双烯与烯烃通过协同机理合成六元环的方法及Diels-Alder反应是环加成中最重要的方法，已经得到深入的研究。

通过双烯Diels-Alder反应制备环烯

一般的情况下，双烯上带富电子的基团，而亲双烯体则带吸电子基团比较容易环加成, 大部分情况下主要生成endo构型，而exo构型则较少。用前线轨道理论可以很好的解释Diels-Alder反应的化学反应性和选择性。

双烯的C1位有富电子基团容易生成相邻产物，而双烯的C2位有富电子基团容易生成对位产物。(J. Sauer, Angew. Chem. Int. Ed. Engl. 1967,6, 16.)

Lewis酸(ZnCl2, AlCl3, MeAlCl2, Et2AlCl,BF3, TiCl4, SnCl4) 可以很好的催化Diels-Alder反应，使反应在低温下顺利进行，还可以提高反应的区域选择性和立体选择性。(T. Inukaiand Kojima, J. Org. Chem., 1966,31, 1121)

实例一

To a -78 oC solution of diene 1 (0.14 g, 0.268 mmol)and α-acetoxy acrolein 5a (0.117 g, 1.03 mmol) in 3:1 toluene: CH2Cl2(4 mL) was added to SnCl4(37.6 μL, 0.322 mmol) dropwise. The reaction was stirred at -78 oC for 1 h and was then quenched by addition of a saturated solution of NaHCO3(2 mL). The mixture was diluted with ether and 1N HCl. The aqueous layer was extracted with ether (3 X 10 mL). The combined ethereal extracts were dried over MgSO4, filtered and concentrated to dryness. The crude product was purified by flash chromatography (5:1 hexanes-ether) to give 0.154 g (90% yield) of product 6a (endo: exo 96:4).

Reference: J. Am.Chem. Soc., 1997, 119, 7402.