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Synlett 2009(7): 1180-1184  
DOI: 10.1055/s-0028-1088120
LETTER
© Georg Thieme Verlag Stuttgart ˙ New York

Di-µ-Hydroxy-bis(N,N,N′,N′-tetramethylenediamine)copper(II) Chloride {[Cu(OH)˙TMEDA]2Cl2} Catalyzed Tandem Phosphorous-Carbon Bond Formation-Oxyfunctionalization: Efficient Synthesis of Phenacyl Tertiary
Phosphine-Boranes

Gullapalli Kumaraswamy*a, Gadde Venkata Raoa, Akula Narayana Murthya, Balasubramanian Sridharb
a Organic Division III, Indian Institute of Chemical Technology, Hyderabad 500 007, India
Fax: +91(40)27193275; e-Mail: gkswamy_iict@yahoo.co.in;
b Laboratory of X-ray Crystallography, Indian Institute of Chemical Technology, Hyderabad 500 007, India
Further Information

Publication History

Received 2 January 2009
Publication Date:
26 March 2009 (online)

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Abstract

A novel [Cu(OH)˙TMEDA]2Cl2 catalyzed tandem reaction has been developed for the synthesis of a series of sterically and electronically divergent phenacyl tertiary phosphine-boranes.

Key words

phosphine-boranes - terminal alkynes - phenacyl tertiary phosphine-borane - copper iodide - methyl propiolate

    Reference and Notes

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8

Other copper salts evaluated for this transformation are CuOTf, CuOAc, CuCl, CuCl2, Cu(Piv)2, [Cu(MeCN)4]PF6, and Cu(acac)2. Except CuCl2 (30%), none gave target compound.

9

Various solvents and bases were screened for the optimization of yield of 3b. Halogenated solvents (CH2Cl2, CHCl3, DCE) and toluene failed to give the product. In addition to MeCN, only the aprotic solvent DMF was successful albeit in low yield (40%). Bases such as K2CO3, Na2CO3, NaHCO3, K3PO4, and KOt-Bu did not yield the observed product.

10

We have performed the reaction under aerobic conditions and under inert atmosphere. In both cases the product formation was observed but in open air a slightly better yield was obtained. Further, using an oxygen balloon, the reaction did not proceed. These experiments imply that the dissolved air is essential for the product formation. At present, we have no satisfactory explanation for this phenomenon and it clearly needs further work.

11

Typical Procedure
Secondary phosphine-borane (±)-1b (198 mg, 1.1 mmol) and phenyl acetylene (2a, 198 mg, 1.0 mmol) were dissolved in MeCN (5 mL). To this reaction mixture, [Cu(OH)˙TMEDA]2Cl2 (38 mg, 10 mol%) and Et3N (20 mg, 20 mol%) were added sequentially. The resulting reaction mixture was stirred 6 h at ambient temperature. The reaction mixture was quenched with sat. NH4Cl solution and extracted with EtOAc (2 × 10 mL) and washed with brine solution. The combined extracts were dried over anhyd Na2SO4 and filtered, and evaporation under reduced pressure resulted in a crude residue. The residue was subjected to SiO2 column chromatography, and it furnished the phenacyl tertiary phosphine-borane 3b in 80% yield (262 mg).
¹H NMR (300 MHz, CDCl3): δ = 1.18 (d, J = 14.3 Hz, 9 H), 3.55-3.85 (m, 2 H), 7.36-7.53 (m, 6 H), 7.76-7.89 (m, 4 H).¹³C NMR (75 MHz, CDCl3): δ = 25.4, 29.8, 30.1, 128.1, 128.2, 129.0, 131.3, 131.4, 133.4, 133.5, 133.6, 195.9. IR (KBr): 2925, 2855, 2386, 1668, 1143, 1068, 996, 738 cm-¹. MS-FAB: m/z = 297 [M - 1]+. HRMS (ESI-MS): m/z calcd for C18H24PBONa: 321.1415; found: 321.1415.

12

The crystal belongs to the monoclinic crystal system, space group is Cc with a = 11.6520 (7) Å, b = 22.6559 (14) Å, c = 7.5701 (5) Å, β = 117.933 (1), V = 1765.58 (19) ų, ρ calc = 1.122 mg m-³, λ = 0.71073Å, µ(Mo Kα) = 0.152
mm-¹, F 000 = 640, T = 294 (2) K. Data collection yielded 8337 reflection resulting in 3095 unique, averaged reflection, 3041 with I > 2σ(I), θ range: 1.80-25.00˚. Full-matrix least-squares refinement led to a final R = 0.0293, wR = 0.0770 and GOF = 1.013. Intensity data were measured on Bruker Smart Apex with CCD area detector. CCDC 714891 contains the supplementary crystallographic data for the structure 3b. These data can be obtained free of charge from The Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_request/cif.

13

Transformation of styrene 2i into a phenacyl tertiary phosphine-borane 3b can be tentatively rationalized on the basis of Wacker-type oxidation.