= Solution
\b[A is 1-propyl-1,2,4-triazole], with propyl on the nitrogen that is adjacent to one N and one C in the triazole ring, rather than on the nitrogen between the two carbon atoms.
<DBU> removes the ring NH <proton>, producing a resonance-stabilized <triazolide> anion. Nitrogen attacks the primary bromide carbon by an <SN2 reaction>, displacing bromide and giving the N-propyl product. Alkylation at the equivalent tautomer-related N1/N2 positions gives the same constitutional product, while N4 alkylation would give a different isomer. Charge distribution in the triazolide and the accessibility of its nitrogen lone pairs favor the N1 product under the stated conditions. This is kinetic <regioselectivity>, not an assertion that the unalkylated tautomer has a permanently localized negative charge.
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