高度にダイアステロ選択性のある水素化により,β-ヒドロキシ保護形態のβ-デルタ-ラクトンが生成される. デルタ・ラクトン形状の改変した見方
Svante Brandänge1, Magnus Färnbäck, Hans Leijonmarck
1Department of Organic Chemistry, Arrhenius Laboratory, Stockholm University, SE-106 91, Stockholm, Sweden. svante@organ.su.se
Journal of the American Chemical Society
|September 25, 2003
まとめ
パラジウム触媒による不飽和デルタ・ラクトンの水素化により,高ダイアステロ選択性を持つ飽和ラクトンが得られます. 形状分析は,以前に受け入れられたモデルを超えた多様なリング構造を明らかにします.
科学分野:
- 有機化学 オーガニック・ケミストリー
- ステレオ化学 ステレオ化学
- コンピューティング・ケミストリー
背景:
- パラジウム触媒による水素化は,有機合成における重要な反応である.
- 水素化のステレオ化学的結果を理解することは,分子構造の制御に極めて重要です.
- デルタラクトンは,天然製品や医薬品における重要な構造モチーフです.
研究 の 目的:
- 置換されたアルファ,ベータ不飽和デルタラクトンのパラジウム触媒化水素化におけるステレオ化学的制御を調査する.
- トランス-5,6-非置換の1-オクサ-3-サイクロヘクセン-2-オンを水素化するためのステレオ化学的汎用化を開発する.
- 実験的および計算的方法を用いて,飽和デルタ・ラクトンの形状的景観を探求する.
主な方法:
- Palladium on Carbon (Pd/C) を使用したエノールMEMエーテルとエノールアセテットの水素化.
- 67の飽和デルタ・ラクトン化合物のX線結晶学的データの分析.
- アブ・イニシオ計算 (HF/6-31G) で,構成エネルギーと移行状態を決定する.
主要な成果:
- エノールMEMエーテルとエノールアセテートの水素化は,非常に高いダイアステロ選択性 (>99%) で,飽和デルタ・ラクトンに進行した.
- ステレオ化学のルールは,横のトランスからC(6) 置換体へのトランス-5,6-非置換の1-オクサ-3-サイクロヘクセン-2-オンヒドロゲネートとして策定された.
- 形状分析により,飽和デルタラクトンの有意な多様性が明らかになり,狭いエネルギー範囲内で複数のアクセス可能なコンフォマー (半椅子,ボート,椅子,封筒,スイック) が存在しました.
結論:
- パラジウム触媒による水素化は,飽和デルタ・ラクトンを合成するための優れたステレオ化学制御を提供します.
- 飽和デルタ・ラクトンの形状的行動は,これまで考えられていたよりも複雑で,より広い範囲のアクセシブルな形状を含む.
- この発見は,ステレオ選択性のメカニズム的理解を提供し,デルタ・ラクトンの構成パラダイムを拡張します.
関連する概念動画
02:06Newman Projections
Different notations are used to represent the three-dimensional structure of molecules on two-dimensional surfaces. One of the most commonly used representations is the dash-wedge formula. The dashed wedges, solid wedges, and the plane lines indicate the groups situated behind the plane, coming out of the plane, and in the plane, respectively.
The organic molecules rotate across the single bonds leading to numerous temporary three-dimensional structures of varying energy known as conformers.
The organic molecules rotate across the single bonds leading to numerous temporary three-dimensional structures of varying energy known as conformers.
02:04Oxidation of Alkenes: Anti Dihydroxylation with Peroxy Acids
Diols are compounds with two hydroxyl groups. In addition to syn dihydroxylation, diols can also be synthesized through the process of anti dihydroxylation. The process involves treating an alkene with a peroxycarboxylic acid to form an epoxide. Epoxides are highly strained three-membered rings with oxygen and two carbons occupying the corners of an equilateral triangle. This step is followed by ring-opening of the epoxide in the presence of an aqueous acid to give a trans diol.
01:57Preparation of Diols and Pinacol Rearrangement
Compounds bearing two hydroxyl groups are known as diols. When the hydroxyl groups are located on adjacent carbon atoms, the diols are called vicinal diols or glycols. Under acidic conditions, vicinal diols undergo a specific reaction called pinacol rearrangement.
The reaction begins with transferring a proton from the acid catalyst to one of the hydroxyl groups, producing an oxonium ion.
The reaction begins with transferring a proton from the acid catalyst to one of the hydroxyl groups, producing an oxonium ion.
01:28Structures of Carboxylic Acid Derivatives
Structure of Carboxylic Acid Derivatives
Carboxylic acid derivatives contain an acyl group attached to a heteroatom such as chlorine, oxygen, or nitrogen. The carbonyl carbon and oxygen are both sp2-hybridized with an unhybridized p orbital.
The three sp2 orbitals of the carbonyl carbon form three σ bonds, one each with the carbonyl oxygen, the α carbon, and the heteroatom, whereas the other two sp2 orbitals of the carbonyl oxygen are occupied by the lone pairs. Further, the unhybridized p...
Carboxylic acid derivatives contain an acyl group attached to a heteroatom such as chlorine, oxygen, or nitrogen. The carbonyl carbon and oxygen are both sp2-hybridized with an unhybridized p orbital.
The three sp2 orbitals of the carbonyl carbon form three σ bonds, one each with the carbonyl oxygen, the α carbon, and the heteroatom, whereas the other two sp2 orbitals of the carbonyl oxygen are occupied by the lone pairs. Further, the unhybridized p...
01:18β-Dicarbonyl Compounds via Crossed Claisen Condensations
Crossed Claisen condensations are base-promoted reactions between two different ester molecules producing β-dicarbonyl compounds. The reaction involving esters, with both containing α hydrogen, results in a mixture of four different products that are difficult to isolate. This reduces the synthetic utility of the reaction.
01:28Stability of Conjugated Dienes
Introduction
A comparison of the enthalpies of hydrogenation of dienes reveals that conjugated dienes release less heat on hydrogenation, rendering them more stable than their nonconjugated analogs.
A comparison of the enthalpies of hydrogenation of dienes reveals that conjugated dienes release less heat on hydrogenation, rendering them more stable than their nonconjugated analogs.