Carboxymethylation ofp,alpha;beta;beta;-tetramethylstyrene by manganese(III) acetate. Reductive cyclization during treatment of the derived gamma;-aryl-gamma;-lactone with polyphosphoric acid to give 4-isopropyl-7-methyl-1-tetralone

摘要

1975 1235Carboxymethylation of p,app-Tetramethyistyrene by Manganese( 111)Acetate. Reductive Cyclization during Treatment of the Derived y-Aryl-y-lactone with Polyphosphoric Acid to give 4-lsopropyl-7-methyl-l-tetraloneBy Ramachandra B. Mane and G. S. Krishna Rao,rsquo; Department of Organic Chemistry, Indian Institute ofScience, Bangalore 56001 2, IndiaOxidation of p, apP-tetramethylstyrene (I) with manganese( 1 1 1 ) acetate gave a lactone mixture in which the presenceof 4-isopropyl-4-p-tolyIbutan-4-olide (V) as the major component was inferred from its n.m.r. spectrum. Theformation of this lactone (V) is attributed to the addition of carboxymethyl radical from manganese(tl1) acetateto a-isopropyl-p-methylstyrene (11). arising from (I) by double-bond isomerisation. Treatment of the lactonemixture with polyphosphoric acid furnished in high yield 4-isopropyl-7-methyl-1 -tetralone (VIII), identified byindependent synthesis.This cyclization involves reduction by hydride transfer.THE recently discovered carboxyniethylation of olefins,including styrenes, by manganese(II1) acetate leading toy-lactonesrsquo;l and our interest in its application to terpen-oid transformationsJ2 prompted us to examine the actionof manganese (111) acetate on 9, ap p-tetramethylstyrene(I). We hoped thus to obtain 3,3,4-trimethyl-4-$-tolyl-butan-4-olide (111), as the corresponding acid (IV) is akey intermediate in the synthesis of the naturally occur-ring scsquiterpenoid ketone, p-~uparenone.~Y0 ( Y T ) 0(Y)Grignard reaction of isopropylmagnesium iodide with$-methylacetophenone followed by dehydration furnishedthe tetramethylstyrene (I), the various methyl groups ofwhich were clearly assigned from its 1i.m.r.spectrum, inthe light of Sternhellrsquo;s work on trimetliylstyrene~.~The reaction of the styrene (I) with manganese(II1)acetate furnished a y-lactonic product (Amxe 1776 cm-l)which proved to be an inseparable mixture (overlappingbands obtained on preparative t .l.c. with various solvent1 (a) J . B. Bush, jun., and H. Finkbeiner, J . Amer. C h i n . SOC.,1968, 90, 5903; (b) E. I. Heiba, R. M. Dessau, and W. I. Koehl,ibid., p. 5905.2 M. E. N. Nambudiry and G. S. Krishna Rao, Indian J ..Chcn2., i n the press.combinations). From the isopropylmethyl doublets inthe n.m.r.spectrum of this mixture and their intensity6 0.88 (dd, J 7 Hz), the presence in major amount of ay-lactone, probably (V) besides the lactone (111), wasinferred. The formation of the lactone (V) can beexplained on the basis of addition of the carboxymethylradical arising from manganese(II1) acetate t o thestyrene (11) formed from (I) by double-bond isomeris-ation. In order to confirm the presence of this lactoneY YIC02H(V), we treated the lactone mixture with polyphosphoricacid in the hope of isolating the naphthol (VII), formedfrom (V) by cyclodehydration which could occur via theketol (VI). However the product was in fact the tetra-lone (VIII) (Arnx 1678 cm-l), obtained in high yield andidentified from its n.m.r.spectrum and comparison withmaterial synthesised independently as follows.Methyl 4-oxo-4-~-tolylbutyrate (IX) on inverse3 R. B. Mane and G. S. Krishna Kao, J.C.S. Perkin I , 1973,G. F. Newsoroff and S. Sternhell, Austral. J . Ckem., 1966,19,S. Dev, J . Indian Citern. SOC., 1948, 25, 315.1806.16671236 J.C.S. Perkin 1Grignard reaction with isopropylmagnesium iodide andwork up with ice-cold dilute hydrochloric acid gave theunsaturated acid (X) . Its reduction (nickel-aluminiumalloy-sodium hydroxide) to the saturated acid (XI)followed by its cyclization with polyphosphoric acid gave4-isopropyl-7-me thyl-l-tet ralone (VI I I), ideiit ical (i. r.spectra and mixed m.p.s of 2,4-dinitrophenylhydrazones)with the tetralone originating from (I).The formation of(VIII) from the other isomeric y-lactones (111) and itsisomer, 3,4,4-t rimet hyl-3-$-tolylbutan-4-olide, resultingfrom direct addition to the styrene (I) is mechanisticallyimprobable.The formation of the tetralone (VIII) from the y-lactone mixture presumably occurs by hydride transferto the C-4 carbocation derived from the tertiary carbinol(VI). There are precedents for similar reductions ofcarbocations by hydride transfer during treatment withpolyphosphoric acid, although the hydride donor does notin all cases appear to have been identified.' In certainheterocyclic systems also, acid-catalysed intermolecularhydride transfer by disproportionation has been ob-served.*The intervention of the lactone (V) in the path(I) __t (11) + (V) + (VIII) was independentlydemonstrated as follows.The unsaturated acid (X) waslactonised (by acetic acid-concentrated hydrochloricacid) to give a two-component mixture A,, 1775 (y-lactone) and 1760 cm-l (blactone), expected to be a mix-ture of (V) and (XII), formed by lactonisation at thebenzylic carbon and the isopropyl carbon, respectively, of(X) which could not be separated. Treatment of thelactone mixture with polyphosphoric acid affordedneutral material consisting of two components, the majorone of which (separated by preparative t.1.c.) was identi-cal with 4-isopropyl-7-met h yl-1 -tetralone (VII I).The investigation thus reveals double-bond isomeris-ation of a trisubstituted styrene during manganese(II1)acetate oxidation and carbocation reduction duringtreatment of a y-alkyl-y-aryl-y-lactone with polyphos-phoric acid.EXPERIMENTALp,orpp-Tetvamet~yZstyvene (I) .-A solution of p-methyl-acetophenone (25 ml) in dry ether (50 ml) was added drop-wise with stirring a t room temperature to isopropylmag-nesium iodide from isopropyl iodide (29 ml), magnesium(7 g), and dry ether (50 ml).The solution was then stirredfor 1 h, left overnight, and added to crushed ice (160 g) andconcentrated hydrochloric acid (20 ml) . The organic layerwas separated and the aqueous portion extracted twice withether. The residue obtained on removal of ether was re-fluxed with ethanol (150 ml) and concentrated hydrochloricacid (30 ml) for 6 h. Ethanol was removed under reducedpressure and the residue extracted with ether.The crudeproduct, containing some unchanged ketone, was treatedwith 2,4-dinitrophenylhydrazine reagent (7 g) and steam-distilled. Distillation of the steam-volatile hydrocarbongave the pure styrene, b.p. 115-117" a t 43 mmHg (24 g),(CC14) 1.56 (3H, m, p-Me cis to ring), 1.77br (3H, s, p-MeS. Dev, J . Indian Chem. SOC., 1948, 26, 323, and referencescited therein.trans to ring), 1.90 (3H, ni, or-Me), 2.30 (3H, s, ArMe), and6-95 (4H, ni, ArH) (Found: C, 90.0; H, 10.0. CI2H,,requires C, 89.9; H, 10.l~o).Oxidation of the Styrene (I) with Manganese(II1) Acetate.-A mixture of the styrene (I) (8 g), freshly prepared mangan-ese(II1) acetate la (26.8 g), acetic acid (350 ml), acetic anhy-dride (100 ml), and potassium acetate (150 g) was refluxedunder nitrogen for 4 h.lb The mixture was cooled andpoured into water (1 1).The organic phase was extractedwith ether. Distillation of the residue (11 g) obtained onremoval of ether gave v-lactonic material (6.2 g ) , Amx-1776 cm-l, b.p. 145-160" a t 2 mmHg.Treatment of the Lactone Mixture from the Styrene (I) withPolyphosflhoric Acid : Isolation of 4-Isopropyl-7-methyl- 1-tetralone (VIII) .-The mixture of lactones (0-8 g) was stirredwith polyphosphoric acid prepared from phosphorus pent-oxide (10 g) and phosphoric acid (6 ml) at 90-100" for2.5 h. The mixture was cooled and decomposed withcrushed ice (100 g) and the product extracted with lightpetroleum. Removal of the solvent and short-path sublim-ation (135-140" a t 2 mmHg) furnished ketonic material(0.6 g), v,, (film) 1678 cm-l, 2,4-dinitrophenyZhyd~uzone,m.p. 166-167" (from ethanol-ethyl acetate), 6 (CDC1,) 0.87(3H, d, J 7 Hz, MeCMe), 1-05 (3H, d, J 7 Hz, MeCMe),2.42 (3H, s, ArMe), 1.5-2.8 (m, CH, and CH), 7.12 (2H, m,aromatic H-5 and -6), 7.92br (lH, s, H-8 peri to GO), 8.13(lH, d, J 10 Hz, 2,Cdinitrophenyl H-6), 8-35 (lH, dd, J 10and 3 Hz, 2,Pdinitrophenyl H-5), 9.11 (lH, d, J 3 Hz, 2,4-dinitrophenyl H-3), and ll.3br (IH, s, NH) (Found: C,63.1; H, 5-6; N, 14.4.C2,H2,N40, requires C, 62.8; H,5-8; N, 14.7).5-MethyZ-4-(p-tolyZ)hexanoic Acid (XI) .-An ethereal sol-ution of isopropylmagnesium iodide from magnesium (4.5 g)and isopropyl iodide (42 g) in dry ether (150 ml) undernitrogen was added dropwise at room temperature undernitrogen to a solution of methyl 4-0~0-4-(fi-tolyl)butyrate(IX) (52 g) in dry ether (125 ml) during 20 min.The mix-ture was then refluxed (4 h), left overnight, and decomposedby addition of ice-cold dilute hydrochloric acid (1:3 acid:water; 100 ml), and the ether layer was separated. Theaqueous portion was thoroughly extracted with ether. Thecombined organic extract was washed with aqueous 5sodium carbonate. The alkaline extract was washed withether, cooled, and acidified (ice-cold hydrochloric acid) togive the unsaturated acid (X) (17.5 g) as a syrupy liquid,v,, (film) 3040-2590br (OH of C0,H) and 1709 cm-l(GO of acid). To the unsaturated acid (10 g) dissolved inaqueous sodium hydroxide (1 0 ; 330 ml), nickel-alu-minium alloy powder (33 g) was added at 95" in smallportions with stirring during 2 h.Heating and stirringwere then continued for 1 h more. The Raney nickel wasfiltered off and the filtrate poured into concentrated hydro-chloric acid (330 ml) and crushed ice (ca. 160 g) to furnish thesaturated acid, b.p. 155-160" a t 2 mmHg (8.6 g) (Found:C, 76.5; H, 9.2. C14H,,0, requires C, 76.4; H, 9.1).4-lsopropyZ-7-methyZ- l-tetralone (VIII) .-(a) From thesaturated acid (XI). The acid (XI) (8-5 g) was stirred withpolyphosphoric acid from phosphorus pentoxide (17 g) andphosphoric acid (10 ml) at 95' for 30 min. Work-up asdescribed already gave the tetratofie (6 g), b.p. 135-140" at2 mmHg, v,, (film) 1678 cm-1 (GO), 6 (CCl,) 0.94 (3H,R.T. Conley and B. E. Nowak. J . Org. Chenz.. 1962,27,3196,.and references cited therein.V. N. Gogte, K. M. More, and B. D. Tilak, Indian J. Chem.,1974, 12, 327, and references cited therein1975 1237d, J 7 Hz, ;MeCRle), 0.96 (3H, d, J 7 Hz, MeCMe), 2-33 (SH,s, ArMe), 1.9-2.9 (m, CH, and CH), 7-03-7.17 (2H, m,H-5 and -6), and 7.71br (lH, s, H-8) (Found: C, 83-3; H,8.8.A solution of the acid(X) (6 g) in acetic acid (20 ml) and concentrated hydrochloricacid (20 ml) was set aside for 36 h. Acetic acid was removedi i z vucuo and the organic residue was extracted with ether.'Thc extract was washed several times with saturated aqueoussodium hydrogen carbonate to remove any unlactonisedacid. Removal of solvent furnished neutral lactonic mater-ial, b.p. 160-165" a t 2 mmHg (5 g), as a viscous yellowishoil, vmax. (film) 1775s (y-lactone) and 1750 cm-l (blactone).T.1.c. (silica gel) showed two very close spots. The lactonicC,,H,,O requires C , 83.2; H, 8.9).(b) Fvom the unsaturated acid (X).material (1.6 g) was treated with polyphosphoric acid asdescribed above and the neutral product sublimed a t 145-150" and 3mmHg (1.3 g); vmx (film) 1678s cm-l (GO).Preparative t.1.c. of the ketonic material gave two com-ponents. The major, less polar component was the tetra-lone (VIII) (i.r. spectrum).The 2,4-dinitrophenylhydrazone prepared from the tetra-lone obtained by the above procedures was identical m.p.(167") (from ethanol-ethyl acetate), mixed m.p., and i.r.(Nujol) and n.m.r. (CDCl,) spectra with the 2,4-dinitro-phenylhydrazone obtained from the tetralone formed in thereaction of the Iactone mixture arising from (I) with poly-phosphoric acid.1412616 Received, 3rd Decembev, 1974