Preparation of 2,3-dihydrofurans via a double allylic substitution reaction of allylic nitro compounds.

A one-step conversion of allylic nitro compounds to substituted 2,3-dihydrofurans has been developed. Allylic nitro compounds, which are readily available from nitroalkenes and formaldehyde, underwent a double allylic substitution reaction catalyzed by a palladium complex to give 2,3-dihydrofurans in good yield.

A radical cascade cyclization to prepare dihydrothiophenes induced by thiyl radicals as sulfur biradical equivalents.

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.

Preparation of optically active bicyclodihydrosiloles by a radical cascade reaction.

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.

Total synthesis of ent-calystegine B4 via nitro-Michael/aldol reaction.

Optically active ent-calystegine B4 was prepared in 13 steps from commercially available chiral L-dimethyl tartrate. The synthesis was achieved by the Michael addition and the aldol reaction of nitromethane to form cycloheptanone in a stereoselective manner. Reduction of the nitro group in the presence of Boc(2)O accomplished an efficient conversion to amino cycloheptanone, which readily afforded the desired ent-calystegine B4.