Photosensitized [4+2]- and [2+2]-Cycloaddition Reactions of N-Sulfonylimines

The synthesis of polycyclic compounds is of high interest due to the prevalence of these motifs in drugs and natural products. Herein, we report on the stereoselective construction of 3D bicyclic scaffolds and azetidine derivatives by modulation of N-sulfonylimines to achieve either [4+2]- or [2+2]-cycloaddition reactions. The utility of the method was established by further modulation of the product. Mechanistic studies are also included, which support reaction via Dexter energy transfer.     

Synthesis of New 4,4a-Dihydroxanthones via [4+2]-Cycloaddition Reaction

Russian Journal of General Chemistry - The effect of electronic properties of substituents in the reactants on the [4+2]-cycloaddition of 3-vinyl-chromen-4-ones (dienes) and N-vinylpyrrolidines...     

Stereoselective [4+2]-Cycloaddition with Chiral Alkenylboranes

A method for the stereoselective [4+2]-cycloaddition of alkenylboranes and dienes is presented. This transformation was accomplished through the introduction of a new strategy that involves the use of chiral N-protonated alkenyl oxazaborolidines as dieneophiles. The reaction leads to the formation of products that can be readily derivatized to more complex structural motifs through stereospecific transformations of the C−B bond such as oxidation and homologation. Detailed computation evaluation of the reaction has uncovered a surprising role of the counterion on stereoselectivity.     

[2+4]-Cycloaddition reactions of methyl trifluoropyruvate trifluoroacetylimine

Methyl trifluoropyruvate trifluoroacetylimine (I) reacts regioselectively with olefins to form dihydrooxazines (II)-(VII). In its reactions with 1,3-dienes, too, compound (I) exhibits properties of a 1,3-heterodiene rather than a dienophile. Acid hydrolysis of the synthesized oxazines results in their conversion to substituted -amino--trifluoromethyltetrahydrofuran-2-ones (XII)-(XVI).Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 5, pp. 1130–1133, May, 1991.     

Synthetic Transformations of Higher Terpenoids: VIII. [4+2]-Cycloaddition Reactions of Lambertianic Acid

The Diels-Alder reaction of lambertianic acid with maleic anhydride occurred in a stereoselective fashion and yielded diastereoisomeric (1R,2S,6R,7R)- and (1S,2R,6S,7S)-exo-adducts. The latter reacted with L-valinol to give the corresponding diterpenoid imides, 4-aza-9-oxabicyclo[2.2.1]dec-8-enes. Reactions of lambertianic acid with N-substituted maleimides in the presence of Lewis acids afforded diastereoisomeric adducts having both exo and endo configuration. Some transformations of the adducts were examined with a view to obtain cantharidin and dihydroisoindole analogs.     

[2+4]-Cycloaddition of fluoroolefins and fluoroazomethines with furan

Conclusions Terminal and internal fluoroolefins and polyfluoro-1-alkenylsulfonyl fluorides as well as perfluoro-3-aza-2-pentene react with furan to give [2+4]-cycloadducts. Perfluoroazapropene and 1-cyanotetrafluoro-2-azopropene do not undergo this cycloaddition reaction.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 4, pp.897–900, April, 1988.     

Synthesis of 1,4-Cyclohexadiene Carboxylates through a Formal [2+4]-Cycloaddition of Propiolates under Cobalt Catalysis

A low-valent cobalt(I) complex, formed from the reduction of CoBr₂(dppe) with zinc, acts as catalyst for the efficient [2+4] cycloaddition of β-alkyl, cycloalkyl and aryl substituted propiolates to dienes. This transformation yields synthetically relevant 1,4-cyclohexadiene carboxylates in good to excellent yields. Furthermore, the target compounds are novel lead structures for the discovery of fragrance ingredients from the fruity, floral and spicy odor family.     

有机催化不对称[4+2]环加成反应*

有机催化不对称合成反应是目前国内外研究最为活跃的领域之一。不对称[4+2]环加成（Diels-Alder）反应是合成光学活性环状化合物的有效手段,目前报道的催化不对称Diels-Alder反应的有机催化剂主要有手性咪唑啉酮、手性Br?nsted酸、手性伯胺、金鸡纳碱衍生物等。本文对各类有机催化剂在有机催化不对称Diels-Alder反应中的应用研究进展,以及不对称诱导反应的机理进行了评述。     

海洋环境中的天然溴代有机物

近些年来,环境中的溴代有机污染物逐渐成为人们关注的热点。最近的研究发现,海洋环境中的一些溴代有机物并非来自于人为污染,而是来自于天然合成。海洋环境中存在的这些天然溴代有机物引起了人们极大的兴趣。这些天然溴代有机物在海洋生物、底泥、海水以及大气中广泛存在,并可在海洋哺乳动物体内富集。毒理学研究表明,一些天然溴代有机物具有一定的生物活性与毒性。因此,深入研究天然溴代有机物的环境分布与环境影响具有重要的意义。本文介绍了代表性天然溴代有机物的环境分布、毒性及其可能的来源,并对其未来研究方向和趋势作了展望。