2,3,4,5-四取代-顺-2,3-二氢呋喃立体选择性合成方法的研究

研究了3种合成2甲氧羰基3芳基4乙酰基5甲基顺2,3二氢呋喃(7)的方法.方法1:用甲氧羰基亚甲基三苯基胂(5)与3(取代苯甲叉)2,4戊二酮(6)反应;方法2:用溴化甲氧羰基甲基三苯基胂(4)在碳酸钾存在下与戊二酮6反应;方法3(分步一锅法):三苯基胂(2)与溴代乙酸甲酯(3)加热反应,生成的产物不经分离,冷却至室温,加入碳酸钾和6继续反应.

Studies on Stereoselective Synthetic Methods of 2,3,4,5-Tetrasubstituted-cis-2,3-dihydrofurans

Three methods for The stereoselective synthesis of 2-carbomet hoxy-3-ary l-4-acethyl-5-methylcis dihydrofurans(7a_7g)were studied.The 1st met hod is proceeded t hrough the reaction of carbomet hoxy methylenet riphenylarsorane(5)with 3 substituted benzal 2, 4-pent adione(6)in benzene at room temperature for 4 h and high yield of the products 7a_7g can be obtained.The 2nd method is started from the reaction of carbomet hoxy methylt riphenylarsonium bromide(4) with K₂CO₃in dimethylet hyleneglycol at room temperature, The Ylid 5 formed reacted with 6 in sit u, excellent yield of 7 can be obtained and triphenylarsine recovered quant it at ively.The 3rd met hod is a stepw ise one pot reaction, tripheny larsine(2)and methyl bromoacetate(3)is refluxed in dimethyl et hyleneglycol for 25 h, after cooling, potassium carbonate and 6 are added in and the reaction continued at room temperature for 2d, the overall yield from starting material triph enylarsine is about 65%.Although The 1st method is a very simple process for preparing 2, 3-dihydrofuran derivatives, its application is limited due to the unst ability of Ylid 5 during its prepa ration and storage, so the last two methods seem pref erable.The structures of The products 7a_7g were confirmed by means of IR, ¹HNMR, MS and elementary analysis and their configurations were established through The coupling constants of The two protons on 2-C and 3-C atoms in The dihydrofuran ring.These reactions were alhighly stereoselective and only one kind of stereoiso mer with cis conf iguration was formed.It is notewort hy that these reactions no similar normal Wittig reaction products were detected.