Tetralones Subject

Fig (6)The transformation of the tetralone (42) to the ester (45) is described. Its tranformation to the tricyclic ketone (46) involves aromatization, subjection to Grignard reaction and intramolecular cyclisation and oxidation. Its conversion to diazomethylketone (48) is carried out in three steps and this on acid catalysed cyclisation yields the enedione (49), which is converted to methy ( )-methylpisiferate (5) by standard organic reactions. 

Fig (IS) Tetralone (123) is prepared from 2,7-dim ethoxy napthalene (120) using the standard organic reactions. It is caiboxymethylated with dimethylcarbonate. The resulting compound (124) on subjection to Michael condensation yeilds tricyclic ketone (125) which on methylation followed by thioketalisation produces (128). This on desulfurisation with Raney nickel is converted to (129). 

Methoxy-a-tetralone (137), which on formylation at room temperature followed by treatment with n-butanethiol in presence of p-toluenesulfonic acid gave the compound (138), which was converted with lithium dimethylcopper and acetic anhydride to (139). Subjection of (139) to dehydrogenation, hydrolysis and methylation, respectively, yielded (140) which was converted to tetralone (141) by reduction, hydrolysis and methylation of pyralidine enamine. Alkylation of (141) with 2-... 

Baneijee et al.66 have developed an alternative synthesis of the compound (129) whose utility in synthesis of Mansonone F (120) has been reported by Suh and collaborators.65 This is described in Scheme 13. Tetralone (127) was reduced with sodium borohydride to alcohol which on alkylation with benzyl chloride produced benzyl derivative (132). Its conversion to (133) was attempted by treatment with boron tribromide in dichloromethane. C ompound (133) (characterized b y m ass s pectroscopy) was obtained in poor yield. The major product was the diol (134), whose structure was confirmed by spectral data. It indicates that the demethylation was accompanied by debenzylation. Treatment of diol (134) with triethyl orthoformate and aluminium chloride afforded aldehyde (135) which was subjected to catalytic hydrogenation to produce compound (136). It was transformed to ketone (137) by oxidation and then made to react with methylmagnesium bromide in ether. The resulting tertiary alcohol on heating with p-toluenesulfonic acid in toluene for 24 hr produced the naphthalene (129) in 78% yield. 

Scheme 13 Reduction of tetralone (127) with sodium borohydride afforded alcohol, which was benzylated to obtain the derivative (132), which on treatment with boron tribromide in dichloromethane yielded this diol (134) in major proportion. It was converted to compound (136) by treatment with triethyl orthoformate and then catalytic hydrogenation. Oxidation of (136 and on subjection of the resulting ketone with methylmagnesium bromide followed by heating with p-toluensulfonic acid in toluene produced compound (129).

The effect of ortho- and weto-substitution in the above-mentioned intramolecular Buchner reactions has been examined. When the 2-methoxy-substituted diazoketone 32 is subjected to rhodium(II) acetate catalysis, a single cycloheptatrienone 34 is obtained in 94% yield.This result is consistent with the outcome of the rhodium(II) trifluoroacetate-catalyzed intermolecular reaction of ethyl diazoacetate with anisole, which yields no product arising from addition of the ketocarbenoid on the most hindered site of the anisole. Dihydroazulenone 34 rearranges to tetralone 36 under acidic conditions, and isomerizes to the conjugated ketone 35 under basic conditions. It is interesting that the catalyzed decomposition of the para-methoxy derivative 37 provides exclusively 6-methoxy-2-tetralone 40 with no trace of the putative trienone 39. ... 

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