Regioselective opening of 2,3-epoxy alcohols with organocuprates. Enhanced C-2 selectivity through solvent effects.

In coordinating solvents (THF-DMEU or THF-TMEDA), increased selectivity for opening at C-2 of 2,3-epoxy alcohols is observed oith Me₂CuCNLi₂ prepared from low-halide MeLi.     

Regioselective reductions of 2,3-epoxy alcohols

Regioselective reduction of 3-substituted-2,3-epoxy alcohols to 1,3-diols with sodium bis(2-methoxyethoxy)aluminum hydride (Red-al) is shown to be a general reaction for these substitutes.     

Regioselective titanium mediated reductive opening of 2,3-epoxy alcohols

Lithium borohydride reduction of 2,3-epoxy alcohols was shown to yield 1,2-diols in high regioselectivity with the aid of titanium tetraisopropoxide in benzene solution.     

Regioselective reductions of 2,3-epoxy acetals with zinc-chlorotrimethylsilane and lithium aluminium hydride: convenient synthesis of 1,2 and 1,3-diones

A variety of 2,3-epoxy acetals have been found to undergo regioselective reductions with zinc-chlorotrimethylsilane and lithium aluminium hydride to give 2-hydroxy and 3-hydroxy acetals respectively. Their oxidation followed by hydrolysis furnished the corresponding 1,2- and 1,3-diones in good yields.     

Regioselective reductions of 23-epoxy acetals with lithium aluminum hydride: A reinvestigation.

Treatment of 2,3-epoxy acetals with lithium aluminum hydride gave the corresponding 2-hydroxy acetals, instead of the previously reported 3-hydroxy acetals.     

Ring opening of 2,3-epoxy phenyl ketones upon reaction with nitric oxide

Epoxide rings of 2,3-epoxy phenyl ketones were cleaved by nitric oxide, affording regioselectively the C-3 ring-opened products, erythro-α-hydroxyl nitrates (2), in a highly syn-selective manner (isolated yield of the erythro products up to 91%). Products were identified by NMR, MS, and X-ray crystallography. The reaction is assumed to be initiated by NO₂, unlike a nucleophilic attack.     

Regioselective reduction of 3-substituted 2,3-dihydrobenzothiadiazines with borohydrides

A simple and efficient synthetic path for N-1 or N-2 alkyl-substituted 2-aminobenzenesulfonamides was developed based on regioselective reduction with NaBH₃CN in different solvents.     

Regioselective cleavage of cis- and trans-2-methyl-3,4-epoxy alcohols with diethylpropynyl aluminum

The regioselectivity of the reaction of diethylpropynyl aluminum with diastereomeric 2-methyl-3,4-epoxy alcohols was studied. The preferred side of attack (1,3-diol vs 1,4-diol product) depends on the stereochemical disposition of the substituents. NMR studies showed that the regiochemistry of this reaction is governed by the aluminum coordination pattern. Protection of the alcohol with MEM provides the 1,3-diol product in systems where the free alcohol produced the 1,4-diols.     

Stereoselective synthesis of 2,3-epoxy alcohols mediated by a remote sulfinyl group

The influence of the sulfinyl group as a chiral auxiliary in the stereoselective addition of oxiranyllithiums to (S)-2-p-tolylsulfinylbenzaldehyde has been studied. All reactions evolve with retention of configuration at the starting lithiated carbon. Completely stereoselective additions have been observed when configurations at sulfur and the lithiated carbon are different (matched pair), whereas variable dr's values (ranging between 52:48 and >99:<1%) when they are identical (mismatched pair).     

Stereoselective alkynylation of trans-2,3-epoxy sulfides with double inversion of configuration by alkynylaluminums

A stereoselective alkynylation reaction of rans-1-phenylthio-2,3-epoxyalkanes with alkynylaluminums which proceeds via episulfonium ions, that is, with double inversion of configuration, has been developed.     

Regioselective reductive openings of acetals; mechanistic details and synthesis of fluorescently labeled compounds

Regioselective reductive openings of mixed phenolic-benzylic acetals, using BH3.NMe3-AlCl3, was investigated, and a mechanism where the outcome is directed by the electrostatic potential of the two oxygen atoms is presented. The regioselective acetal opening was used in the synthesis of a fluorescently labeled analogue to antiproliferative xylosides. The fluorescently labeled xyloside was tested for uptake, antiproliferative activity, and glycosaminoglycan priming in different cell lines. The xyloside was taken up by all cell lines but did not initiate glycosaminoglycan biosynthesis.     

Regioselective synthesis of pyrido[2,3-d]pyrimidines

The reaction of diethyl ethoxymethylenemalonate ( 1 ) and 6-amino-1,3-dimethyluracil ( 2 ) was determined to be regioselective. Under acidic conditions the product was the previously isolated 7-oxopyrido[2,3-d]pyrimidine ( 3 ), while in the presence of one equivalent of base followed by thermal cyclization, the isomeric 5-oxopyrido[2,3-d]pyrimidine ( 5 ) is formed.     

金属离子修饰的铂纳米金属簇催化2,3-戊二酮区域选择性氢化

近年来,α-二酮的不对称氢化引起了人们的极大兴趣[1～3].由于α-二酮分子内存在两个共轭的羰基,α-二酮的氢化包括两步反应,通过控制反应条件可以使反应停留在第一步氢化的阶段[3].在已往的文献报道中[1～3],氢化反应的底物均局限于对称的α-二酮,如2,3-丁二酮或3,4-己二酮.这类底物的第一步氢化并不涉及区域选择性的问题.以2,3-丁二酮为例,第一步氢化只生成3-羟基-2-丁酮一种产物.但是,象2,3-戊二酮之类的不对称α-二酮的氢化情况则复杂得多,因为在第一步反应中有2-羟基-3-戊酮和3-羟基-2-戊酮两种产物生成.因此,在研究不对称α-二酮的对映体选择性氢化时还必须顾及其区域选择性氢化.