Absolute rates of bromination were measured for two series of derivatives of steroidal ketones 3, enolacetates 1 and enol methyl ether 2. Axial substituents exhibited a large effect on rates, which increased by 15,000 fold on going from (X=CH3; Y=CN) to (X=Y=H). From the bromide ion effect it was concluded that the first step (formation of an intermediate bromonium ion) was reversible and that the
测量了甾族酮3的两个系列衍生物,烯醇乙酸酯1和烯醇甲基醚2的溴化绝对速率。轴向取代基对速率表现出很大的影响,从(X = CH 3; Y = CN)变为(X = Y = H)时,轴向取代基增加了15,000倍。从溴离子效应可以得出结论,第一步(中间体溴离子的形成)是可逆的,并且第二步(卤代酮4或5或卤代缩醛8或9的形成)与第一步相比较慢。推断该中间体是高度不对称的溴离子,而不是纯的氧碳鎓离子。
Stereochimie—LII. Controle orbitalaire de la stereochimie des reactions—III
作者:C. Agami、A. Kazakos、J. Levisalles、A. Sevin
DOI:10.1016/0040-4020(80)88022-7
日期:1980.1
The respective influences of β-fluoro and β-cyano groups on the reduction of ketones by Li(t-BuO)3AlH on the stereoselectivities of the reduction with and without added cryptands, and with and without added alkye fluoride and nitrile, were compared with ab initio calculations using the frontier orbitals of analogous carbonyl compounds to give energy values.
Rearrangement of a steroidal α-hydroxyacetal: a convenient new method for the introduction of a 5α-methyl group into the steroid nucleus
作者:Andrew W. Bridge、George A. Morrison、Nicholas F. Wooster
DOI:10.1039/c39860000132
日期:——
olestane-6-spiro-2′-(1′,3′-dioxolane)(2) and its 5β-epimer (3) undergo cleavage of the acetal ring with skeletal rearrangement to give 5-(2-hydroxyethoxy)-3β-methoxy-4aα-methyl-A-homo-B-nor-5β-cholestan-4aβ-ol (5) upon treatment with MeMgl in refluxing toluene; in a second rearrangement the A-homo-B-norsteroid (5) is smoothly converted into 3β-methoxy-5-methyl-5α-cholestan-6-one (7).