FACE SELECTIVITY IN DIELS-ALDER REACTIONS OF CHIRAL DIENES CONTAINING ALLYLIC SUBSTITUENTS
FACE SELECTIVITY IN DIELS-ALDER REACTIONS OF CHIRAL DIENES CONTAINING ALLYLIC SUBSTITUENTS
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DOI：
10.1021/ja00222a022
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发表时间：
1988-07-06
影响因子：
15
通讯作者：
OVERMAN, LE
中科院分区：
文献类型：
--
作者：
FISHER, MJ;HEHRE, WJ;OVERMAN, LE
考察了6种一般结构3和4的二烯在Diels-Alder反应中的表面选择性。这些二烯被选为构象锁定的1(E)-取代的1，3-二烯的模型，在烯丙基位置含有手性中心。在除一种情况外的所有情况下，环加成反应优先发生在二烯基面与烯丙基取代基之间(参见表I)。羟基取代二烯8a与A‘-苯基马来酰亚胺(NPM)的环加成反应在甲苯中有弱的同步优先反应，而在其他溶剂中有反优先反应。因此，没有发现起源于氢键以外的烯丙基杂原子取代基具有合成导向作用的证据。这些结果表明，许多5-杂环戊二烯取代的1，3-环戊二烯不会外推到含有1(E)-烯丙基取代基的1，3-二烯。这种差异很容易得到合理的解释，因为L(GB)取代的1，3-二烯的取代基在空间上接近双烯基团的双烯基团(见图3)，而5-取代的1，3-环戊二烯的环加成过渡态(见图6)的这些基团则相距很远。在二烯与乙烯基亚硫基或烯丙基醚取代的环加成反应中观察到的高反面选择性(AAG*和GT；2千卡/摩尔)归因于非键静电相互作用，这将有助于面选择性Diels-Alder反应的设计。
Face selectivity in Diels-Alder reactions of six dienes of general structure 3 and 4 was examined. These dienes were chosen as models for conformationally locked 1 (E)-substituted 1, 3-dienes containing a center of chirality at the allylic position. In all cases but one, cycloaddition occurred preferentially from the diene face anti to the allylic substituent (see Table I). Cycloaddition of the hydroxy-substituted diene 8a with A’-phenylmaleimide (NPM) occurred with a weak syn preference in toluene, but with an anti preference in other solvents. Thus, no evidence for a syn directing effect of an allylic heteroatom substituent whose origin is other than hydrogen bonding was found. These results demonstrates that the syn cycloaddition preferences observed with many 5-heterosubstituted1, 3-cyclopentadienes will not extrapolate to 1, 3-dienes containing 1 (E)-allylic substituents. This difference is easily rationalized by the fact that the substituent of a l (£)-substituted 1, 3-diene is spatially close to the dienophile in the syn-endo transition state (see Figure 3), while theendo transition state for cycloaddition of a 5-substituted 1, 3-cyclopentadiene (see Figure 6) has these groups far apart. The high anti face selectivity (AAG*> 2 kcal/mol) observed in cycloadditionsof dienes with vinyl sulfinyl or allylic ether substitution is attributed to nonbonded electrostatic interactions and will be useful in the design of facially selective Diels-Alder reactions.