[66478-63-5]  · C10H18O2  · Di-t-butoxyacetylene  · (MW 170.25)

(a synthon for oxocarbons,1 it transfers a protected enediol fragment by cycloaddition)

Physical Data: mp 8.5 °C; bp 30 °C/0.05 mmHg; n25D = 1.4365.

Solubility: completely sol hydrocarbons, ethers, chlorinated solvents, and ethyl acetate; insol water.

Form Supplied in: pale yellow oil; not commercially available.

Analysis of Reagent Purity: IR (CCl4) cm-1: 2972, 2922, 1470, 1450, 1390, 1367, 1301, 1263, 1245, 1150, 825; 1H NMR (CCl4) d: 1.31 (s, CH3).

Preparative Methods: from 1,2-dichloro-1,2-dimethoxyethane2 or from trans-2,3-dichloro-1,4-dioxane.2b,3 This latter procedure has been thoroughly optimized4 and involves six steps, beginning with dioxane.

Purification: usual impurities can be removed by column chromatography on neutral alumina using a column refrigerated at 0 °C and eluting with pentane under N2 pressure.

Handling, Storage, and Precautions: most conveniently stored as a solid at -20 °C. It slowly decomposes at rt through elimination of 2-methylpropene.5

Cycloadditions and Cyclooligomerizations of Di-t-butoxyacetylene.

Different carbenes equivalent to CO add to di-t-butoxyacetylene (1) to afford di-t-butoxycyclopropenone (2) (eq 1).1,6 This compound has been quantitatively converted to deltic acid (dihydroxycyclopropenone) by treatment with Trifluoroacetic Acid (TFA).

Simple heating under reflux of a benzene solution of (1) leads to the quantitative formation of 2,3,4-tri-t-butoxycyclobutenone (3) via a [2 + 2] cycloaddition with thermally generated t-butoxyketene (eq 2).6 Compound (3) has been converted to 3-hydroxycyclobutene-1,2-dione (semisquaric acid) by trifluoroacetolysis,7 and to 3,4-dihydroxycyclobutene-1,2-dione (squaric acid) by an oxidation-trifluoroacetolysis sequence.6 The cyclodimerization of (1) can be also induced by PdII. Di-t-butyl squarate is obtained and converted without isolation to squaric acid by treatment with TFA (eq 3).7

Both Dicarbonyl(cyclopentadienyl)cobalt(I) and Nonacarbonyldiiron efficiently induce cyclopentadienone formation from (1) (eq 4).7,8 Demetalation of complex (4) leading to tetra-t-butoxycyclopentadienone has been achieved electrochemically,9 whereas complex (5) is most conveniently demetalated with Trimethylamine N-Oxide.8 Tetra-t-butoxycyclopentadienone has been converted to 2,4,5-trihydroxycyclopent-4-ene-1,3-dione (hydrocroconic acid) and to 4,5-dihydroxycyclopent-4-ene-1,2,3-trione (croconic acid).8,9

Catalytic amounts of Octacarbonyldicobalt6 or, better, Tetracarbonylnickel,1,10 induce cyclotrimerization of (1) leading to hexa-t-butoxybenzene (6) under unusually mild conditions (eq 5). Trifluoroacetolysis of (6) affords quantitatively hexahydroxybenzene, the classical precursor of 5,6-dihydroxycyclohex-5-ene-1,2,3,4-tetrone (rhodizonic acid).

1. Serratosa, F. ACR 1983, 16, 170.
2. (a) Pericàs, M. A.; Serratosa, F. TL 1977, 4433. (b) Bou, A.; Pericàs, M. A.; Serratosa, F. T 1981, 37, 1441.
3. Pericàs, M. A.; Serratosa, F. TL 1978, 2603.
4. Bou, A.; Pericàs, M. A.; Riera, A.; Serratosa, F. OS 1987, 65, 68; OSC 1993, 8, 161.
5. (a) Brandsma, L.; Bos, H. J. T.; Arens, J. F. In Chemistry of Acetylenes; Viehe, H. G., Ed.; Dekker: New York, 1969; pp 808-810. (b) Moyano, A.; Pericàs, M. A.; Serratosa, F.; Valentí, E. JOC 1987, 52, 5532.
6. Pericàs, M. A.; Serratosa, F. TL 1977, 4437.
7. Bou, A.; Pericàs, M. A.; Serratosa, F. TL 1982, 23, 361.
8. Fornals, D.; Pericàs, M. A.; Serratosa, F.; Vinaixa, J.; Font-Altaba, M.; Solans, X. JCS(P1) 1987, 2749.
9. Bou, A.; Pericàs, M. A.; Serratosa, F.; Claret, J.; Feliu, J. M.; Muller, C, CC 1982, 1305.
10. Camps, F.; Coll, J. J.; Moretó, J. M.; Torras, J. JOC 1989, 54, 1969.

Miquel A. Pericàs

Universitat de Barcelona, Spain

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