It is shown that the cyanoethylation of 3β-acetoxy-21-methyl-5α-pregn-17-en-21-one results in part in the addition of acrylonitrile to the γ-position, with concomitant cyclization, and that therefore the cyclo-γ-cyanoethylations of α,β-unsaturated carbonyl compounds reported previously were not confined to aldehydes. However, the main reaction products of the conjugated ketone were α-cyanoethylated derivatives. A variation of the reaction time did not affect the proportion of α- and γ-cyanoethylated products; the implications of this finding on mechanistic considerations are discussed; in particular, an explanation based on the assumption of an equilibrium between reactants and α- and γ-cyanoethylated products is ruled out. It is shown that the γ-additions observed, particularly in the case of α,β-unsaturated aldehydes, are not due to steric hindrance, neither to an abnormal charge distribution in the anion. It is further shown that in the presence of base the propionitrile moiety of oxygen-cyanoethylated α,β-unsaturated aldehydes with a suitable geometry is transferred to the γ-position of the original aldehyde and that cyclization occurs so that the same products are obtained from such cyano-enol ethers as in the direct cyanoethylation of the free aldehydes. On the basis of this finding, a mechanism for the cyclo-γ-cyanoethylations of α,β-unsaturated carbonyl compounds, involving such a transfer reaction, can be tentatively proposed.
这段文字的中文翻译如下:
研究表明,对3β-乙酰氧基-21-甲基-5α-孕-17-烯-21-酮进行
氰乙基化反应,在一定程度上导致
丙烯腈加到γ位,同时发生环化反应,因此先前报道的α,β-不饱和羰基化合物的环-γ-
氰乙基化反应并不仅限于醛类化合物。然而,这种共轭酮的主要反应产物是α-
氰乙基衍
生物。反应时间的变化并不影响α-和γ-
氰乙基产物的比例;这一发现对于机理的考虑有重要意义;特别是,基于反应物和α-和γ-
氰乙基产物之间存在平衡的假设的解释被排除。研究表明,观察到的γ-加成,特别是在α,β-不饱和醛类化合物的情况下,并非由于立体位阻,也不是由于阴离子中存在异常的电荷分布。进一步研究表明,在碱存在的情况下,具有适当几何构型的氧-
氰乙基化的α,β-不饱和醛类化合物的
丙腈基团会转移到原始醛类化合物的γ位,并且发生环化反应,从而从这种
氰基烯醇醚中得到与直接
氰乙基化自由醛类化合物相同的产物。基于这一发现,可以初步提出涉及这种转移反应的α,β-不饱和羰基化合物的环-γ-
氰乙基化反应机理。