A Novel Controlling Method for Regio- and Stereoselectivity in the Carbonyl-Allylation using Allylic Tin Reagents

在γ-取代烯丙基锡试剂与羰基化合物的光促进反应中，烯丙基锡试剂通过单电子转移到光激发三重态羰基化合物上，烯丙基基团主要在其α位引入羰基碳中。光诱导的α-烯丙基化立体专一地进行，例如，（E）-和（Z）-γ-烷氧基烯丙基锡试剂得到（R）-和（Z）-α-高烯丙醇。在α-烷氧基醛与α-烯基锡的反应中，通过适当的烷氧基组合，选择性地合成了syn-gamma-、anti-gamma-、syn-gamma-和syn-e-加合物四种可能的区域和立体异构体。刘易斯酸和溶剂。以MgBr_2为刘易斯酸时，α-含氧保护醛如苄基（Bn）或甲氧甲基（CH_3）等生成γ-顺式加合物，而以叔丁基二甲基硅烷基（TBS）为保护剂时，BF_3 OEt_2与α-保护醛反应生成α-反式加合物，而SnCl_4与苄基保护醛反应生成γ-顺式加合物。在InCl_3存在下，乙醇介质中，TBS保护的醛与InCl_3反应，生成γ-反加合物。因此，通过反应促进剂和醛的保护基的适当组合，可以实现羰基的区域和立体控制的烯丙基化和烯丙基化。

In the light promoted reaction of gamma -substituted allyltin reagents with carbonyl compounds, the allylic groups could be introduced predominantly at their a-position into carbonyl carbon via single electron-transfer from allylic tin reagent to the photoexcited triplet carbonyl compounds. The photoinduced alpha-allylation proceeds stereospecifically, for example, (E)- and (Z)-gamma-alkoxyallylic tin reagents give (R)- and (Z)-a-homoallylic alcohols. The photoinduced allylic 1,3-rearrangement has been also investigated in detail by direct excitation of y -substituted allyltin compounds.In the reaction between a-alkoxyaldehydes and pentadienyltin, each of the possible four regio- and stereolsomers, syn-gamma-, anti-gamma-, syn-epsilon-, and syn-e-adducts, was selectively synthesized by the use of an appropriated combination of alkoxy groups. Lewis acids, and solvents. When MgBr2 was used as Lewis acid, the protecting a-oxygenated aldehyde such as benzyl (Bn) or methoxymethyl (MOM) affoided gamma-syn-adduct, but the combination of BF3OEt2 with a-protected aldehyde by tert-butyldimethylsilyl (TBS) gave a-anti-adduct, On the other hand, SnCI4 was found to give syn-gamma-adduct in the reaction with the benzyl protected aldehyde, When the reaction of the aldehyde protected by TBS was performed in the presence of InCl3 in ethanol media, gamma-anti-adduct was produced. Thus, the regio- and stereocontrolled allylation and pentadienylation of carbonyl group could be achieved by a appropriate combination of the reaction promoter and the protecting group of aldehyde.