce diblock copolymers, such as polyethylene-block-poly(methyl methacrylate) (PE-fo-PMMA), polypropylene-foZock-poly(methyl methacrylate) (PP-fc-PMMA), polypropylene-foZock-poly(butyl methacrylate) (PP-fc-PBMA), and PP-fc-PS. 

S-Allyl-9-BBN is prepared by the addition of an aluminium derivative of allyl bromide to B-methoxy-9-BBN. 

Although the first two additions proceed under relatively mild conditions, temperatures of over 100 °C are required to effect the third addition, and so 9-BBN derivatives often prove convenient substrates for the reaction. An example of the use of B-allyl-9-BBN is depicted in Equation B5.1. 

Less is known about the reactions of allylboron compounds however, an ate complex between B-allyl-9-BBN and NaOMe afforded allylarenes in high yields within 0.5-1 h (Equation (209)).898... 

B-allyl-9-BBN reacts vigorously with acid chlorides and acid anhydrides slowly with carboxylic acid esters and N,N-dimethylbenzamide (Eq. 47)98). 

Hydroboration of allenes. With few exceptions, the 9-BBN hydroboration of allenes affords B-allylic-9-BBN derivatives. In contrast, the reactions of allenes with disiamylborane or dicyclohexylborane afiord predominantly vinylic boranes. With unsymmetrical allenes, 9-BBN binds to the less substituted carbon atom. Allene itself affords a 1,3-dibora derivative. The B-allylic-9-BBN derivatives are useful reagents for the allylic boration of carbonyl compounds. ... 

Allylic-9-BBN derivatives are also available by hydroboration of allenes with 9-BBN-H. Unlike disiamylborane, 9-BBN-H shows a marked preference for attachment of boron to one of the termini of the allene system rather than to the central carbon atom. Allene itself is dihydroborated by 9-BBN-H, but substituted allenes give rise predominantly to allylboranes (e.g. equation 34). ... 

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%). 

In contrast to HjB-THF and other dialkylboranes, 9-BBN shows a strong tendency to form B-allylic-9-BBN derivatives in the hydroboration of aliphatic allenes. This tendency is retained even when the allene system is unfavorably substituted. Lower selectivity may be expected for cyclic allenes, for 1,2-cyclononadiene gives 17% of B-cyclononen-l-yl-9-BBN and 83% of B-cyclononen-2-yl-9-BBN. The reaction can be... 

Although (7) reacts with trimethylsilyl chloride (TMS-Cl) at the 7-position because of the steric bulk of the siamyl group, the 9-borabicyclo[3.3.1]nonyl (9-BBN) derivative (equation 1) gives the a-tri-methylsilyl or a-trimethylstannyl allylic-9-BBN upon treatment with TMS-Cl or trimethyltin chloride. ... 

Insight into the structure of several allyl/crotyl organometallic reagents has been obtained spectroscopically. Kramer and Brown have examined the NMR spectra of 3-allyl-9-BBN and 3-crotyl-9-BBN... 

Figure 2 P-Allyl-9-BBN exists in a state of permanent allylic rearrangement ...

In all cases, allyl-9-BBN provides the best diastereoselectivity. The high 1,3-asymmetric induction (96 4) produced in allyl-9-BBN addition to (36 R = Ph entry 1, Table 9) is consistent with a proposed cyclic chair transition state shown in Figure 11a. Diastereofacial selectivity is reversed in methallyl-9-BBN addition to (36 R = Ph entry 3, Table 9). As a result of additional 1,3-diaxial interactions invol-... 

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