Saytzeff

Although Russian Zaitsev published most of his work in German scientific journals where his name was translit erated as Saytzeff The spelling used here Zaitsev) corresponds to the currently preferred style... 

The amino functional group is not commonly encountered in steroid synthesis except perhaps in steroidal alkaloids. However, certain elimination reactions have been shown to have theoretical and limited preparative importance, largely due to the efforts of McKenna and co-workers. The Hofmann rule for 2 elimination predicts that alkaline elimination of quaternary ammonium salts will occur towards the carbon carrying the most hydrogen atoms cf. the converse Saytzeff orientation, above). In cyclohexyl systems, the requirement for diaxial elimination appears to be important, as in other 2 eliminations, and the Hofmann rule frequently is not obeyed [e.g., (116) (117)]. 

Zaitsev s name is also transliterated as Zaitzev, Saytzeff, or Saytzev. 

Dehydration. Cu(OTf)2 (0.1 equiv.) is an effective catalyst for dehydration of primary, secondary, or tertiary alcohols and of diols at 25°. The alcohol can be used neat or as a suspension in decalin or heptane. Yields are generally higher than those obtained with H2S04 or POCl3/pyridine. Saytzeff (E)-alkenes are formed predominantly. 

A study of Hofmann vs Saytzeff elimination from 2-bromooctane under soliddiquid two-phase conditions [6] shows that the 1-octene 2-octene ratio depends not only on the base used, but also on the catalyst. Aliquat is the most effective catalyst giving a 98% overall yield with a l-octene 2-octene ratio of ca. 2 1. Benzyltriethylammonium chloride catalyses a 95% conversion with a ratio of ca. 3 1 in favour of the 1-octene. Potassium hydroxide and potassium t-butoxide favour the formation of 1-octene, whereas sodium methoxide and sodium ethoxide favour the formation of 2-octene [6]. 

If there is possibility of formation of more than one alkene due to the availability of more than one 3-hydrogen atoms, usually one alkene is formed as the major produet. These form part of a pattern first observed by Russian ehemlst, Alexander Zaitsev (also pronounced as Saytzeff) who In 1875 formulated a rule which can be summarised as in dehydrohalogenation reactions, the preferred product is that alkene which has the greater number of alkyl groups attached to the doubly bonded carbon atoms. Thus, 2-bromopentane gives pent-2-ene as the major product. 

It is a general observation that, where different alkene products can arise through E2 elimination, the more-substituted alkene predominates. 2-Menthene contains a double bond with two alkyl substituents, whereas the double bond in 3-menthene has three substituents. The more-substituted alkene is termed the Saytzeff product the less-substituted alkene is termed the Hofmann product. We recommend you disregard the proper names, and think of the products in terms of more-substituted alkene and less-substituted alkene . 

This effect is relatively small and both products are formed, usually with one predominating. The more-substituted Saytzeff product typically predominates when the leaving group is small, e.g. halide. On the other hand, when there is a large leaving group present, e.g. quaternary ammonium, then steric effects... 

This elimination involves a small leaving group, so the more-substituted alkene predominates. However, E and Z isomers of this Saytzeff product are produced, and in unequal amounts. That the major product is the -alkene can be rationalized in terms of minimizing steric repulsion during the transition state. 

We do not have the same strict stereochemical requirements as in the E2 mechanism, and isomeric alkenes may well be produced. If several hydrogens are available for elimination, then the preferred product formed is the more-substituted Saytzeff alkene. 

Durch einen konformativen Effekt werden heute auch die schon lange bei E2-Reaktionen bekannten empirischen Regeln von Hofmann 68) und Saytzeff 112) erklart. Beide Regeln machen Aussagen fiber die Oricn-... 

Saytzeff, A. 2. Zur Kenntnis der Reihenfolge der Anlagcrung und Aus-scheidung der Jodwasserstoff-Elemente in organischen Verbindungen. Liebigs Ann. Chem. 179, 296 (1875). 

In dehydration and dehydrohalogenation the preferential order for removal of an H is 3°>2°> 1 (Saytzeff rule). We can say the poor get poorer. This order obtains because the more R s on the C==C group, the more stable is the alkene. The stability of alkenes in decreasing order of substitution by R is... 

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