糖鎖の生物学的重要性が明らかになるにつれて,有機合成による糖鎖合成への期待が高まりつつある。二糖類・多糖類の合成は,有機合成化学では,糖ユニットを結合させるグリコシル化反応を鍵反応として行われる。グリコシル化反応を中心に,糖鎖合成について述べる。

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高等学校の化学学習の中で,「有機立体化学」は理解するのが難しい分野である。その理由は,分子を三次元的に考えて理解することと,似かよったカタカナの専門用語に慣れること,が必須だからである。ここでは,似かよったカタカナの専門用語を系統的に解説する。また,三次元空間の把握には分子模型を使用することが効果的であることにもふれる。

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In order to rationalize and correlate a variety of chemistry exhibited by heteroatoms, “heteroatom effect”, a new term, is proposed and its meaning is defined with the emphasis on the role of an unshared electron pair. For the first row heteroatoms (N, O), heteroatom effect is confined to the effect of unshared electron pair and the latter is classified into the ability to stabilize carbocations due to stereoelectronic effect of Deslongchamps sense and the ability to coordinate with metal cations, especially with lithium ion, to effect ortho-lithiation and to generate pseudo-five membered ring intermediates for controlling stereoselectivity.
For the 2nd, 3rd, and 4th row heteroatoms of IVB, VB, VIB and VIIB groups, heteroatom effect is classified into three effects on the basis of i) role of unshared electron pair, ii) role of valence expansion of the central atom, and iii) role of low lying orbital of σ^*_c-x. Importance of electron-rich and polarizable three-center four-electron bond is implicated to explain the geometry and reactivity of σ- and π- hypervalent molecules.

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The Diels-Alder reaction is one of the most valuable reactions in synthetic organic chemistry. This [4+2] cycloaddition produces a cyclohexene derivative with concomitant generation of up to four new stereogenic centers. Particularly, intramolecular version has attracted many organic chemists due to forming polycyclic skeleton with high regio- and stereoselectivity under mild conditions. Thus, the intramolecular Diels-Alder reaction has shown its broad utility for the construc-tion of various complex ring systems. In this review, we summarize the regio-, endo/exo, and/or π-facial selective intramolecular Diels-Alder reactions of type I for total synthesis of natural prod-ucts, which have been published in recent years.

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環状アゾ化合物である2,3-diazabicyclo[2,2,1]hept-2-ene(DBH)は、光反応によって脱窒素を伴うビラジカルが生成する事が知られている。我々はメタノ橋頭位をジオキソラン(-O(CH₃)₃O-)で置換したDBH誘導体AZの三重項増感光反応において、例外的なβ―炭素炭素結合開裂反応が起こる事を見出した。本発表ではこの反応におけるメタノ橋頭位の置換基効果を実験及び計算化学の両面から検討する

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Despite considerable progress and extensive effort, a general method for highly stereoselective glycosylation particularly for the 1, 2-cis-glycosylation has not yet been developed and therefore is required. The α/β-stereoselectivity in glycosylation can be affected by the steric and stereoelectronic (anomeric) effects around the anomeric center, which depend on the conformation of the glycosyl donor substrates. Therefore, we hypothesized that highly α- and β-selective glycosylation can be realized by employing conformationally restricted substrates. We showed that the α/β-stereoselectivity was significantly increased by the conformational restriction and was completely inverted by changing the substrate conformation from the ⁴C₁-form into the ¹C₄-form in radical and nucleophilic C-glycosylation reactions as well as in O-glycosylation reactions. The conformational restriction of substrates also effectively facilitates the α- and β-selective radical cyclization reaction at the anomeric position. Using the method, C-glucoside trisphosphates designed as Ca²⁺-mobilizing agents were successfully synthesized.

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