Diastereoselective Fluorocyclopropanation of Chiral Allylic Alcohols Using an α-Fluoroiodomethylzinc Carbenoid
作者:Chandrasekhar Navuluri、André B. Charette
DOI:10.1021/acs.orglett.5b02097
日期:2015.9.4
Chiral fluorocyclopropyl carbinols were synthesized in high diastereoselectivities via a zinc mediated cyclopropanation reaction, using sec-allylic alcohols as simple building blocks. An enantioselective version of this transformation was achieved through in situ formation of chiral allyliczinc sec-alkoxides from the requisite aldehydes using Walsh’s protocol.
The influence of α-coordinating groups of aldehydes on <i>E</i>/<i>Z</i>-selectivity and the use of quaternary ammonium counter ions for enhanced <i>E</i>-selectivity in the Julia–Kocienski reaction
Modified reaction conditions for improved E-selectivity of olefins in the Julia–Kocienski reaction of aldehydes having α-coordinating substituents are demonstrated. The chelating groups in aldehydes are expected to stabilize the syn-transition state with metal ions, whereas the weakly coordinating quaternary ammonium ions are devoid of all possible chelating interactions to enhance E-selectivity. A
Twoalternative and straightforward routes were developed for the construction of (R)-goniothalamin, a natural anticancer agent. The first method starts with (R)-glycidol involving stereoselective (partial) reduction of alkyne and sulfoxide Julia-Lythgoe olefination as key steps. Second method deals with the synthesis of (R)goniothalamin from 2,3-O-isopropylidene-D-glyceraldehyde with partial reduction
Alkenyl-Substituted Ketals as Efficient Precursors to Claisen Rearrangement Substrates
作者:Rebecca Cowan Hoye、Hemaka A. Rajapakse
DOI:10.1080/00397919708003340
日期:1997.2
Abstract Alkenyl-substituted ketals 6 readily afford Claisen rearrangement substrates 7 upon treatment with TESOTf/DIPEA. Thermal rearrangement completes this efficient and general process for generation of functionally rich ϵ-oxy-γ,δ-enones 8.
Olefinic diols, prepared from (R)-(+)-2,2-diinetliyl-1,3-dioxolane-4-carboxaldehyde via olefination and hydrolysis, were converted into enantiomerically pure hydroxy substituted tetrahydrofuran derivatives by cyclization using N-phenylselenophthalimide and BF3. The PhSe group in the C-4 position of these tetrahydrofurans was then substituted by an allyl group using allyl-tributylstannane in the presence of AIBN. The selenium promoted cyclizalions of the allyl tetrahydrofurans in which the OH and the allyl groups are trans to each other formed the enantiopure perhydrofuro[3,4-b]pyrans, while the cyclization of the allyl tetrahydrofurans in which the Off and the allyl groups are cis gave rise to the perhydrofuro[3,4-b]furans. These bicyclic products were finally deselenenylated with triphenyltin hydride and AIBN. (C) 2004 Elsevier Ltd. All rights reserved.