Alkylation of n-butane

Recently, Nicolaou et al.167) reported an elegant asymmetric synthesis of the ionophore antibiotic X-14547 A (153) isolated at Hoffmann-La Roche from Strepto-myces antibioticus NRRL 8167. The key step in this synthesis was an enantioselective a-alkylation of n-butanal via its SAMP-hydrazone (151) to produce the intermediate (152). The asymmetric induction as determined by NMR-spectra of the product SAMP-hydrazone, was 95 % e.e. 

Alkylation of n-butane and isobutanc with methyl or ethyl bromide in the presence of aluminum bromide has been claimed (Heldman, 36). It was found, for example, that the action of aluminum bromide (0.00158 mole as Al2Br ) on a solution of 0.0392 mole methyl bromide in 0.0750 mole n-butane at 25° for 120 hours yielded 0.0052 mole isopentane (13% of the theoretical based on the methyl bromide) isobutane was also formed. In a similar experiment carried out at 78° for 65 hours, the yield of isopentane was 33%. The reaction of isobutane (0.0520 mole) with methyl bromide (0.0392 mole) in the presence of aluminum bromide (0.00142 mole AUBrj) at 25° for 283 hours yielded low boiling material (0.0009 mole), n-butane (0.0062 mole), unreacted isobutane (0.0410, 79% of that charged), isopentane (0.0034 mole, 9% of the theory) and higher boiling material (0.0024 mole). 

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