Studies toward Soraphen A: An Aldol−Metathesis Avenue to the Macrocyclic Framework
摘要:
We describe a convergent approach to soraphen A, 1, that involves coupling of two fragments by an aldol condensation - olefin metathesis sequence. This route permits rapid access to congeners of 1.
4,5-Diisopropyl-B-[(E)-[(3‘-menthofuryl)dimethylsilyl]allyl]-1,3,2- dioxaborolane, an Improved Chiral Reagent for the Anti α-Hydroxyallylation of Aldehydes: Application to the Enantioselective Synthesis of (−)-Swainsonine
摘要:
Diisopropyl tartrate-modified (E)-[gamma-(furyldimethylsilyl)allyl]boronates 10 and 11 were designed for the enantioselective synthesis of substituted anti-3,4-dihydroxy-1-butenes 9 via the anti-alpha-hydroxyallylation of aldehydes. The reactions of aldehydes with 10 and 11 provided furyldimethylsilyl-substituted anti-1,2-silanols 12 and 13 with good enantioselectivity (74-82% ee), and the silanols were oxidized to the corresponding anti-1,2-diols 9 by a modified Fleming-Tamao oxidation protocol. The high reactivity of the (menthofuryl)silane unit toward electrophilic substitution allowed complete protodesilylation of menthofuryl-substituted silanols 13 and subsequent oxidation to diols 9 in a one-pot operation without competing protodesilylation of the allylsilane unit. However, a two-step protocol was required for the protodesilylation-oxidation of the less reactive 2-(5-methyl)-asymmetric reactions with three chiral aldehydes 23-35 (80 to >92% de, with the exception of the mismatched reactions with aldehyde 25, which were essentially unselective). However, [[[2-(5-methylfuryl)]dimethylsilyl]ally]boronate 10 could only be synthesized in less than or equal to 15% yield, and oxidations of the 2-(5-methylfuryl)-substituted silanols 12 were lower-yielding than oxidations of the corresponding menthofuryl-substituted silanols 13. Thus diisopropyl tartrate-modified (E)-[gamma-[(menthofuryl)dimethylsilyl]ally]boronate 11 proved to be the more useful of the two reagents. As a demonstration of the utility of 11 in the synthesis of polyhydroxylated natural products, this new reagent was used in a brief and highly stereoselective synthesis of the naturally occurring alkaloid (-)-swainsonine (42).
Diisopropyl tartrate modified (E)-γ-[(cyclohexyloxy)dimethylsilyl-allylboronate, a chiral reagent for the stereoselective synthesis of anti 1,2-diols via the formal α-hydroxyallylation of aldehydes
作者:William R. Roush、Paul T. Gover、Xiaofa Lin
DOI:10.1016/s0040-4039(00)97299-x
日期:1990.1
An enantioselective synthesis of anti 1,2-diols via the reactions of aldehydes and the tartrateestermodified γ(alkoxysilyl)allylboronate2 has been developed. This method is most effective in double asymmetric reactions with chiral aldehydes.
The study of intramolecular tandem radical cyclizations of acylsilanes with radicalphiles attached on silicon
作者:Kuo-Hsiang Tang、Fang-Yu Liao、Yeun-Min Tsai
DOI:10.1016/j.tet.2004.12.053
日期:2005.2
Radicalcyclizations of acylsilanes with radicalphilic pendant introduced on silicon proceeded in a tandem fashion to give spiro products containing a cyclic silyl ether skeleton. Because the alkoxysilyl group can be replaced with a hydroxy group through oxidation, the spiro silyl ethers can be converted into diols. In the case with a radical intermediate carrying 2-oxa-3-sila-6-heptenyl skeleton,
Group transfer from silicon to carbon via tandem radical cyclizations of acylsilanes
作者:Yeun-Min Tsai、Kuo-Hsiang Tang、Weir-Torn Jiaang
DOI:10.1016/0040-4039(96)01773-x
日期:1996.10
Tandem radical cyclizations of acylsilanes with alkene or alkyne functionalities attached to silicon afforded cyclic silyl ethers which were oxidatively hydrolyzed to give diols or ketone alcohols.