Preparation of unsaturated α,α-dichloro acid chlorides and intramolecular [2 + 2] cycloadditions of the α-chloroketenes reductively generated from them. Effect of double bond geometry on the cycloaddition
作者:Barry B. Snider、Marleen Walner
DOI:10.1016/s0040-4020(01)80143-5
日期:1989.1
Reduction of unsaturated α,α-dichloracid chlorides with zinc dust in THF at reflux generates an unsaturated α-chloroketene which undergoes an intramolecular [2 + 2] cycloaddition in good yield. This reaction can be used with three carbon tethers to prepare 5-chlorobicyclo[3.2.0]heptan-6-ones and 1-chlorobicyclo[3.1.1]heptan-6-ones but fails with larger tethers. Unsaturated ketenes 18 and 28, with a
在THF中,在回流下用锌粉在锌粉中还原不饱和α,α-二氯氯化物,生成不饱和α-氯代乙烯酮,该分子以较高的收率进行分子内[2 + 2]环加成。该反应可以与三个碳系链一起使用,以制备5-氯双环[3.2.0]庚-6-和1-氯双环[3.1.1]庚-6-,但是对于较大的系链则失败。具有反式双键的不饱和烯酮18和28立体定向反应,以高收率得到双环[3.1.1]庚酮21和29。具有顺式-双键的不饱和烯酮12在失去立体化学的情况下反应生成19和21的2:1混合物产量不佳。的更大反应性的反式-比顺式分子内-double键[2 + 2]烯酮对比的环加成,其中分子间环加成顺-double键是更具反应性。含有氯和外亚甲基的加合物41和42可以容易地制备。加合物的还原性脱氯反应可以通过(n- Bu)3 SnH或CrCl 2来实现。在碱处理中很容易发生环收缩以得到酸48和49。