Bicyclic dihydrothiophenes are readily prepared by a radical cascade cyclization reaction triggered by the addition of a thiyl radical under thermal or photoirradiation conditions. The translocated radical attacks the sulfur atom in the initial radical donor unit in an SHi manner. Sufficient stereoselectivity is achieved when a large excess of disulfide is used for the reaction under photoirradiation conditions. The reaction in the absence of solvents provides vinylsulfides instead of dihydrothiophenes. Thus, the sulfur atom in the thiyl radical serves as a sulfur biradical synthetic equivalent.
Optically active seven-membered lactones, dimethyleneoxazepanones, were readily prepared in good yields from chiral β-(N-propargylic)amino-α-methylene carboxylic acid tert-butyl esters in the presence of catalytic amounts of Ph3PAuCl and Cu(OTf)2. A smooth 7-exo-dig cyclization was observed.
SummaryBicyclodihydrosiloles were readily prepared from optically active enyne compounds by a radical cascade reaction triggered by tris(trimethylsilyl)silane ((Me3Si)3SiH). The reaction was initiated by the addition of a silyl radical to an α,β-unsaturated ester, forming an α-carbonyl radical that underwent radical cyclization to a terminal alkyne unit. The resulting vinyl radical attacked the silicon atom in an SHi manner to give dihydrosilole. The reaction preferentially formed trans isomers of bicyclosiloles with an approximately 7:3 to 9:1 selectivity.
Gold(I)-Catalyzed Synthesis of Optically Active 1,4-Oxazepan-7-ones. -A novel one-step synthesis of enantioenriched 1,4-oxazepan-7-ones is achieved by cyclization of optically active alkynyl esters in the presence of Ph 3PAuCl and Cu(OTf)2 as the catalysts. The resulting oxazepanones contain two exocyclic methylene groups, which are prone to further functionalization. -(KAMIMURA*, A.; YAMANE, Y.; YO, R.; TANAKA, T.; UNO, H.; J. Org. Chem. 79 (2014) 16, 7696-7702, http://dx.doi.org/10.1021/jo501254x ; Dep. Appl. Mol. Biosci., Grad. Sch. Med., Yamaguchi Univ., Ube, Yamaguchi 755, Japan; Eng.) -Mais 08-254
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