We began our investigation with enaminone 1a and 1.4 equiv
of LDA (lithium diisopropylamide) using a lithiation temperature
of −78 °C under a N2 atmosphere, followed by adding 1.5
equiv of 4-bromobenzaldehyde 2a. 3-Amino furan 3a was
efficiently obtained in 80% isolated yield (Table 1, entry 1). To our delight, no α-lithiation byproduct was detected. This result
encouraged us to optimize the reaction conditions with 1a and
2a as model substrates (Table 1). First, LDA was tested in situ,
and almost no difference in product yields was observed
(entries 1 and 2). Because LDA is commercially available, we
chose to use LDA as the organolithium reagent. When the
lithiation temperature was increased to −40 °C, the yield of
desired product 3a decreased to 66% (entry 3). Next, the
lithiation temperature was fixed at −78 °C and the amounts of
LDA and 4-bromobenzaldehyde 2a were screened, revealing
that 2.0 equiv of LDA and 2a was essential to this system, with
85% isolated yield of 3-amino furan 3a (entries 4−7).