Scope of DA reaction between 2-furoic acid derivatives (esters, amides) and maleimides under aqueous conditions.

Entry	X	R2	3	Conv. 1a	exo-3, %	endo-3, %	Isolatedb, %
1	OMe	Me	3k	70	65	5	52(74)
2	OMe	H	3l	67	65	2	43(64)/82c
3	OMe	Et	3m	65	61	4	47(72)
4	OEt	Me	3n	63	59	4	29(46)
5	OiPr	Me	3o	54	50	4	26(49)
6	OtBu	Me	3p	54	51	3	25(46)
7	NH2	Me	3q	94	91	3	77(83)
8	NMe2	Me	3r	81	77	4	41(51)
9	NHOH	Me	3s	92	76	16	69(75)

^aConversion determined from the ¹H-NMR ratios of product isomers and starting material.

^bIsolated yield after (chromatographic) workup (in brackets, yield corrected on reacted starting material).

^c2 M initial concentration.