The synthesis of the first examples of seven-membered ring iminoalditols, molecules displaying an extra hydroxymethyl substituent on their seven-membered ring compared to the previously reported polyhydroxylated azepanes, has been achieved from D-arabinose in 10 steps using RCM of a protected N-allyl-aminohexenitol as a key step. While the (2R, 3R, 4R)-2-hydroxymethyl-3,4-dihydroxy-azepane 10, a seven-membered ring analogue of fagomine, is a weak inhibitor of glycosidases, the (2R, 3R, 4R, 5S, 6S)-2-hydroxymethyl-3,4,5,6-tetrahydroxy-azepane 9 selectively inhibits green coffee bean alpha-galactosidase in the low micromolar range (Ki = 2.2 muM) despite a D-gluco relative configuration.