Chromium diacetate reduction

Tricarbonyl( 1 -ewrfo-allyltetralin)chromium, stereoselective alcohol to hydrocarbon reduction, 132 1,2,3-Trideoxy-D-r/fco-hex-1 -enopyranose diacetate, allyl ester reduction,... 

The methyl substituent of 2-methyl-4,8-dihydrobenzo[l,2- 5,4-. ]dithiophene-4,8-dione 118 undergoes a number of synthetic transformations (Scheme 8), and is therefore a key intermediate for the preparation of a range of anthraquinone derivatives <1999BMC1025>. Thus, oxidation of 118 with chromium trioxide in acetic anhydride at low temperatures affords the diacetate intermediate 119 which is hydrolyzed with dilute sulfuric acid to yield the aldehyde 120. Direct oxidation of 118 to the carboxylic acid 121 proceeded in very low yield however, it can be produced efficiently by oxidation of aldehyde 120 using silver nitrate in dioxane. Reduction of aldehyde 120 with sodium borohydride in methanol gives a 90% yield of 2-hydroxymethyl derivative 122 which reacts with acetyl chloride or thionyl chloride to produce the 2-acetoxymethyl- and 2-chloromethyl-4,8-dihydrobenzo[l,2-A5,4-3 ]-dithiophene-4,8-diones 123 and 124, respectively. 

Treatment of (31) with crotyl chloride-potassium carbonate in DMF afforded (33), which was converted into (34) by heating in a sealed tube. Methylation of the phenol (34) with methyl iodide-potassium carbonate gave (35). Osmic acid-sodium periodate oxidation produced the keto-aldehyde (36). Acetalization by standard methods gave the diacetal (37). Reduction of (37) with lithium in liquid ammonia and subsequent toluene-p-sulphonic acid work-up afforded (38) in a yield of 50 %. A vinylogous aldol condensation was effected with methan-olic potassium hydroxide. The resulting mixture was oxidized with chromium... 

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