Directed reduction of .beta.-hydroxy ketones employing tetramethylammonium triacetoxyborohydride
作者:D. A. Evans、K. T. Chapman、E. M. Carreira
DOI:10.1021/ja00219a035
日期:1988.5
The mild reducing agent tetramethylammonium triacetoxyborohydride reduces acyclic P-hydroxy ketones to their corresponding anti diols with high diastereoselectivity. a-Alkyl substitution does not significantly affect the stereoselectivity of these reductions. In all cases examined, good to excellent yields of diastereomerically homogeneous diols were obtained. The mechanism of these reductions involves
温和的还原剂四甲基铵三乙酰氧基硼氢化物以高非对映选择性将无环 P-羟基酮还原为其相应的反二醇。α-烷基取代不会显着影响这些还原的立体选择性。在所有检查的情况下,都获得了良好到极好的非对映异构体均质二醇的产率。这些还原的机制涉及三乙酰氧基硼氢化物阴离子将乙酸盐与底物醇进行酸促进的配体交换。所得氢化物中间体,大概是烷氧基二乙酰氧基硼氢化物,还原近端 OH 0 OH OH 0 Me,NHB(OAc), Mew Me&OR - OR Me he
Lithium Hexamethyldisilazide-Mediated Enolizations: Influence of Triethylamine on <i>E</i>/<i>Z</i> Selectivities and Enolate Reactivities
作者:Peter F. Godenschwager、David B. Collum
DOI:10.1021/ja800250q
日期:2008.7.1
Lithium hexamethyldisilazide (LiHMDS) in triethylamine (Et 3N)/toluene is shown to enolize acyclic ketones and esters rapidly and with high E/ Z selectivity. Mechanistic studies reveal a dimer-based mechanism consistent with previous studies of LiHMDS/Et 3N. E/ Z equilibration occurs when <2.0 equiv of LiHMDS are used. Studies of the aldolcondensation and Ireland-Claisen rearrangement of the resulting
Diastereoselective Aldol Addition Using Boron Trichloride or Alkoxydichloroborane
作者:Hak-Fun Chow、Dieter Seebach
DOI:10.1002/hlca.19860690309
日期:1986.5.7
Under carefully controlled conditions, borontrichloride or alkoxydichloroborane/ethyldiisopropylamine in CH2Cl2 can be used to effect diastereoselective aldol additions of ethyl ketones to saturated, α, β-unsaturated, or aromatic aldehydes. The CC bond formation takes place with relative topicity ul (‘syn,’ configuration of the aldols), in selectivities ranging from 90 to 99% ds (Tables 1–3). Mechanistic
在精心控制的条件下,CH 2 Cl 2中的三氯化硼或烷氧基二氯硼烷/乙基二异丙胺可用于将乙基酮进行非对映选择性的醛醇缩合,形成饱和,α,β-不饱和或芳族醛。CC键的形成具有相对局部性ul(醛醇的“ syn ”构型),选择性范围为90%到99%ds(表1-3)。讨论了反应的机械方面。
Stereoseletive Reduction of<i>β</i>-Hydroxy Ketones to 1,3-Diols with the Aid of a Terphenylboronic Acid
作者:Hiroshi Yamashita、Koichi Narasaka
DOI:10.1246/cl.1996.539
日期:1996.7
stereoselective reduction of acyclic and cyclic β-hydroxy ketones. The terphenylboronic acid 1 and acyclic β-hydroxy ketones 2 are converted to the corresponding boronates by azeotropic removal of water. The resulting boronates are treated in situ with reducing reagents to give syn 1,3-diols 3 almost exclusively. Anti α-substituted β-hydroxy ketones 8 are also reduced to give anti, anti 1,3-diol 9 stereoselectively
The directed reduction of β-hydroxy ketones employing Me4NHB(OAc)3
作者:David A. Evans、Kevin T. Chapman
DOI:10.1016/s0040-4039(00)85367-8
日期:1986.1
The diastereoseiective reduction of a range of acyclic β-hydroxy ketones with triacetoxyborohydride is described. In all cases, the anti 1,3-diol diastereomer is the principal product (eq 1).