The chemistry of terpenes. Part XVI. Some oxidation products of β-pyronene

Abstract

Oxidation of β-pyronene (1,2,6,6-tetramethylcyclphexa-1,3-diene)(1) with Brown's chromic acid reagent gave 4-hydroxy-3,4,5,5-tetramethylcyclohex-2-enone (5), which was reduced to cis-(7) and trans-1,2,6,6-tetramethylcyclohex-2-ene-1,4-diol (8) The cis-isomer (7) was also obtained by reduction of the peroxide (9) formed on photo-oxidation of β-pyronene. The diols (7) and (8) and 1,6,6-trimethyl-2-methylenecyclohex-3-enol (12) were obtained when β-pyronene was oxidised in ether with monoperphthalic acid. Oxidation of β-pyronene with peraceticacid in acetic acid, and with perbenzoicacid in chloroform gave the dienol (12), and as main products, respectively the 4-acetate (14) and 4-benzoate (15) of the cis-diol (7). Oxidation of β-pyronene in ether with perbenzoic acid gave the epoxide (16) as main product, the benzoate (15), and the dienol (12). Pyrolysis of the diol (8) over pyridine-treated alumina gave 1,2,3,4-tetramethylbenzene (13) and 2,2,6,6-tetramethylcyclohex-3-enone (18) which was also the major product of the similar pyrolysis of the dienol (12). The hydroxy-ketone (5), which has the same ring structure as abscisin II [5-(1-hydroxy-2,6,6-trimethyl-4-oxocyclohex-2-enyl)-3-methylpenta-2,4-dienoic acid](6), lacks the letter's growth regulatory properties.