Hidetaka Yatagai

Stereo- and regiocontrol of acyclic systems via the lewis acid mediated reaction of allylic stannanes with aldehydes

Abstract The reaction of crotyltrialkylstannanes (1) with aldehydes in the presence of BF3,OEt2, produces the corresponding erythro homoallyl alcohols (2) predominantly regardless of the geometry of the double bond. Further, the Lewis acid mediated reaction exhibits the enhanced Cram selectivity in comparison with other allylic organometallic reactions which proceed in the absence of Lewis acids. Use of AlCl3-i-PrOH as the Lewis acid entirely changes the reaction course; the linear adduct (12) is produced rather than the branched adduct (13). The reaction of 1-BF3,OEt2 system is applied to the short and stereoselective synthesis of the (±) Prelog-Djerassi lactonic acid (16) and (-) verrucarinolactone (19).

Threo-selective aldol condensations of lithium enolates in the presence of trialkylboranes

Abstract The reaction of preformed lithium enolates in the presence of trialkylboranes, such as Et 2 B and n-Bu 3 B, with aldehydes leads to product mixtures rich in the more stable threo aldol.

13C NMR spectra of allylic boron “ate” complexes. Relative importance of σ-π conjugation between the double bond and the carbon-boron bond

Abstract Carbon-13 NMR spectra of allylic boron “ate” complexes clearly indicate, for the first time, the relative importance of σ-π conjugation between the double bond and the carbon-boron bond.

Enhancement of threo-selectivity in the reaction of but-2-enyl-lithium with aldehydes via allylic boronate complexes

The threo-selectivity of the reaction of but-2-enyl-lithium with aldehydes in the presence of certain trialkylboranes is enhanced; the corresponding allylic boronate complexes are presumably involved as intermediates.

RhCl3-catalysed amide bond formation under mild conditions

The reaction of carboxylic acid esters with amines is accelerated in the presence of catalytic amounts of RhCl3.3H2O at a reasonably low temperature; optically active 2,5-dioxopiperazines can be synthesized in high yield from the corresponding amino-acid esters using this procedure.

erythro-Selective aldol condensation via triphenyltin enolates. Stereoselection independent of the stereochemistry of the enolates

Triphenyltin enolates, prepared from lithium enolates and triphenyltin chloride, undergo a rapid aldol condensation with aldehydes without the need for the presence of Lewis acids to give predominantly the erythro-product regardless of the geometry of the starting enolates.

Regiocontrolled head-to-tail coupling of alkylthioallyl carbanions with allylic halides via lithium alkylthioallyl borates

Reaction of lithium alkylthioallyl borates (3), prepared from alkylthioallyl-lithium (1) and trialkylboranes at –78 °C, with allylic halides (2) gives head-to-tail 1,5-dienes (4) in good yields.

Protonolysis of alkenylboranes under neutral condition by treatment with catalytic amounts of palladium diacetate

Alkenyldialkylboranes (1) from internal alkynes undergo easy protonolysis by catalytic amounts of Pd-(OAc)2 to give the corresponding (Z)-olefins (2) in good yields.

Stereoselective synthesis of E-olefins by the reaction of alkenylboranes with palladium acetate

Alkenyldialkylboranes (1) react smoothly at room temperature with Pd(OAc)2–Et3N to produce E-olefins (2) stereoselectively in moderate to high yields.

Stereoselective synthesis of 1,4-dienes and mono-olefins by methylcopper-induced cross-coupling of dialkenylchloroboranes with organic halides

Mono-olefins and 1,4-dienes have been synthesised with >99% stereochemical purity by the methylcopper-induced cross-coupling of dialkenylchloroboranes, formed from alkynes, with organic halides.