Pergamon 0040-4039(95 )01145 -5 Tetrahedron Letters, Vol. 36, No. 32, pp. 5735-5736, 1995 Elsevier Science Ltd Printed in Great Britain 0040-4039/95 $9.50+0.00 Chromium-Mediated Benzylic Oxidations by Sodium Percarbonate in the Presence of a Phase Transfer Catalyst. Jacques Muzart*, Samla Ai't-Mohand Unit~ de Recherche "R~arrangementsThermiques ct Photochimiques"Associ6eau C.N.R.S., Universit~ de Reims Champagne-Ardenne,BP 347, 51062 Reims, France Abstract: In the presence of catalytic amounts of (n-Bu3SnO)2CrO2, Adogen 464 and p- toluenesulfonic acid, be~azylic methylene groups m-eeffectively oxidized into alcohols and ketones by sodium percarbonate in refluxing acetc~itrile. Sodium percarbonate (Na2CO3" 1.5 H202 = SPC) is a peroxygen compound available at a low price and extensively used in the detergent industry as a bleaching or antiseptic agent. 1 Thus, SPC, which can be considered as a "dry carrier" of hydrogen peroxide, is an attractive oxidizing agent. Its use is beginning to emerge as a useful reagent in organic synthesis. 2 As this oxidant has only previously been studied in the absence of metal catalysts, its potential scope could be enormous. 3 Recently, we have reported that SPC oxidizes effectively allylic and benzylic alcohols in refluxing 1,2-dichloroethane (DCE) when the reaction is carried out in the presence of catalytic amounts of both pyridinium dichromate (PDC) and Adogen 464. 4 We have subsequently demonstrated that the main role of the phase transfer catalyst is to favour the solubilization of the dichromate in the organic solvent. 5 We have now observed that SPC can achieve benzylic oxidations in fair yields under chromium-catalysis. Preliminary investigations have been carried out using indane (1) as substrate. OH 0 ~ Adogen 464 10.2equiv.) I~ + + catalyst (0.1 equiv.) solvent,80-83°C,20 h 1 2 3 O 4 O Under experimental conditions similar to those we employed for the oxidation of alcohols, 4 a mixture of indan-l-ol (2), indan-l-one (3) and indan-l,3-dione (4) was obtained, 3 being the major product (Table, entry I). Switching from DCE as solvent to acetonitrile increased the yields (entry 2) while the use of benzene or chlorobenzene was greatly detrimental to the conversion of 1 (entries 3 and 4). Replacing PDC with (n- Bu3SnO)2CrO26 as catalyst improved the conversion and yields particularly when MeCN was employed as solvent (entries 5 and 6). A fair conversion was also achieved with (Ph3SiO)2CrO27 in MeCN where the ratio of 2/3 was also increased (entry 7). The mediation of the oxidation by chromium species was clearly exemplified since in their absence a sluggish reaction and low yields of the oxidized products resulted (entry 8). Under the present conditions, metal-catalysis with RuCI3, Mn(acac)3 or MoO2(acac)2 was less successful than with the chromium-compounds (entries 9 to 11). The conversion was also greatly reduced in the absence of Adogen 464 (entry 12). We have previously ascertained that the presence of small amounts of p-toluenesulfonic acid in chromium- catalyzed propargylic oxidations by tert-butyl hydroperoxide is beneficial. 8 In the present study, we have also observed that co-catalysis by TsOH favours better efficiency of the chromium-assisted benzylic oxidation of 1 by SPC in MeCN, but not in DCE (entries 13 to 16). 5735