Ring homologated ketones, synthesis

An improved synthesis of Uhle s ketone (54), a useful intermediate in ergoline synthesis, has been described,36 in which the closure of the ketone ring is accomplished by the Dieckmann reaction this route is also applicable to the homologous ketone. 

Synthesis via C14 Ketones with an Aromatic Ring A. The synthesis of the most important representatives of this group of com-poands, the ketone (85), its methyl homolog (77), and the keto ester (81) and also their saturated analogs (91), (83), and (90), is shown in Scheme 8. 

For the synthesis of the complex natural product, the terminus six-membered ketone 55 had to be transformed into an oxepane ring. For this necessary transformation, the authors were attracted by the single-carbon homologation of a pyr-anone (a sort of ring-expansion) because, in prindple, it could be used in an iterative sense at any stage of the 6-endo cydization in their poly-TH P-based synthetic approach for the synthesis of trans-fused 6,7,6 (THP-oxepane-THP) and 6,7,7 (THP-oxepane-oxepane) ring systems [28]. Treatment of ketone 55 with TMSCHN2... 

A broad variety of special aldehydes and ketones are easily accessible by Heck-type reactions with allylic alcohols and their homologs [3]. The potential for the synthesis of carbocydic structures is illustrated by the macrocyde 11 [4] which obviously is the product of a fourfold Heck reaction (Scheme 3). A domino process consisting of a double Heck reaction followed by an intramolecular Aldol condensation leads to the annulated ring system 15 [5]. 

This chapter concerns the net conversion of a C =X ir-bond (X = O and N) to various three-membered ring heterocycles. The most common such process is the conversion of an aldehyde or ketone to a homologous epoxide. These reactions will be discussed along with the analogous process which takes place on imines and related compounds. Additionally, methods to effect the addition of elements other than carbon across either unsaturated system will considered. The synthesis of thiiranes by the addition of carbon across the C—S rr-bond is the subject of a recent comprehensive review and will not be covered here. 

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