25144-05-2Relevant academic research and scientific papers
Al-isopropoxydiisobutylalane: A study of the effect of solvent on the rate and stereoselectivity of cyclic ketone reduction
Bahia, Perdip S.,Jones, Matthew A.,Snaith, John S.
, p. 9289 - 9291 (2007/10/03)
The effect of solvent on the rate and stereoselectivity of cyclic ketone reduction by Al-isopropoxydiisobutylalane (DIBAiOPr) has been investigated. In dichloromethane, DIBAiOPr behaves as a bulky reducing agent, approaching the carbonyl group along an equatorial trajectory to produce the axial alcohol with > 10:1 stereoselectivity. In sharp contrast, reduction in toluene gives the complementary outcome, affording the thermodynamically more stable isomer with > 99:1 stereoselectivity.
Reduction of aliphatic and aromatic cyclic ketones to sec-alcohols by aqueous titanium trichloride/ammonia system. Steric course and mechanistic implications
Clerici, Angelo,Pastori, Nadia,Porta, Ombretta
, p. 2235 - 2243 (2007/10/03)
In contrast to the dissolved metal and metal hydride reductions, the reduction of cyclic ketones by the aqueous TiCl3/NH3 system favours the formation of the less thermodynamically stable axial alcohol. The ammonium ion formed in situ is essential for the reduction to proceed because it behaves as a mild Br?nsted acid in basic medium and favours the protonation of the intermediate ketyl. The corresponding α-hydroxy radical is then rapidly reduced under conditions where the first electron transfer to the substrate takes place. We suggest that the stereoselectivity is determined by the second reduction step, which occurs through the less hindered transition state, regardless of whether the radical to be reduced is thermodynamically favoured or not.
Generation and reactivity of oxazolidinone derived N-acyl radicals
Keck, Gary E.,Grier, Mark C.
, p. 1657 - 1659 (2007/10/03)
The N-acyl(phenylseleno)oxazolidinone 5 was prepared (85% yield) by treatment of the lithium salt of oxazolidinone with triphosgene, followed by addition of benzeneselenol. Reduction of 5 with n-Bu3SnH/AIBN gave the N- formyloxazolidinone 6 (99%) and reaction with allyltri-n-butylstannane gave 7 (89%). Bimolecular additions to various alkenes using the N-acyl radical derived from oxazolidinone 5 were also studied. Best results were obtained with electron rich olefins, such as enol ether derivatives. Eight such additions are reported, with yields ranging from 51-90%. Two prochiral substrates showed significant levels of diastereoselectivity in reactions with 5/Bu3SnH.
Preparation and use of sterically hindered organobis(2,4,6-triisopropylphenyl)hydroborates and their polystyrene derivatives for the diastereoselective reduction of ketones
Smith, Keith,El-Hiti, Gamal A.,Hou, Duanjie,DeBoos, Gareth A.
, p. 2807 - 2812 (2007/10/03)
Preparations of benzyl and phenylbis(2,4,6-triisopropylphenyl)hydroborates [organoditripylhydroborates] are outlined. The lithium and potassium benzylditripylhydroborates reduce substituted cyclohexanones with diastereoselectivities comparable to those obtained with the most selective reagents known (eg. 99% cis-4-methylcyclohexanol from 4-methylcyclohexanone). Lithium phenylditripylhydroborate also reduces ketones with significant selectivity. For example, 4-methylcyclohexanone is reduced to cis-4-methylcyclohexanol in 88% isomeric purity. Unlike with most other highly selective reagents the reactions take place at room temperature and have the additional advantage that the boron reagent can be recovered quantitatively. Coupling of Merrifield's resin with ditripylfluoroborane in the presence of lithium naphthalenide affords (ditripylborylmethyl)polystyrene. Similarly, coupling of bromopolystyrene with ditripylfluoroborane in the presence of n-BuLi affords (ditripylboryl)polystyrene. Reactions of these polymeric organoboranes with t-BuLi give the corresponding polymer-supported lithium hydroborates. Lithium ditripylhydroboratylmethylpolystyrene reduces cyclic ketones in identical fashion to its non-polymeric counterpart, giving the corresponding thermodynamically less stable alcohols in 99% or better isomeric purity. Similarly, lithium ditripylhydroboratylpolystyrene behaves like its non-polymeric counterpart and reduces 4-methylcyclohexanone to cis-4-methylcyclohexanol in 89% isomeric purity. Recovery and reuse of the organoboranes are even easier for the polymeric reagents. The Royal Society of Chemistry 1999.
Stereo- and chemoselective transfer hydrogenation of carbonyl groups with RuCl2(PPh3)3 and BINAP-Ru as catalysts and et3NH+H2PO2-·1,5H 2O as a hydrogen donor
Khai, Bui The,Arcelli, Antonio
, p. 6599 - 6602 (2007/10/03)
Using Et3NH+H2PO2-.1.5 H2O as a hydrogen donor, the RuCl2(Ph3P)3, RuCl2(PPh3)3 / C and BINAP-Ru proved highly active catalysts for transfer hydrogenation of ketones under milder conditions than other hydrogen donors. 2-Methyl-, 2-chloro-, 2-(ethoxycarbonyl)cyclohexanones and -cyclopentanones were reduced to the less stable axial alcohols in excellent diastereoisomeric excess (de: 90-100%), and the carbonyl group of α,β-unsaturated ketones was selectively reduced, in contrast with other hydrogen donors the C=C bond was reduced. Copyright
Silica Gel Supported Zinc Borohydride. A Novel Reagent for Hydration of Unactivated Alkenes and Alkynes
Ranu, Brindaban C.,Sarkar, Arunkanti,Saha, Manika,Chakraborty, Rupak
, p. 6579 - 6584 (2007/10/02)
A simple and general procedure for hydration of unactivated alkenes and alkynes producing less substituted alcohols selectively has been achieved by the reaction of the corresponding alkenes or alkynes on silica gel support with zinc borohydride in 1,2-dimethoxyethane.
Cyclization of (4-Methoxy-5-hexenyl)lithium
Bailey, William F.,Jiang, Xing-Long
, p. 6528 - 6533 (2007/10/02)
The cyclization of (4-methoxy-5-hexenyl)lithium (1), which was prepared by lithium-iodine exchange between 3-methoxy-6-iodo-1-hexene (2) and 1.75 molar equiv of t-BuLi in diethyl ether-n-pentane solution at -78 deg C, has been investigated in variety of solvent systems.The isomeric composition of the cis- and trans-1-methoxy-2-methylcyclopentane produced upon cyclization of 1 followed by quench with MeOH has been found to be dramatically dependent on the solvent system in which the isomerization is conducted.
