Fluorene analogous derivatives

In general, the methods that were successfully employed to generate the fluorene analogs have also been used to generate the derivatives of metalloanthracenes. 

Data for the related compounds 9,9-diphenyl-9-germafluorene and 9-oxa-10-dichlorogermyl-9,10-dihydroanthracene, are, however, less easily interpreted. Ring planarity is forced upon the fluorene derivative by the absence of a bridging atom at the 9 position of the anthracene skeleton, thereby affording the most favorable molecular architecture for heteroatom it bond participation. Contrary to expectation, however, the exocyclic Ge—C bonds are shorter than the endocyclic analogs (Table III), casting doubt upon the reliability of the data (68). 

Fluorene has been reported to afford the 3,9a-dihydro product, but it is almost certain that this is the 2,4a-dihydro isomer (55 = 1) by analogy with biphenyl. 9,10-Dihydrophenanthrene (56) is reduced as expected to (55 n = 2), but spontaneously reverts to the starting material on standing. These systems do not require the presence of alcohol for reduction and it is consequently possible to alkylate the intermediate anions with alkyl halides, as (56) gives (57). These products are much more stable and structural analysis is simplified accordingly oxidation of the doubly allylic methylene occurs readily to afford the dienone (58 Scheme 7). Dienones of this type have potential as intermediates for the synthesis of natural products. Anthracene and phenanthrene are both readily reduced in the central ring to form the 9,10-di-hydro derivatives as might be expected, but to avoid further reduction it is necessary to have an iron salt present. Further examples are reviewed elsewhere. ... 

A number of sensitive substances can be advantageously reduced by aluminum amalgam since the reaction medium can in this case easily be kept exactly neutral. It is often possible to reduce only one of the conjugated double bonds of fulvenes and indene and fluorene derivatives of analogous structure.27 The process is particularly suitable for hydrogenation of unsaturated esters28,29 that might be hydrolysed in alkaline solution. 

The halogen-metal exchange reaction has been used almost exclusively for the formation of dithienylmethanes lithiated at thiophene /(-positions these derivatives give acceptable yields of aldehydes77 on reaction with dimethylformamide and of acids on carbonation.66 Particular use has been made of bis-J -lithiated compounds for the preparation (via oxidative coupling) of thiophene analogs of fluorenes.3,67 The synthesis of cyclopenta-[ 1,2-b 4,3-b]dithiophene (67) is typical (Eq. 23). 

The above-described thermal degradations afford an insight into the molecule of cevine that centers about the nitrogen atom. The formation of the typical 2-ethyl-5-methylpyridine as w ell as its hexahydro derivative indicate that the nitrogen-containing moiety of cevine is closely related to the analogous portion of other Solanum and Veratrum alkaloids. Less easily interpretable is the formation of 1,2-benzohydrindane as well as the numerous fluorene derivatives. It is nevertheless not improbable that the carbon skeleton of cevine is similar to that of veratramine and of jervine. 

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