ABSTRACT
Optically active seven-membered lactones, dimethyleneoxazepanones, were readily prepared in good yields from chiral ß-(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.
Subject(s)
Gold/chemistry , Lactones/chemistry , Mesylates/chemistry , Organometallic Compounds/chemistry , Oxazepines/chemical synthesis , Catalysis , Cyclization , Esters , Molecular Structure , Oxazepines/chemistry , StereoisomerismABSTRACT
Bicyclodihydrosiloles 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,ß-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.
ABSTRACT
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.
