Table 2.

Synthesis of furan-bearing α-amino esters by a [2 + 4] cycloaddition.

Ar	R1	R2	% 2a	% 1a
ae	H	H	–	–
af	Me	H	42b/41c/50d	–
ag	Me	Me	38b/48c/50e	–
ah	Et	H	43b	–
am	n-Pr	H	40b	79
an	n-pentyl	H	32c	90
ao	Me	Et	21c,f	82
ap	(CH2)4		40b,g	82
aq	Et	Me	25c, h	90
ar	iPr	Me	30c,i	86

^aIsolated yield. ^bToluene, NBu₄Br (cat.), Na₂CO₃. ^cH₂O/AcOEt, NH₃/HCO₃H. ^dH₂O/AcOEt, Li₂CO₃. ^eH₂O/AcOEt, Na₂CO₃. ^fOverall yield from 1-(2-methylfuran-3-yl)ethan-1-one. ^gOverall yield from 6,7-dihydrobenzofuran-4(5H)-one. ^hOverall yield from ethyl 2-ethylfuran-3-carboxylate. ⁱOverall yield from ethyl 2-isopropylfuran-3-carboxylate.