Copper catalyzed aminolysis of bromoallenes as a new efficient route to propargylamines

Development of Useful Reactions Based on the Novel Reactivities of Allenic Compounds and Their Application to Tandem Cyclizations

This review highlights a recent study on allenic compounds by the author's group. In the first section, the organocopper-mediated ring-opening reaction of ethynylaziridines and palladium-catalyzed reductive synthesis of allenes are described. In the second section, palladium-catalyzed stereoselective cyclization of allenes, including the tandem reaction, leading to aziridines, pyrrolidines, benzoisoindoles, and cyclopropanes is presented. The final section reviews aziridination and medium-ring formation due to the intramolecular reaction of bromoallenes. The latter reaction is based on the author's recent discovery that bromoallenes can act as allylic dication equivalents in the presence of a palladium catalyst and alcohol.

Development of Useful Reactions Involving Tandem Cyclizations Based on the Novel Reactivities of Allenic Compounds

This review highlights author's recent study on allenic compounds. In the first section, organocopper-mediated ring-opening reaction of ethynylaziridines and palladium-catalyzed reductive synthesis of allenes including those which are not accessible by other means, are described. In the second section, palladium-catalyzed stereoselective cyclization of allenes and tandem reaction leading to aziridines, pyrrolidines, benzoisoindoles, and cyclopropanes are presented. The final section presents aziridination and medium-ring formation by intramolecular reaction of bromoallenes, which are scarcely investigated until quite recently. The latter reaction is based on our recent discovery that bromoallenes can act as allylic dication equivalents in the presence of a palladium catalyst and alcohol.

Preparation and Cyclization of Some N-(2,2-Dimethylpropargyl) Homo- and Heteroaromatic Amines and the Synthesis of Some Pyrido[2,3-d]pyrimidines

The Cu(i) catalyzed cyclization of o-substituted N-(2,2-dimethylpropargyl)anilines yields 8-substituted 2,2-dimethyl-1,2-dihydroquinolines, while m-substituted analogues provide a mixture of 5- and 7-substituted dihydroquinoline systems. This reaction can be extended to 2-amino-N-(2,2-dimethylpropargyl)anthracene, yielding a dihydronaphtho[2,3-f]quinoline product, and to aminoquinoline derivatives, which yield substituted phenanthroline products. Pyridine analogues did not cyclize, apparently because of complexation with the copper reagent. An alternative synthetic approach to these cyclized products, when complexation may be a problem, is illustrated by the following example. 2-Chloro-4-N-(2,2-dimethylpropargyl)pyrimidine was reduced using a Lindlar catalyst to the corresponding alkene which did not undergo an amino-Claisen rearrangement. However, the 5-bromopyrimidine alkene analogue underwent addition with phenylselanyl bromide to give a product that cyclized, using butyllithium, to a pyrido[2,3-d]pyrimidine selenium-containing product from which the selenium moiety could be removed to yield either a dihydro- or a tetrahydro-pyrido[2,3-d]pyrimidine system. A Heck reaction on the 5-bromopyrimidine alkene gave a 5-methylene-6,7-dihydro-5H-pyrrolo[2,3-d]pyrimidine.

Cu(I)-catalyzed direct addition and asymmetric addition of terminal alkynes to imines

A Cu(I)-catalyzed direct addition of alkynes to imines was developed. The process is simple and provides a diverse range of propargylamines in high enantiomeric excess and good yield both in water and in toluene. The absolute configuration of such addition products has been determined by x-ray crystallography.

A highly cis-selective synthesis of 2-ethynylaziridines by intramolecular amination of chiral bromoallenes: improvement of stereoselectivity based on the computational investigation

The base-mediated intramolecular amination of bromoallenes having an axial chirality is described. The treatment of (4S,aR)-4-alkyl-4-[N-(arylsulfonyl)amino]-1-bromobuta-1,2-dienes with NaH in DMF affords 2,3-cis-2-ethynylaziridines in good to excellent selectivity (2,3-cis:trans = 92:8-99:1). The reaction of (4S,aS)-bromoallenes with NaH/DMF also gives 2,3-cis-2-ethynylaziridines selectively (79:21-91:9). These experimental results have been rationalized by B3LYP density functional calculations together with the 6-31+G(d) basis set and the Onsager solvation model. The transition structures for cis-aziridine formation of both (4S,aR)- and (4S,aS)-bromoallenes in DMF are favored over the corresponding trans transition structures by 4.35 and 1.41 kcal/mol, respectively. Furthermore, the calculations predicted that a less polar solvent gives higher cis selectivity for (4S,aS)-bromoallenes. In fact, improvement of the cis selectivity to 99:1 has been realized by using a less polar solvent such as THF. The cyclization of bromoallenes bearing a beta- or gamma-amino group also affords four- and five-membered azacycles in a highly cis-selective manner.

Stereoselective synthesis of chiral 2,3-cis-2-ethynylaziridines by base-mediated intramolecular amination of bromoallenes

[reaction: see text] Novel stereoselective synthesis of 2,3-cis-2-ethynylaziridines from amino allenes is presented. While sodium hydride mediated intramolecular amination of (4S,aS)-4-alkyl-4-[N-(arylsulfonyl)amino]-1-bromobuta-1,2-dienes yields a mixture of 2,3-cis- and 2,3-trans-2-ethynylaziridines in which the cis-isomer predominates (79:21-89:11), the amination of (4S,aR)-isomers affords 2,3-cis-aziridines in excellent selectivities (91:9-100:0). Conversion of 2,3-trans-2-ethynylaziridines into the corresponding cis-isomers via a sequence of reactions (methanesulfonic acid mediated ring-opening reaction, bromination, and aziridination) is also described.