Relative Stabilities of Some Synthetically Useful 2,3-<i>cis</i>-Disubstituted Aziridines and Their 2,3-Trans Isomers

The relative stabilities of synthetically useful 2,3-cis/trans pairs of 2,3-disubstituted aziridines were investigated theoretically by performing molecular orbital calculations at the MP2/6-31G**/RHF/6-31G** level of theory. The results showed clearly that a functional group on the nitrogen atom of the aziridine ring plays a very important role in conjunction with the relative stabilities of these pairs of isomers. There is a tendency that the 2,3-cis isomer bearing tetrahedral structure on the aziridine nitrogen is preferable. Bulky substituents such as a phenyl group on aziridine atoms can also affect the relative stability sterically

Aluminum-Controlled Reactivity and Diastereoselectivity toward Radical Reactions of Optically Active Aldimines with Metallic Samarium

The intermolecular pinacol-type coupling reaction and allylation reaction of optically active imines bearing a β-hydroxy group were performed stereoselectively with metallic samarium after treatment of the imines with trimethylaluminum

A New Synthesis of the Central Substructure of Botryococcenes

A New Synthesis of the Central Substructure of Botryococcene

Reactions of <i>N</i>-Arylsulfonyl-2,3-<i>cis</i>- and <i>N</i>-Arylsulfonyl-2,3-<i>trans</i>-3-alkyl-2-vinylaziridines with Organocopper Reagents: Importance of 2,3-<i>cis</i>-Stereochemistry in Controlling Regio- and Stereoselectivity

Although reactions of 2,3-trans-N-arylsulfonyl-3-alkyl-2-alkenylaziridines with organocopper reagents give a mixture of two or three products, the corresponding 2,3-cis-isomers provide a highly efficient route to synthetically important nonracemic (E)-allylamines. It is also found that the reaction proceeds via the well-known anti-SN2‘ pathway

Asymmetric Total Synthesis of Halicholactone

The asymmetric total synthesis of the marine metabolite, halicholactone 1, is described. The bis-allylic triol 6 with three chiral centers at C8, C12, and C15 was constructed by [2,3]-sigmatropic rearrangement of the sulfoxide 18, which was prepared stereoselectively using the chirality of (diene)Fe(CO)3 complexes. Introduction of the trans-substituted cyclopropane subunit into 21 was successfully achieved using the modified regio- and stereoselective Simmons−Smith reaction. The use of RCM (ring-closing metathesis) methodology (4 → 35) was pivotal for the formation of a nine-membered unsaturated lactone fragment of halicholactone 1. As this approach is flexible and stereoselective, other oxylipins could be synthesized by the protocol described herein

Utility of a Diene−Tricarbonyliron Complex as a Mobile Chiral Auxiliary: Regio- and Stereocontrolled Functionalization of Acyclic Diene Ligands

Stereoselective construction of contiguous stereogenic centers of acyclic compounds by using the Fe(CO)3 moiety as a mobile chiral auxiliary is described. Although the reactions of acyclic (pentadienyl)iron(1+) cations with nucleophiles generally occur in a stereoselective but nonregioselective manner, giving rise to several regioisomers, O-acyl and O-phosphoryl cyanohydrin Fe(CO)3 complexes 2−5 undergo regio- and stereoselective 1,5-nucleophilic substitution with several heteroatomic nucleophiles, giving the 6-substituted hepta-2,4-dienonitrile Fe(CO)3 complexes 6 and 7, that is, 1,2-migration products of the Fe(CO)3 group. These products were obtained as single products, even if the starting materials 3−5 were a mixture of diastereomers. The (2E,4E)/(2E,4Z) selectivity of the 1,5-substituted products (6/7) is strongly dependent on the Lewis acid catalyst, triphenylcarbenium perchlorate (TrClO4) giving 6 (method A) and BF3·etherate giving 7 (method B), respectively. Furthermore, by applying iterative 1,5-nucleophilic substitution to 6, both 6,7-anti-disubstituted (2E,4E)-adduct anti-10 and 6,7-syn-disubstituted (2E,4Z)-one syn-11 were synthesized stereoselectively by switching the reaction conditions (method A and method B). The third introduction of the ethylsulfanyl group into anti-10 proceeded efficiently by the same treatment of 10 with ethanethiol and TrClO4 to afford the 6,7-anti-7,8-anti-trisubstituted (2E,4E)-adduct 19. Further manipulation successfully converted 19 to the N-Boc-O-Me derivative 24 of anti-2,3-amino alcohol 25, which had been isolated from a marine sponge

Synthesis of Allenes from Allylic Alcohol Derivatives Bearing a Bromine Atom Using a Palladium(0)/Diethylzinc System

A general and efficient synthesis of allenes using a palladium(0)/diethylzinc system is described. Treatment of mesylates or trichloroacetates of (E)- or (Z)-2-bromoalk-2-en-1-ols with diethylzinc in the presence of a catalytic amount of palladium(0) affords allenes bearing an aminoalkyl, alkyl, or aryl substituent(s) in good to high yields. No transfer of chirality from the stereogenic center carrying the mesyloxy group to the allene was observed

Stereoselective Synthesis of 2-Alkenylaziridines and 2-Alkenylazetidines by Palladium-Catalyzed Intramolecular Amination of α- and β-Amino Allenes

Whereas palladium-catalyzed reaction of N-arylsulfonyl-α-amino allenes with an aryl iodide (4 equiv) in the presence of potassium carbonate (4 equiv) in DMF at around 70 °C affords the corresponding 3-pyrroline derivatives, the reaction in refluxing 1,4-dioxane under otherwise identical conditions yields exclusively or most predominantly the corresponding 2-alkenylaziridines bearing an aryl group on the double bond. Similarly, N-arylsulfonyl-β-amino allenes can be also cyclized into the corresponding alkenylazetidines bearing a 2,4-cis-configuration under palladium-catalyzed cyclization conditions in DMF

Stereoselective Synthesis of 2-Alkenylaziridines and 2-Alkenylazetidines by Palladium-Catalyzed Intramolecular Amination of α- and β-Amino Allenes

Whereas palladium-catalyzed reaction of N-arylsulfonyl-α-amino allenes with an aryl iodide (4 equiv) in the presence of potassium carbonate (4 equiv) in DMF at around 70 °C affords the corresponding 3-pyrroline derivatives, the reaction in refluxing 1,4-dioxane under otherwise identical conditions yields exclusively or most predominantly the corresponding 2-alkenylaziridines bearing an aryl group on the double bond. Similarly, N-arylsulfonyl-β-amino allenes can be also cyclized into the corresponding alkenylazetidines bearing a 2,4-cis-configuration under palladium-catalyzed cyclization conditions in DMF

First Palladium-Catalyzed Aziridination Reaction of Amino Allenes

First Palladium-Catalyzed Aziridination Reaction of Amino Allene