Asymmetric synthesis using tartrate ester modified allylboronates. 2. Single and double asymmetric reactions with alkoxy-substituted aldehydes

Strategies to Control Alkoxy Radical-Initiated Relay Cyclizations for the Synthesis of Oxygenated Tetrahydrofuran Motifs

“…The organics were concentrated using rotary evaporation and purified by flash column chromatography (4:1 hexanes/EtOAc) to provide N-alkoxyphthalimide 42 as a colorless oil (186 mg, 69% General Procedures for Synthesis of 53. To a 0.1 M solution of sodium hydride (60% dispersion in mineral oil, 2 equiv) in dry THF at 0°C was added a 5 M solution of 1-((tert-butyldimethylsilyl)oxy)pent-4-en-2-ol (66a, P = TBS), 48 1-((tert-butyldiphenylsilyl)oxy)pent-4-en-2-ol (66a, P = TBDPS), 42 or 66b in THF dropwise over 10 min. The solution was stirred for an additional 30 min at 0°C.…”

Quantum chemical study on asymmetric allylation of benzaldehyde in the presence of chiral allylboronate

“…However, the reaction mechanism has rarely been reported owing to its complexity. Roush hypothesized a transition state structure of the asymmetric allylation (Roush et al, 1990b), and successfully explained the corresponding relationship of experimental results and product structures. Gung et al(2002) suggested that n/n electronic repulsion plays only a minor role in stereodifferentiation in the allylboration reaction based on the fact that distances between the aldehydic hydrogen and the carbonyl oxygen in the transtition structure and between the aldehydic oxygen and the amide carbonyl oxygen exceed the sum of van der waals radii.…”

“…From the computational results we know that the bonds of C2-C6 and O3-B9 are formed at the same time to Table 1 Selected bonds lengths (nm) and bonds angles (°) consist of a six-membered ring transition state structure. Roush et al(1990b) hypothesized that the allylation can be accomplished through a six-membered ring chair-like transition state structure. We were able to obtain both of chair and boat-twist transition structures after optimization with OPT=QST3 on B3LYP/ 6-31G(d,p), and which confirmed later by vibrational analysis with Freq (Noraman) at the same level (Fig.3).…”

Allylation of Aldehyde and Imine Substrates with in situ Generated Allylboronates — A Simple Route to Enantioenriched Homoallyl Alcohols.

“…[1][2][3][4][5] Furthermore, tartrate based chiral allylboronates react with aldehydes with good to high level of enantioselectivity. [4,6,7] Although, the parent allylboronate and its alkyl-substituted analogs are easily available reagents, the limited access to properly functionalized and/or chiral allylboronates often limit the synthetic scope of the allylation reactions. Recently, we have communicated [8] an efficient one-pot allylation procedure based on in situ generation of allylboronates (Scheme 1).…”