1. Efficient synthesis of unsaturated seven-membered rings by an entropy/strain reduction strategy: 2,7-dihydro-1H-azepines, -oxepines, -thiepines, -1H-phosphepine and 1,3-cycloheptadienes James G. Walsh,Patrick J. Furlong,Declan G. Gilheany J. Chem. Soc. Chem. Commun. 1994 67