(Z)-.alpha.-(trimethylsilyl) .alpha.,.beta.-unsaturated esters. Their stereoselective conversion into .alpha.,.beta.- and .beta.,.gamma.-unsaturated esters and .beta.,.gamma.-unsaturated ketene acetals
摘要:
Deprotonation of methyl (Z)-alpha-(trimethylsilyl) alpha,beta-unsaturated esters with lithium diisopropylamide (LDA) or with lithium hexamethyldisilazide (LHMDS) in the presence of hexamethylphosphoramide (HMPA) as an activator, followed by protonation of the intermediate dienolates with methanol, produces stereoselectively the desilylated (E)-3-alkenoic esters. Trapping the dienolates with chlorotrimethylsilane instead of methanol and then treatment of the resultant ketene acetals with aqueous hydrochloric acid affords (E)-alpha-(trimethylsilyl)-beta,gamma-alkenoic esters in 98% isomeric purities. In the absence of HMPA, (Z)-alpha-(trimethylsilyl)-alpha, beta-alkenoic esters undergo a Michael-type addition with LDA to furnish, after methanol-mediated elimination of the diisopropylamine moiety, (E)-alpha-(trimethylsilyl)-alpha,beta-alkenoic esters. In contrast to the behavior with the corresponding Z esters, deprotonation of the E esters with LDA does not require an activator. Treatment of the dienolate intermediates formed with chlorotrimethylsilane yields (O-methyl-C,O-bis(trimethylsilyl)ketene acetals, and alkylation furnishes (E)-alpha-alkyl beta,gamma-unsaturated esters. Protodesilylation of the latter compounds with tetra-n-butylammonium fluoride followed by hydrolytic workup provides trisubstituted 2-alkenoates.
Direct C–C Bond Formation of Allylic Alcohols with CO<sub>2</sub> toward Carboxylic Acids by Photoredox/Nickel Dual Catalysis
作者:Zhengning Fan、Shenhao Chen、Song Zou、Chanjuan Xi
DOI:10.1021/acscatal.2c00418
日期:2022.3.4
Carboxylation of allylic alcohols with carbondioxide is accomplished by photoredox/nickel dual catalysis, generating linear acids exclusively with good Z/E stereoselectivity. Hantzsch ester is employed as the reductant instead of stoichiometric metallic reductants, and the reaction can be conducted under room temperature with a blue LED light source. Mechanisticstudies reveal that the presence of
烯丙醇与二氧化碳的羧基化是通过光氧化还原/镍双重催化完成的,仅生成具有良好Z/E立体选择性的线性酸。采用 Hantzsch 酯代替化学计量的金属还原剂作为还原剂,反应可以在室温下用蓝色 LED 光源进行。机理研究表明,该催化体系中水的存在对反应的成功至关重要,并且反应更有可能在原位形成的烯丙基碳酸氢盐的氧化加成中进行。
Analogs of Alpha Galactosyceramide and Uses thereof
申请人:Cerundolo Vincenzo
公开号:US20090239813A1
公开(公告)日:2009-09-24
There are disclosed compound of formula I, in which R
1
represents a hydrophobic moiety adapted to occupy the C′ channel of human CDId, R
2
represents a hydrophobic moiety adapted to occupy the A′ channel of human CDId, such that R
1
fills at least at least 30% of the occupied volume of the C′ channel compared to the volume occupied by the terminal nC
14
H
29
of the sphingosine chain of α-galactosylceramide when bound to human CDId and R
2
fills at least 30% of the occupied volume of the A′ channel compared to the volume occupied by the terminal nC
25
H
51
of the acyl chain of α-galactosylceramide when bound to human CDId R
3
represents hydrogen or OH, R
a
and R
b
each represent hydrogen and in addition, when R
3
represents hydrogen, R
a
and R
b
together may form a single bond, X represents or —CHA(CHOH)
n
Y or —P(═0)(0
−
)0CH
2
(CH0H)
m
Y, in which Y represents CHB
1
B
2
, n represents an integer from 1 to 4, m represents 0 or 1, A årepresents hydrogen, one of B
1
and B
2
represents H, OH or phenyl, and the other represents hydrogen or one of B
1
and B
2
represents hydroxyl and the other represents phenyl, in addition, when n represents 4, then A together with one of B
1
and B
2
together forms a single bond and the other of B
1
and B
2
represents H, OH or OSO
3
H and pharmaceutically acceptable salts thereof; the compounds of formula I are indicted for use in the treatment of a virus, microbial infection, parasite, an autoimmune disease, cancer, allergy or asthma