Chatterjee, Gautam

Lahiri, Sikha

Maity, Basudev (in part)

Pal, Panchanan

Sen, P K

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Indian .Toumal of ChemistrvVol. 37B, August 1998, pp.768 - 773Studies in catalytic dehydrogenation: Part xt-Syntheses ofalkylsubstituted spirol[ 4,6]undecanes and dehydrogenation ofl-ethyl-8,9- benzospiro[ 4,6]undecaneSikha Lahiri, Panchanan Pal, Gautam Chatterjee, Basudev Maity (in part) & P K Sen*Department of Chemistry, Presidency College, Calcutta 700073Received 26 September 1997; accepted (revised) 22 April 1998Acylation of benzene with 2-alkylsubstituted cycIopentan-l, I-diacetic anhydrides gives the keto acids(2, R = Me, Et, Pr", Pri) which are converted into the desired alkyl substituted spiro[4,6]undecanes 5 by Paarhydrogenation followed by cyclisation (H1.dWolff-Kishner reduction. Catalytic dehydrogenation of l-ethyl-8,9-benzospiro[4,6]undecane 5b with Pd-C gives a complex mixture of products from which a few majorproducts like naphthalene, 2-methylnaphthalene, l-ethylnaphthalene, 1,2-dimethylnaphthalene, 1,4,6-trimethylnaphthalene, anthracene and I-methylanthracene are identified by comparative GC-mass spectra. Aplausible explanation of the formation of these products is suggested.Sengupta and Chatterjee 1,2 have extensivelystudied catalytic dehydrogenation of tetralinderivatives containing different alkyl substituentson the spirocyclopentane ring. Presence of amethyl group in the spirocyclopentane ringundergoes ring transformation duringdehydrogenation to afford methyl phenanthrene orits derivatives. However, spiran with ethyl or n-propyl substituent leads to the formation of pyreneand l-methylpyrene respectively in identicalcondition.We have synthesised several 6-alkylbenzo-cycloheptanes'' and contrary to an early report",dehydrogenation yielded a mixture of naphthaleneand its alkyl derivatives. In order to gain insightinto the mechanism of the dehydrogenationsuggested by us], we became interested in 1-tPart IX, Reference no. 8.substituted-8,9-benzospiro[ 4,6]undecane ring sys-tem. The present note deals with the synthesis ofseveral l-alkyl-8,9-benzospirof4~6]undecanes (5,R=Me, Et, Pr", Pr') and dehydrogenation studies ofl-ethyl derivative as a representative of the abovesystem.The anhydrides 1 with benzene in the presenceof anhydrous aluminium chloride furnished theketo acids 2 which on Paar hydrogenation in thepresence of Pd-C gave the reduced acids 3. 3 oncyclisation with polyphosphoric acid afforded thespiroketones 4 which finally yielded the desiredbenzospiro[4,6]undecanes 5 on Wolff-Kishnerreduction (Scheme I). The structures of thecompounds, 2-5, were confirmed by spectralanalyses.Earlier3 it was reported that 6-alkylbenzo-cycloheptanes on dehydrogenation with Pd-C at4000 in a sealed tube yielded a mixture ofcompounds of which among others, l-rnethyl-naphthalene was identified as the major product.The suggested mechanism entails that one of thetwo benzylic carbons of benzocycloheptane is lostduring the aromatisation process. In order to testthe generality or otherwise of the abovemechanism, l-ethyl-8,9-benzospiro[ 4,6]undecane5b was subjected to dehydrogenation. Accordingly,LAHrR1 et al. . ST1JDIES IN CATALYTIC DEHYDROGENATION. PART X 769Benzene +~7'~::::,...~O21 0JR COOHIQJLQcob'Y--19 5 IV oO!J 1ll::::,...8 OIl ::::,...1 OIl7 6 4 35 431-5 a b c d .R Me Et PrnPrlReagents i) Anhydrous AlCI 3ii) 10% Pd-CIH 2 , 60 lbs/psi, ethanoliii) PPAiv) NH2NH2-KOH-ethylene glycol'a) 4a was reduced by Clemmensen reduction5b was heated in a sealed tube at 380-400° with10% Pd-C for 12 hr and the product was subjectedto fractional chromatography on Brockmannalumina using light petroleum as eluent. GC massspectra of the first fraction showed the presence ofa complex mixture of at least thirty hydrocarbonsof which six hydrocarbons namely, (i) naphthalene,(ii) 2-methyl-, (iii) i-ethyl-, (iv) I ,2-·dimethyl- and(v) 1,4,6-trimethylnaphthalenes and (vi) I-methyl-anthracene were present in major amounts. Thesecond fraction also consisted of five majorproducts of which four (i-iv) were common to thefirst fraction established by the comparative GCmass spectra and Vth product was anthracene. Inthe third fraction there was present one majorproduct, 2-methylnaphthalene which was alsocommon to early fractions. Besides the majorScheme Icomponents mentioned above three morecompounds namely, phenanthrene, 9-methyl-9H-fluorene and l-methyl-9H-fluorene (vii-ix) withappreciable concentration were detected in the firstfraction by comparative GC mass spectra.It is extremely difficult to interpret theformation of all the major products from GC-massfragmentation-pattern analysis. However, attemptwas made to offer plausible explanation (Schemes11-V) for the formation of a few products present inthe complex mixture obtained after dehydrogena-tion of l-ethyl-8,9-benzospiro[ 4,6]undecane Sb.Non-equivalent nature of the benzylic C-J 0 andallylic C-l1 carbons in Sb reveals that thedehydrogenation process is initiated by thehomolytic cleavage at more than one particularbond in the cycloheptane ring, and subsequent770 INDIAN J CHEM, SEC.B, AUGUST 1998375bj+HO HjScheme II5bScheme III-,- ----- ---LAlllRI et al. :STIJDIES IN CATALYTIC DEHYDROOENATION: PART X 771~~. C~lJJ<J cca·--~ I:::::,... .j5b..00' degradationI -44----:::::,... ~ -H; +H·04- Et·~ CH3+. + l,4-dimethylnaphthalene~ + 1,4,6-trimethylnaphthalenej-,CH3: "<.-CH3·+CH3 "<.OCX"= CH3 0:)"= CH3I I:::::,... ~ :::::,... ~CH3Scheme IVcyclisation, degradation, aromatisation andisomerisation may give rise to several products.Thus, homolytic cleavage of C-I0,C-ll bond(benzylic) is ultimately expected to lead mainly totricyclic hydrocarbons, anthracene (Scheme II) andphenanthrene (Scheme III) derivatives. Thepossibility of the cleavage of the bonds other thanbenzylic ones cannot be ruled out. Accordingly, themajor products arising from the initial cleavage ofC-ll, C-5 bond are expected to be naphthalene(Scheme IV) and fluorene (Scheme V) derivatives.Attempts to dehydrogenate other spirohydro-carbons (Sa, 5c, 5d) were abandoned due tocomplex nature of dehydrogenation reaction of5bExperimen'tal ProcedureBoiling points and melting points areuncorrected. IR spectra in KBr were recorded on aPye-Unicam SP 200 G spectrophotometer (vrnaxinem"), IHNMR spectra in CDCb (unless otherwise772 lNDlAN J CHEM, SEC.B, AUGUST 1998stated) on a Varian EM-390 spectrometer usingTMS as internal standard (chemical shifts in 8,ppm) and GC-mass spectra in Hewlett Packard IIGC-MS instrument. GLC analyses were carried outon a Pye-Unicam-104 instrument and Shimadzugas chromatograph-9A using 5% SE-30 and OV -17column respectively. Carbon and hydrogenanalyses of the compounds were withinexperimental errors. Light petroleum refers to thefraction b.p. 60-80° unless stated otherwise.2-Alkylcyclopentane-l,1-diacetic acid anhy-drides 1. These were prepared by refluxing thecorresponding 2-alkylcyclopentane 1,1-diaceticacids' with acetic anhydride. The anhydrides la,lb, Ic, ld had b.p. 158°/10 mm, 170°/2 mm, 160°/1mm and 135%.2 mm respectively.Preparation of l-benzoylmethyl-l-carboxy-methyl-2-alkylcyclopentane 2 : General pro-cedure. To a well-stirred suspension of anhydrousAICh (0.26 mole) in dry and purified benzene (150mL) was added slowly a solution of the anhydride,1(0.13 mole) in the same hydrocarbon (150 mL) at5°. After stirring for 5 hr, the mixture was leftovernight, cooled and decomposed. Followingusual work-up" the corresponding I-benzoyl-methyl-l-carboxymethyl-2-alkylcyclopentane 2 isScheme Vobtained [2a : yield 83%, b.p. 175°/1 mm; IR :1680 (>C=O), 1710 (-COOH). It gave positiveDNP test; 2b : yield 79%, b.p. 195°/1 mm; IR :1670 (>C=O), 1710 (-COOH);.IH NMR : 8.10-7.30 (5H, m, Ar-H), 3.2-2.5 (4H, m, PhCOCH2 and-CH2COOH), 2.2-1.4 (9H, m, ring cyclopentanewith methylene protons) and 0.9 (3H, m,-CH2CH3); 2c : yield 90%, b.p. 185-90%.5 mm;2d :yield 89%, b.p. 195°/1 mm].Preparation of 1-(co-phenethyl)-l-carboxy-methyl-2-alkylcyclopentane 3: General pro-cedure. The keto acid 2 (0.046 mole) was reducedwith hydrogen in a Paar apparatus in ethanol (25mL) in the presence of 10% Pd-C as catalyst under60 1bs/p.s.i. The theoretical amount of hydrogen asjudged from the pressure drop was taken up in 2hr. Removal of catalyst by filtration andevaporation of solvent left the acid 3 which wasdistilled under reduced pressure. In case of 3c and3d, the reduction was carried out at roomtemperature after addition of a few drops ofperchloric acid [3a : yield 78%, b.p. 190-95°/1mm; IR ~ 1710 (-COOH); 3b: yield 80%, b.p.185%.7 mm; IR : 1710 (-COOH); 3c: yield 56%,b.p. 192%.9 mm; 3d : yield 83%, b.p. 190%.7mm].LAHIRl et al. : STUDIES IN CATALYTIC DEHYDROGENATION: PART X 773PPA cyclisation of 3: Formation of 4:General procedure. The acid 3 (0.09 mole) washeated with PPA (prepared from 265gP20S and 156mL of phosphoric acid) on a steam-bath whilestirring for nearly 1 hr where the colour of themixture turned deep brown. Decomposition of themixture with ice followed by solvent extractionand removal of the uncyclised acid by Na2C03 leftthe cyclic ketone 4, which was purified bydistillation under reduced pressure.43: Yield 79%, b.p. 160-70°11.5 mm; IR : 1685(>C=O).4b: Yield 80%, b.p. 160°/2 mm; IR : 1675(>C=O); IH NMR : 7.70 (IH, dd, ArTH peri toCO), 7.35-6.9 (3H, m, Ar-H), 3.05-2.8 (2H, m,ArCH2), 2.75-2.30 (2H, m, ArCOCH2), 2.2-1.1(11H, m, PhCH2CH2 and cyclopentane ring withmethylene protons), 0.85 (3H, t, CH2CH3). It gavepositive DNP test.4c: Yield 83%, b.p. 198°/3 mm; IR : 1685(>C=O); IH NMR : 7.80 (IH, dd, Ar-H peri toCO), 7.4-7.3 (3H, m, Ar-H), 3.1-2.9 (2H, m,ArCH2), 2.8-2.4 (2H, m, ArCOCH2), 2.1-1.1 (13H,m, PhCH2CH2 and cyclopentane ring withmethylene protons), 0.9 (3H, t, CH2CH2CH3). ItsDNP derivative had m.p. 207°.4d: Yield 85%, b.p. 160%.5 mm; IR : 1680(>C=O); IH NMR : 7.85 (IH, dd, Ar-H peri toCO), 7.5-7.2 (3H, m, Ar-H), 3.2-3.1 (2H, m,ArCH2), 2.8-2.4 (2H, m, ArCOCH2), 2.0-1.4 (10H,m, PhCH2CH2 and cyclopentane ring with CH<substitution), 1.1-0.9 (6H, dd,CH< CH3 • Its DNP derivative had m.p. 247°.CH3Preparation of l-alkyl-S,9-benzospiro[4,6]un-decane 5: General procedure. The spiran 5b-dprepared in 75-80% yields by Huang-Minionreduction of the preceding cyclic ketones 4 hadboiling points l30-32°/4 mm, l35-37%.4 mm and160°/1 mm, respectively. The ketone 421 on Huang-Minion reduction gave Sa in poor yield. However,Clemmensen reduction of 4a afforded Sa in goodyield (60%), b.p. 1400/l.5 mm. The compound Swas checked for the absence of carbonyl peak in itsIR spectrum.Dehydrogenation of Sb. The hydrocarbon Sb (2g) was heated with 10% Pd-C (0.2 g) in a sealedtube at 380-400° for 12-14 hr. On opening thesealed tube the issuing gas burnt with a blue flame.The product was extracted with ether and benzene,the solvent removed, and the residual oil subjectedto chromatographic fractionation on a Brockmannalumina column using light petroleum as eluent.The elutes, each 25 ml, were collected and all thecompounds got eluted in the first three fractions.Each fraction was subjected to GC mass analysis.AcknowledgementThe authors are thankful to Dr S N Bhattacharyaand Dr John Enriquez of William Beaumont ArmyMedical Centre, Texas, USA for GC mass spectra.One of the authors (P P) is grateful to the UGC forgranting teacher fellowship. Author (S L) isthankful to Education Department, Govt. of WestBengal for granting Research Assistantship.References1 Sengupta S C & Chatterjee D N, J Indian chern Soc, 29,1952,438;30,1953,27;31,1954,11.2 Chatterjee D N, J Arn chern Soc, 77, 1955, 5131 andreferences cited therein.3 Sen P K, Lahiri S & Das T K, Indian JChern, 238, 1984,821.4 Chakraborty P S, Indian J Chern, 10,1972,385.5 McElvain S M & Clemens David H, J Arn chern Soc, 20,1958,3915.6 Sen P K & Lahiri S, Indian J Chern, 298, 1990,741.

Studies in catalytic dehydrogenation: Part X-Syntheses of alkylsubstituted spirol[4,6]undecanes and dehydrogenation of 1-ethyl-8,9- benzospiro[4,6]undecane

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Studies in catalytic dehydrogenation: Part X-Syntheses of alkylsubstituted spirol[4,6]undecanes and dehydrogenation of 1-ethyl-8,9- benzospiro[4,6]undecane

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