
TY  - JOUR
A1  - Collins, DJ 
A1  - Fallon, GD 
A1  - Skene, CE 
T1  - Synthesis of 6-Methoxy-2-methyl-2-[(1'-methyl-2',5'-dioxocyclopentyl)methyl]-3,4-dihydro-naphthalen-1(2H)-one: Its Novel Base-Catalyzed Rearrangement to a Hydrophenanthrene Keto Acid
JF  - Australian Journal of Chemistry
JO  - Aust. J. Chem.
Y1  - 1994
VL  - 47
IS  - 4
SP  - 623
EP  - 648
KW  - 
UR  - https://doi.org/10.1071/CH9940623 
N2  - Reaction of 2-dimethylaminomethyl-6-methoxy-3,4-dihydronaphthalen-1(2H)-one (7) with 2-methylcyclopentane-1,3-dione gave 64% of 6-methoxy-2-[(1&#8242;-methyl-2&#8242;,5&#8242;-dioxocyclopentyl)-methyl]-3,4-dihydronaphthalen-1(2H)-one(6a), which with 1 equiv. of ethylene glycol in refluxing benzene in the presence of 4-toluenesulfonic acid yielded a diastereomeric mixture of the 2&#8242;,2&#822;-ethylenedioxy derivatives (13a,b); the major diastereomer (13a) was shown to have 1&#8242;SR,2RS stereochemistry by X-ray crystallography. With an excess of ethylene glycol and prolonged reflux the triketone (6a) underwent aldol cyclization/acetalization to give 9,9,12,12-bis(ethylenedioxy)-3-methoxy-8-methyl-5,6,8,9,10,11-hexahydro-8,11-methano-7H-cyclohepta[a]naphthalene (19). With pyridinium 4-toluenesulfonate as catalyst, aldol cyclization was avoided, and the tri-ketone (6a) afforded 2-[(2&#8242;,2&#8242;,5&#8242;,5&#8242;-bis(ethylenedioxy)-1&#8242;-methylcyclopentyl)methyl]-6-methoxy-3,4-dihydronaphthalen-1(2H)-one (15). The triketone (6a) and its monoacetal (13a,b) were susceptible to reverse Michael cleavage in reactions with nucleophiles under either acidic or basic conditions. Methylation of the keto diacetal (15), followed by acid hydrolysis, gave 6-methoxy-2-methyl-2-[(1&#8242;-methyl-2&#8242;,5&#8242;-dioxocyclopentyl)methyl]-3,4-dihydronaphthalen-1(2H)-one (6b); 2-[(2&#8242;,2&#8242;-ethylenedioxy-1&#8242;-methyl-5&#8242;-oxocyclopentyl)methyl]-6-methoxy-2-methyl-3,4-dihydronaphtha - len-1(2H)-one (32), resulting from incomplete hydrolysis, was shown to have 1&#8242;RS,2RS stereochemistry by X-ray crystallography. The triketone (6b) underwent a novel base-catalysed rearrangement reaction to give 7-methoxy-2&#958;,10a-dimethyl-3-oxo-1,2,3,9,10,10a-hexahydrophenanthrene-4-acetic acid (33) which readily afforded the corresponding enol lactone (35). 
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