Borane anions alkylation

If boranes (K. Utimoto, 1973 H.C. Brown, 1975, 1980 A. Pelter, 1979) are used as donor synthons for the alkylation of a, -unsatarated carbonyl compounds, no enolate anion is formed, and the, 8-position of the C=C bond is the only reaction site. 

A radical initiator based on the oxidation adduct of an alkyl-9-BBN (47) has been utilized to produce poly(methylmethacrylate) (48) (Fig. 31) from methylmethacrylate monomer by a living anionic polymerization route that does not require the mediation of a metal catalyst. The relatively broad molecular weight distribution (PDI = (MJM ) 2.5) compared with those in living anionic polymerization cases was attributed to the slow initiation of the polymerization.69 A similar radical polymerization route aided by 47 was utilized in the synthesis of functionalized syndiotactic polystyrene (PS) polymers by the copolymerization of styrene.70 The borane groups in the functionalized syndiotactic polystyrenes were transformed into free-radical initiators for the in situ free-radical graft polymerization to prepare s-PS-g-PMMA graft copolymers. 

Advances in the use of anionic stereogenic phosphorus have been interesting. Acylation of lithium o-anisylphenylphosphide with chloro-formates bearing chiral alkyl groups provided a diastereomeric mixture that could be induced to undergo an inversion at phosphorus (at relatively low temperature) to form the more favorable diastereoisomer in a crystalline lattice.186 Subsequent conversion to the quaternary phos-phonium species was followed by removal of the acyl group and isolation of the chiral tertiary phosphine as the borane derivative (Equation 3.10). 

For a review of anions a lo a selenium atom on small rings, see Krief Top. Curr. Chem. 1987, 135. 1-75. For alkylation a to boron, see Pelter Smith Brown Borane Reagents, Academic Press New York, 1988, pp. 336-341. 

Lithioferrocene (322) or dilithioferrocene (323) can also be prepared, and then utilized in situ, from the corresponding halo- or dihaloferrocenes by halogen-metal exchange with alkyl lithiums. Alternatively, monohthiation of l,l -dibromoferrocene gives rise to anion (351), which may be reacted with an electrophile in order to afford additional ferrocene derivatives. In this way, monophosphine oxazoline ferrocene (340) is prepared from bromo oxazoline ferrocene (352), a compound that also is used to prepare chiral-at-phosphorus ferrocenes (353). Other chiral-at-phosphoras ferrocenes (354) are made from (323) and a phosphite borane as the electrophile (equation 80). The phosphorus atoms may also be contained in a ring that possesses chirality the sequences used to prepare this family... 

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