Efficient Synthesis of ortho-Carborane by Reaction of Propiolic Acid tert-Butyl Ester with Decaborane(14)

Abstract

Reaction of propiolic acid tert-butyl ester 1 and decaborane(14) at 90 °C did not give the expected carborane carboxylic acid tert-butyl ester 3 but directly unsubstituted ortho-carborane 2 which was isolated in 52% yield as pure material. An in situ de-tert-butoxycarbonylation of the first formed carborane carboxylic acid tert-butyl ester 3 via a six membered transition state is suggested for this domino process.

alkynes - carboranes - domino reactions - electrocyclic reactions - tert-butyl esters

References

For reviews see:

1a Barth RF. Soloway AH. Fairchild RG. Cancer  1992,  70:  2995 

1b Hawthorne MF. Angew. Chem. Int. Ed. Engl.  1993,  32:  950 ; Angew. Chem. 1993, 105, 997

1c Morin C. Tetrahedron  1994,  50:  12521 

1d Gabel D. Chem. Unserer Zeit  1997,  31:  235 

1e Soloway AH. Tjarks W. Barnum BA. Rong F.-G. Barth RF. Codogni IM. Wilson JG. Chem. Rev.  1998,  98:  1515 

2a Tietze LF. Bothe U. Chem.-Eur. J.  1998,  4:  1179 

2b Tietze LF. Bothe U. Schuberth I. Chem.-Eur. J.  2000,  6:  836 

2c Tietze LF. Bothe U. Griesbach U. Nakaichi M. Hasegawa T. Nakamura H. Yamamoto Y. Bioorg. Med. Chem.  2001,  9:  1747 

2d Tietze LF. Bothe U. Griesbach U. Nakaichi M. Hasegawa T. Nakamura H. Yamamoto Y. ChemBioChem  2001,  2:  326 

2e Tietze LF. Griesbach U. Bothe U. Nakamura H. Yamamoto Y. ChemBioChem  2002,  3:  219 

3a Zakharkin LI. Grebennikov AV. Izv. Akad. Nauk. SSSR, Ser. Khim.  1967,  6:  1376 

3b Gomez FA. Hawthorne MF. J. Org. Chem.  1992,  57:  1384 

3c Nakamura H. Aoyagi K. Yamamoto Y. J. Org. Chem.  1997,  62:  780 

4 Nakamura H. Aoyagi K. Yamamoto Y. J. Am. Chem. Soc.  1998,  120:  1167 

5 Greene TW. Wuts PGM. Protective Groups in Organic Synthesis   Wiley; New York: 1999. 

6 Nemoto H. Rong FG. Yamamoto Y. J. Org. Chem.  1990,  55:  6065 

7 Heying TL. Ager JW. Clark SL. Mangold DJ. Goldstein HL. Hillman M. Polak RJ. Szymanski JW. Inorg. Chem.  1963,  2:  1089 

8 Zakharkin LI. Chapovski YA. Brattsev VA. Stanko VI. Zh. Obshch. Khim.  1966,  36:  878 

9 Wiesboeck RA. Hawthorne MF. J. Am. Chem. Soc.  1964,  86:  1642 

10 Fein MM. Grafstein D. Paustian JE. Bobinski J. Lichstein BM. Mayes N. Schwartz NN. Cohen MS. Inorg. Chem.  1963,  2:  1115 

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Experimental details: Decaborane(14) (1.18 g, 9.65 mmol) was heated in CH₃CN (15 mL) to reflux under exclusion of oxygen and moisture. After 30 min a solution of propiolic acid tert-butyl ester 1 (900 mg, 7.13 mmol) in toluene (15 mL) was added and the resulting mixture heated for 15 h to reflux upon which it turned dark. For work-up, MeOH (1 mL) was added and the mixture refluxed for 30 min, then concentrated in vacuo and filtered through a small plug of silica gel to remove base line impurities with an n-pentane-EtOAc 1:1 mixture as eluent. Purification by column chromatography (n-pentane-EtOAc = 10:1) furnished pure ortho-carborane 3 (533 mg, 52%) as a colorless wax-like solid. R_f (n-pentane-EtOAc = 5:1): 0.69; IR (KBr): 3070
cm^-1 (C-H), 2575 (B-H), 1015, 714; ¹H NMR (200 MHz, CDCl₃): δ = 0.70-3.80 (m_br, 10 H, BH), 3.56 (s_br, 2 H, CH); ¹³C NMR (50 MHz, CDCl₃): δ = 54.36 (2 C, CH); HRMS: calcd for C₂H₁₂B₁₀: 144.1943; found: 144.1943.

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Ortho-carborane was purchased from Acros.

13a Tietze LF. Beifuss U. Angew. Chem., Int. Ed. Engl.  1993,  32:  131 ; Angew. Chem. 1993, 105, 137

13b Tietze LF. Chem. Rev.  1996,  96:  115 

13c Tietze LF. Haunert F. In Stimulating Concepts in Chemistry   Shibasaki M. Stoddart JF. Vögtle F. Wiley-VCH; Weinheim: 2000.