2-[(1E ,3E )-4-Arylbuta-1,3-dien-1-yl]-4H -chromen-4-ones as Dienes in Diels-Alder Reactions - Experimental and Computational Studies: 2-[(1E ,3E )-4-Arylbuta-1,3-dien-1-yl]-4H -chromen-4-ones as Dienes in Diels-Alder Reactions - Experimental and Computational Studies