Reaction SMILES: [CH3:1][C:2]1([C:12]([OH:14])=[O:13])[C:4]2([CH2:9][CH2:8][CH2:7][C:6]([CH3:11])([CH3:10])[CH2:5]2)[CH2:3]1.[C:15]([O:19][CH2:20][CH3:21])(=[O:18])[CH2:16]O.C1(N=C=NC2CCCCC2)CCCCC1>C(Cl)Cl.CN(C)C1C=CN=CC=1>[CH2:20]([O:19][C:15]([CH2:16][O:13][C:12]([C:2]1([CH3:1])[C:4]2([CH2:9][CH2:8][CH2:7][C:6]([CH3:10])([CH3:11])[CH2:5]2)[CH2:3]1)=[O:14])=[O:18])[CH3:21]
Reactant: CC1(C)CCCC2(C1)CC2(C)C(=O)O
Reactant: CCOC(=O)CO
Agent: C(=NC1CCCCC1)=NC1CCCCC1
Agent: CN(C)c1ccncc1
Solvent: ClCCl
Product: CCOC(=O)COC(=O)C1(C)CC12CCCC(C)(C)C2
Reaction time: 15 h
Yield: 82.1 %

Procedure:
In N2 atmosphere, AgOAc (120 mg, 0.719 mmol) was dissolved in AcOH (125 ml). At reflux, Zn powder (20.2 g, 309 mmol) was added with stirring, and after additional 10 min. stirring at reflux temperature the heating source was removed. The supernatant was decanted, and the residue washed with AcOH (100 ml) and Et2O (5×100 ml). The insoluble material was then suspended in Et2O (250 ml), and a catalytic amount of Ag wool was added under N2. To this suspension was added at room temperature with vigorous stirring ethyl 2-(3,3-dimethylcyclohexylidene)propionate (25.0 g, 119 mmol), prepared according to Example 1. Subsequently, CH2I2 (41.4 g, 155 mmol) was added dropwise with stirring within 10 min at this temperature, and then the reaction mixture was refluxed for 24 h, before addition of further CH2I2 (20.7 g, 77.3 mmol). After another 64 h stirring at reflux temperature, the heating bath was removed; the reaction mixture was allowed to cool to room temperature, and poured into saturated aq. NH4Cl. The organic layer was separated, and the aqueous one extracted twice with Et2O. The combined organic extracts were washed with water, 40% aq. NaHSO4 and brine, dried (MgSO4) and concentrated on the rotary evaporator to give the crude material (26.5 g). This was then dissolved in hexane (200 ml) and Br2 (1.55 ml) was added dropwise with stirring at room temperature within 30 min. After stirring for 2 h at room temperature, the mixture was poured onto crushed ice (500 g). The organic layer was separated, and the aqueous one extracted twice with Et2O. The combined organic extracts were washed with saturated aq. NaHCO3, water and brine. After drying (MgSO4) and evaporation of the solvent on the rotary evaporator, the resulting residue was purified by FC on silica gel (pentane/Et2O, 99:1, Rf=0.55) to provide 1,5,5-trimethylspiro[2.5]octane-1-carboxylic acid ethyl ester (22.3 g, 84%). This 1,5,5-trimethylspiro[2.5]octane-1-carboxylic acid ethyl ester (17.0 g, 75.8 mmol) was dissolved in EtOH/water (1:1, 300 ml), and NaOH (15.2 g, 380 mmol) was added with stirring. After heating to reflux for 5 h, the EtOH was distilled off, and the reaction mixture was diluted with water (500 ml) prior to extraction. The ethereal washings were discarded, the aq. solution acidified with conc. H3PO4 and extracted with Et2O (3×700 ml). The combined organic extracts were dried (MgSO4), and the solvent was evaporated on a rotary evaporator to furnish 1,5,5-trimethylspiro[2.5]octane-1-carboxylic acid (13.9 g, 94%) sufficiently pure for further transformations. At 0° C., this crude 1,5,5-trimethylspiro[2.5]octane-1-carboxylic acid (1.50 g, 7.64 mmol) was dissolved in CH2Cl2 (20 ml) and treated with ethyl glycolate (790 mg, 7.59 mmol). Then, 4-dimethylaminopyridine (0.18 g, 1.48 mmol) was added at 0° C., and after stirring at this temperature for 5 min. a solution of 1,3-dicyclohexylcarbodiimide (1.73 g, 8.38 mmol) in CH2Cl2 (20 ml) was added dropwise. The cooling bath was removed, and stirring was continued at room temperature for 15 h before separating the precipitates by vacuum filtration. The precipitate was washed with CH2Cl2 (50 ml), and the combined filtrates were concentrated on the rotary evaporator. The crude product (3.77 g) was purified by silica-gel FC (pentane/Et2O, 19:1, Rf=0.48) to provide 1,5,5-trimethylspiro[2.5]octane-1-carboxylic acid ethoxycarbonylmethyl ester (1.76 g, 82%) as an odoriferous liquid.