Pronounced Electronic Effect of Allylic Amino Groups on the π‐Facial Stereoselectivity and Reactivity of the Iodoetherification of N ‐Substituted 3‐Amino‐4‐penten‐1‐ols

The iodoetherification of N ‐substituted 3‐amino‐4‐penten‐1‐ol ( 1 ) [I 2 and NaHCO 3 (2 equivalents each) in ether/H 2 O at 0°C], providin the mixtures of N ‐substituted cis ‐ and trans ‐ 3‐amino‐2‐iodomethyltetrahydrofurans ( 9 ), displayed diastereoselectivity which was found to correlate with the Taft σ * constants of the N ‐substitutents (SO 2 CF 3 , SO 2 Me, SO 2 ‐ P ‐Tol, COPh, COMe): log( cis ‐ 9 / trans ‐ 9 ) = 0.616σ * – 1.67 ( r = 0.997). the 2‐methyl‐substituted derivatives of 1 exhibit larger ρ values, while for the 4‐methyl derivative of 1 is approximately zero, Iodoetherification of a variety of N ‐tosyl (σ * = 3.32) 1‐ and 2‐substituted derivatives of 1 afforded the corresponding cis isomers with 70 – >95% selectivities, while that of the N ‐benzoyl (σ * = 2.20) derivatives furnished the trans isomeres with 70–80% selectivities. These results are interpreted in terms of a π C(4)–C(5) ‐σ * C(3)–N interaction of conformer II . The N ‐CO 2 R (R = Et, t ‐Bu) and N ‐SO 2 NMe 2 derivatives of 1 display anomalously high cis selectivities.