(5E)-Dimethyl 2-bromo­methyl-5-cyclo­hexyl­imino-2-phenyl-2,5-dihydro­furan-3,4-dicarboxyl­ate

The mol­ecule of the title compound, C21H24BrNO5, has a planar furan ring [maximum deviation = 0.025 (3) Å]. The carboxy­methyl group in the 3-position is nearly coplanar with this ring [dihedral angle = 7.9 (1)°], whereas that in the 4-position is nearly perpendicular to it [dihedral angle = 78.9 (1) Å]

1-(2-Eth­oxy-2-methyl-2H-chromen-3-yl)ethanone

The Csp 3 atom of the chromenyl fused-ring system in the title compound, C14H16O3, deviates by 0.407 (2) Å from the plane of the other atoms (r.m.s. deviation = 0.041 Å). The eth­oxy substituent occupies a pseudo-axial position

A Systematic Study of the Effects of Relative Configuration, Protecting Group, and Enolate Type on the Diastereoselectivities of Aldol Reactions of a Chiral Ethyl Ketone with 2‑Methylpropanal

The diastereoselectivities of aldol reactions of 2-methylpropanal with various enolates of 5-<i>O</i>-methoxymethyl and 5-<i>O</i>-triethylsilyl derivatives of the four racemic diastereomers of 6-(2-ethyl-1,3-dioxolan-2-yl)-5-hydroxy-4-methylheptan-3-one are reported. Reactions of the (<i>E</i>)-enol dicyclohexylborinates, (<i>Z</i>)-enol 9-BBN borinates (i.e., 9-((<i>Z</i>)-enoxy)-9-borabicyclo­[3.3.1]­nonanes), Li (<i>E</i>)-enolates, Li (<i>Z</i>)-enolates, and Ti­(IV) (<i>Z</i>)-enolates were examined. Boron and Li enolates were prepared by standard methods, but Ti­(IV) enolates were obtained via transmetalation of the Li (<i>Z</i>)-enolates by reaction with TiCl_<i>n</i>(O<i>i</i>-Pr)_4–<i>n</i> (<i>n</i> = 0–2). Aldol relative topicity (simple diastereoselectivity) was strongly correlated to the enolate geometry: <i>anti</i> aldols from (<i>E</i>)-enolates and <i>syn</i> aldols from (<i>Z</i>)-enolates. However, for each enolate type, the diastereoface selectivities varied widely (by factors of 5–400) with the relative configuration and nature of the C5 protecting group in the 8 starting ketones. Plausible transition state models are postulated to rationalize some of these observations. The relative configurations for the complete set of 16 diastereomeric 2-(2-ethyl-1,3-dioxolan-2-yl)-7-hydroxy-3-(methoxymethoxy)-4,6,8-trimethylnonan-5-one aldol adducts were confirmed by NMR analysis of 12 acetonide derivatives prepared from the corresponding 5,7-<i>syn</i> diols. Examination of the NMR data for the above set of aldol adducts revealed consistent trends that were exploited to assign the relative configurations of 13 diastereomeric 2-(2-ethyl-1,3-dioxolan-2-yl)-7-hydroxy-3-(triethylsilyloxy)-4,6,8-trimethylnonan-5-one aldol adducts