Indian Journal of Chemistry Vol. 4 1B , March 2002, pp. 596-597

One-pot synthesis of dimethyl 8,8-dimethyl-6, l O-dioxo-3-phenylspiro[4.5]deca-2-ene- l ,2-dicarboxylate mediated by vinyltriphenylphosphonium salt

Ali Ramazani* & Ehssan Fotouhi-Ardakani

Chemistry Department, Zanjan University, P. O. Box 45 1 95-3 13 , Zanjan, Iran

Received 9 June 2000; accepted (revised) 12 July 2001

Protonation of the highly reactive I : 1 intermediate produced in the reaction between dimethyl acetylenedicarboxylate and triphenylphosphine by 2-(2-oxo-2-phenylethyl)-S,S-dimethyl-1 ,3-cyclohexanedione 2 leads to vinyltriphenylphospho­nium salt, which undergoes an intramolecular Wittig reaction to produce the title compound 6 in fairly good yield.

�piro[4.5]decane carbon skeleton compounds are im­)ortant carbocycles in bio-organic chemistry and are )resent in many natural products and pharmaceuti­;als. I -3 There have been reported many studies on the ;ynthesis of the carbocyclic spiro[4.5]decane ring ;tructure.4-6 Alkenylation of carbonyl compounds is )ne of the most important methods in organic synthe­;is and has found widespread application in synthetic xganic chemistry,4.7 especially for the synthesis of natural products.8 A well known method for achieving :llkenylation is the Wittig reaction.9 fl -Additions of nucleophiles to the vinyl group of vinylic phospho­nium salts leading to the formation of new alky­lidenephosphoranes has attracted much attention as a very convenient and synthetically useful method in xganic synthesis, 'o particularly for the synthesis of heterocyclic compounds. I I . 1 2. 1 3 Recently, we have es­:ablished a heterocyclic synthesis using a novel ap­Jroach to vinylphosphonium salts. I I . 1 2 Herein we de­;cribe a facile one-pot synthesis of dimethyl 8,8-jimethyl-6, l O-dioxo -3 -phenylspiro [4.5]deca-2-ene­l ,2-dicarboxylate 6 in fairly good yield.

Results and Discussion Many examples are known in which a carbocyclic

alkene is formed from a phosphorane connected with a carbonyl group by a carbon chain.9• 10• 14 Thus, com­pound 6 may be considered as product of an intra­molecular Wittig reaction. Such addition-cyclization product apparently result from initial addition of triphenylphosphine to the acetylenic ester and con­comitant protonation of the 1 : 1 adduct, fol lowed by attack of the anion of 2-(2-oxo-2-phenylethyl)-5,5-dimethyl- 1 ,3-cyclohexandione 4 on the vinyl­triphenylphosphonium cation 3 to form the phos­phorane 5, which is converted into spiroalkene 6.

(CSHS)3rtY=CHC02CH3�6 -. C02CH3 0

"' I 3 ,... \ /-

4

CHCI3 • reflux

6

2

o fHC02CH3 o ?!-C02CH3 P(CsHS)3

5

The structure of compound 6 was deduced from its elemental analysis and its 'H and 13C NMR spectra. The mass spectra of this compound displayed molecu­lar ion peak at mlz 384. Initial fragmentations involve loss from or of the spiroalkene side chains (CH30H, C02CH3).

The IH NMR spectrum of 6 exhibited five single sharp lines, readily recognizable as arising from a gem-dimethyl (8 0.95 and 1 . 12), two methoxy (0 3.60

RAMAZANI et al. : SYNTHESIS OF SUBSTITUTED SPIRO[4.5)DECA-2-ENE- I ,2-DICARBOXYLATE 597

and 3.67) and a methine (8 4.62) protons, along with a fairly complex multiplet for two methylene (6-membered ring), a AB-quartet for a methylene (5-membered ring), and a fairly complex multiplet for a phenyl moieties (see Experimental' Section).The noise-decoupled I3C NMR spectrum of 6 showed twenty distinct resonances in agreement with the asymmetrical structure of 6. Partial assignments of these resonances are given in Experimental Section.

The structural assignments made on the basiS of the IH and I 3C NMR spectra of compound 6 was sup­ported by study of its IR spectrum. Of special interest is the carbonyl absorption at 1 692 cm-I for this com­pound. Conjugation with the carbon-carbon double bond appears to be a plausible factor in the reduction of this band. IS

The one-pot nature of the present procedure makes it an alternative to multistep approaches.2 The proce­dure described here may be extensible for the prepara­tion of spiro[4.5]decane carbon skeleton natural products.2 Further applications of this type of addi­tion-cyclization to the synthesis of interesting carbo­cycles will be reported in due course.

Experimental Section Melting points were measured on an Electrother­

mal 9100 apparatus and are uncorrected. Elemental analyses were performed using a Heraeus CHN-O­Rapid analyzer. IR spectra were recorded on a Shima­dzu IR-460 spectrometer, In and I3C NMR spectra on JEOL EX-90A spectrometer at 90 and 22.6 MHz, re­spectively and mass spectra on a Finnigan-Matt 8430 mass spectrometer operating at an ionization potential of 70 eV.

Preparation of 2-(2-oxo-2-phenylethyl)-S,S-di­methyl-l,3-cyc1ohexanedione 2. Compound 2 was prepared by known methodl6 and identified as follows: white crystals, m.p. 1 80- 1 82°C; IH NMR (CDCh): 8 1 .04 (6H, s, 2CH3); 2.32 (4H, s, 2CH2); 4.03 (2H, s, CH2COPh); 7 .3-7.6 (3H, m, arom.); 8.0-8.2 (2H, m, arom.); pick of OH is not observable (probably, its sig­nal is very broad); I3C NMR (CDCh): 8 28.26 [e3CH3hc]; 30.66 e3CMe2); 3 1 .80 (2 CH2); 53-.-96 ( 13CH2COPh); 106.93 (HOC=13C-C=O); 1213:84 and 129.66 (2 CH of ortho and meta, arom.); 1 34.38 (CH of para, arom.); 135 .54 (C of ipso, arom.); 197.33 (H013C=c-13C=O); 203.24 e3COPh).

Preparation of dimethyl 8,8-dimethyl-6,1O-dioxo-3-phenylspiro[ 4.S]deca-2-ene-l,2-dicarboxy-late 6. To a magnetically stirred solution of triphenyl­phosphine (0.524 g, 2 mmole) and 2-(2-oxo-2-phenyl-

ethyl)-5,5-dimethyl- l ,3-cyclohexandione 2 (0.5 16 g, 2 mmole) in CHCh (7 mL) was added dropwise a mix­ture of dimethyl acetylenedicarboxylate (0.284 g, 2 I

mmole) in CHCh (4 mL) at - 10°C over 10 min. The reaction mixture was then allowed to warm up to room temperature and refluxed for 24 hr. The solvent was removed under reduced pressure and the residue was purified by silica gel (Merck silica gel 60, 230-400 mesh) column chromatography using ethylacetate­hexane ( 1 :5) as eluent. The solvent was removed under reduced pressure and product (0.50 g, light yellow oil, 65%) was obtained; IR (KBr) : 1725 and 1692 (C=O); 124 1 and 1202 cm-f (C-O); IH NMR: (CDC h) 8 0.95 and 1 . 12 (6 H, 2 s, 2 C!h); 2.48-3. 1 8 (4 H, m, 2 CH2); 3.60 and 3.67 (6 H, 2 s, 2 OCH3); 3.69 and 3.79 (2 H, . 2 AB-q, 1HH=6.2 Hz, CH2); 4.62 ( 1 H, s, CH) and 7.2-7.5 (5 H, m, arom.); I3C NMR (CDCI3) : 8 28.06 and 28.67 (2 CH3); 30.54 (C4); 30.87 (C8); 43.86 and 50.78 (C7 and C9); 5 1 .47 and 52.37 (2 OCH3); 57.66 (Cl ); 7 1 . 14 (C5); 123.87 (C2); 127.94 and 129.29 (2 CH of vrtho and meta, arom.); 128.88 (CH of para, arom.); 1 34.75 (C of ipso, arom.); 1 52.83 (C3); 164.5 1 and 170.58 (2 C=O, 2 C02Me); 204.38 and 204.70(2 C=O, C6 and C1O). MS (mlz, %): 384 (M+, 5); 352 (M+- CH30H, 45); 292 (M+- 2 CH30H - CO, 15); 104 (PhCH=CH2+, 1 3). Anal. Calc. for C22H2406 (384.43): C, 68.74; H, 6.29. Found: C, 68.9; H, 6. 1 %.

Acknowledgement This work was supported by the Zanjan University

Research Council.

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