Protected functionalized alkyllithium

Anionic Synthesis of Hydroxyl-Functionalized Polymers Using Protected, Functionalized Alkyllithium and Isoprenyllithium Initiators... 

Five experimental criteria have been described for the evaluation of protected, functionalized alkyllithium initiators for anionic polymerization. Several alkoxy- and t-butyldimethylsiloxy-protected, hydroxyl-functionalized initiators have been evaluated using these criteria for the polymerization of styrene, isoprene and butadiene. All of the initiators satisfied the criteria for diene polymerization, but inefficient initiation and broader molecular weight distributions were observed for styrene polymerization, especially in cyclohexane. 

In the following sections, several protected hydroxyl-functionalized alkyllithium initiators are evaluated in terms of the criteria described for evaluation of functionalized initiators. The structures of tlie initiators and a short-hand formula description for each are shown in Scheme 2. 

The usefulness of l-alkoxy- and t-butyldimethylsiloxy-functionalized alkyllithium initiators for anionic polymerization have been evaluated using five experimental criteria. All of these criteria must be satisfied for an initiator to be generally useful. These protected hydroxyl-flmctionalized initiators are all useful for the polymerization of butadiene and styrene monomers. Inefficient initiation of styrene polymerization was observed in cyclohexane, but not in benzene. 

Quirk has recently applied that arm-first procedure to prepare functionalized star-branched PMMA using a protected hydroxy-functionalized alkyllithium initiator [58]. 

To circumvent the problems of low reactivity, low solubility, and/or low yield associated with the previously mentioned hydroxyl functional initiators, Schulz and co-workers (126) built protected-hydroxyl functionality into organolithium molecules. Specifically, alkyllithium initiators containing hydroxyl-protecting groups [mixed acetal, e.g., tetrahydro-pyranyl (22) and a-ethanoxyethyl ether (23)] have been prepared. 

The alkyllithium dehalogenation of dihalocyclopropanes can be used for derivatives having heteroatomic substituents (O, N, S) and is even compatible with alcohol functions and the preparation of allene alcohols. In the latter case two or more equivalents of the alkyllithium reagent must be used (see Table 5). Improved yields of allene alcohols can be obtained by protecting the alcohol function as the trimethylsilyl derivatives. Competing processes which can occur include C-H and O-H insertion, reductive dehalogenation and intramolecular insertion of cyclopropylidene at unsaturated sites of the substituent. 

Quantitative primary amine functionalization was obtained using these procedures (alkyllithium initiation, hydrocarbon solution, added lithium chloride) and 2,2,5,5-tetramethyl-1 - (3 -chloropropyl) -1 -aza-2,5 -disilacyclopentane (protected primary amine see Scheme 14). Terminal secondary amine-functionalized polymers have been prepared in high yield (99% for PBDLi) using N-methyl-N-benzylaminopropyl chloride as terminating agent in the presence of lithium chloride followed by hydrogenolysis of the benzyl group. ... 

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