Nomenclature ketenes

Ketenes. Derivatives of the compound ketene, CH2=C=0, are named by substitutive nomenclature. For example, C4Hc,CH=C=0 is butyl ketene. An acyl derivative, such as CH3CH2—CO—CH2CH=C=0, may be named as a polyketone, l-hexene-l,4-dione. Bisketene is used for two to avoid ambiguity with diketene (dimeric ketene). 

The answer is both For the Li enolate, the usual rule makes OU of lower priority than oMe, so it s E, while the silyl enol ether (or silyl ketene acetal ) has OSi of higher priority than OMe, so it s Z. This is merely a nomenclature problem, but it would be irritating to have to reverse all our arguments for lithium enolates simply because lithium is of lower atomic number than carbon. So, for the sake of consistency, it is much better to avoid the use of Eand Z with enolates and instead use cis and trans, which then always refer to the relationship between the substituent and the anionic oxygen (bearing the metal). 

In this context, the E- and Z-nomenclature of ester enolates and silyl ketene acetals refers to their geometries where the carbonyl oxygen given highest priority irrespective of priority by CIP Cahn-Ingold-Prelog) rules. 

Because of the higher priority give to sulfur, the Z monothioketene acetal derived from the corresponding monothioester is mechanistically equivalent to the ketene acetal derived from an ester. Care must be taken when comparing the results from monothioketene acetals with the results from ketene acetals to avoid confusion as a result of the nomenclature inversion. 

An apparently similar reaction to the Arndt-Eistert process is the homologization of aldehydes and ketones by diazomethane. In the lUPAC nomenclature of transformations (1989 c), both are methylene insertions, but the homologization of aldehydes and ketones does not involve a carbene or ketene intermediate. We discussed it therefore in Section 7.7 in the context of dediazoniations via diazonium ions and carbocations. It is worthwhile to draw attention to the early work of Wolff, as mentioned at the beginning of this section. He discussed in one of his early papers the striking fact that, in boiling water, diazoacetophenone yields the expected (at least at that time) product of a hydroxy-de-diazoniation, but, in the presence of silver... 

After some preliminary discussion of history and nomenclature, the review will briefly cover issues of rearrangement temperature, substituent effects and catalysis. Transition state stracture as determined by isotope effects combined with theoretical studies will then be described. Stereochemical aspects of the reaction will be examined in detail with accompanying examples. The remainder of the chapter will describe the various methods of ketene acetal formation, structural variety in the allyUc ester substrates and apphcations to natural product synthesis. The presentation of the material is somewhat arbitrary, and indeed most examples could well have been placed under more than one sub-heading. 

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