Manganese(III)-mediated phosphinoyl radical reactions for stereoselective synthesis of phosphinoylated tetrahydronaphthalenes

Article abstract of DOI:10.1039/c1cc12343b

Reactions of diphenylphosphinoyl radicals with 5-aryl-2-pentenoates or β-phenylethylene styrenes generate trans-substituted tetrahydronaphthalenes through a cascade reaction sequence.

Full text of DOI:10.1039/c1cc12343b

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COMMUNICATION
Manganese(III)-mediated phosphinoyl radical reactions for stereoselective
synthesis of phosphinoylated tetrahydronaphthalenesw
Xiang-Qiang Pan,a Lu Wang,a Jian-Ping Zou*a and Wei Zhang*b
Received 21st April 2011, Accepted 12th May 2011
DOI: 10.1039/c1cc12343b
Reactions of diphenylphosphinoyl radicals with 5-aryl-2-
pentenoates or b-phenylethylene styrenes generate trans-substituted
tetrahydronaphthalenes through a cascade reaction sequence.
Scheme 1
Reaction of phosphorous-centred radicals with unsaturated
compounds to generate phosphorous–carbon bonds is a subject
of current interest.1 Hydrogen transfer of compounds containing
a labile P–H bond is an efficient way to form phosphonyl
radicals [(RO)2P(O)ꢀ] and phosphinoyl radicals [R2P(O)ꢀ].
These radicals add to alkenes at the rates of around
106–107 MÀ1 sÀ1, which are 1 to 2 orders faster than the addition
of carbon-centred radicals.2,3 The greater s-contribution and
pyramidalization of the phosphorous atom makes phosphonyl
radicals more reactive than phosphinoyl radicals.4
A significant amount of effort has been spent on the study of
physical and chemical properties of phosphonyl and phosphinoyl
radicals.5–9 However, the synthetic application of phosphinoyl
radicals is far behind the phosphonyl radicals.1a A literature
search indicated that only the Taillades10 and Parsons11
groups have reported the addition of diphenylphosphinoyl
radicals to alkenes for the synthesis of alkylphosphine oxides.
In those two cases, Et3B and AIBN were used to promote the
formation of phosphinoyl radicals, respectively. Introduced in
this communication is Mn(OAc)3-promoted formation of a
diphenylphosphinoyl radical and its application for cascade
addition and cyclization reactions.
Scheme 2
regioisomers, E/Z isomers, and polymers. When diphenyl-
phosphine oxide 7 was used to replace dimethyl phosphonate 2,
reactions of 5a and 5b both gave complicated mixtures.
However, the reaction of 4a gave a major product 8a. Under
the optimization conditions of using 1 equiv. of 4a, 2 equiv.
of 7, and 2 equiv. of Mn(OAc)3 in acetic acid at 50 1C for
30 min, 8a was prepared in 60% isolated yield (Scheme 2).
By-products generated by hydrophosphinoylation and direct
phosphinoylation on the acrylate and on the phenyl ring were
not observed. X-Ray crystal structure analysis confirmed the
structure of 8a to be a trans-disubstituted tetrahydronaphthalene
(Fig. 1).15 In this reaction, the less reactive phosphinoyl radical
and the ethylene group in 4a provide a right combination to
control the reactivity and selectivity in the formation of
phosphinoylated tetrahydronaphthalene 8a. Similar substrates
6a–c bearing electron-withdrawing groups such as COPh,
CN, and NO2 gave complicated mixtures. It is known that
phosphinoyl radicals are moderately nucleophilic.1a Addition of
a phosphinoyl radical to electron-poor alkenes could be too fast
to give selective products.
We recently reported the Mn(OAc)3-mediated reactions of
phosphonyl radicals for direct phosphonylation of arenes,12
heteroarenes,13 and arylalkenes.14 A reaction of methyl cinnamate 1
with dimethyl phosphonate 2 to form trans phosphonylated
product (E)-3 is shown in Scheme 1.14 To study the role of
the phenyl group in this regio- and stereoselective reaction,
acrylates containing non-conjugated phenyl such as 4a, 5a and
5b were reacted with dimethyl phosphonate 2 in acetic acid at
50 1C. All reactions afforded complicated mixtures containing
a College of Chemistry and Chemical Engineering, Suzhou University,
199 Renai Street, Suzhou, Jiangsu 215123, China.
E-mail: jpzou@suda.edu.cn
b Department of Chemistry, University of Massachusetts Boston,
100 Morrissey Boulevard, Boston, MA 02125, USA.
E-mail: wei2.zhang@umb.edu
A mechanism for the reaction of 5-aryl-2-pentenoate 4a is
proposed in Scheme 3. Phosphinoyl radical 9 adds to the
b-position of the acrylate to form radical 10. This carbon-centered
w Electronic supplementary information (ESI) available. CCDC
816923. For ESI and crystallographic data in CIF or other electronic
format see DOI: 10.1039/c1cc12343b
c
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Chem. Commun., 2011, 47, 7875–7877 7875

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Table 1 Reactions of b-phenylethylene acrylates
Entry
Pentenoate 4
Product 8 and yield
1
2
3
4
Fig. 1 X-Ray crystal structure of 8a.
5
6
7
8
Scheme 3
radical cyclizes to the phenyl ring to yield trans-substituted 11.
It is oxidized with Mn(OAc)3 to give carbocation 12 followed
by deprotonation to afford product 8a.
Reactions of a series of 5-aryl-2-pentenoates 4 indicated that
a methyl at 2-, 4- and 5-positions of acrylate had no significant
effect on the reactivity and afforded trans products in 50–62%
yields (Table 1, entries 2, 4, and 5). X-Ray crystal structure
analysis confirmed the structure of 8d (see ESIw). If the methyl
is at the 3-position, no reaction is observed because of the
steric hindrance at the reaction site (Table 1, entry 3). The
effect of the substituent on the phenyl was also investigated.
It was found that both electron-donating and electron-
withdrawing groups are tolerated (Table 1, entries 6–8).
In a recent paper we reported that the reactions of dimethyl
phosphonate 2 with 1-phenylalkenes 13a–c afforded mixtures
of regio- and E/Z isomers of alkenylphosphonates.14 We
wondered if b-phenylethylene styrene 14a could react with
diphenylphosphine oxide 7 to afford phosphinoylated tetra-
hydronaphthalene product 15a. Indeed, reaction of 1 equiv. of
14a, 2 equiv. of 7, and 2 equiv. of Mn(OAc)3 in acetic acid at
50 1C for 30 min afforded 15a in 55% yield together with
by-product 16a in 21% yield (Scheme 4). A mechanism for the
formation of 15a and 16a is proposed. Radical 17 undergoes
cyclization by following the pathway presented in Scheme 3 to
form desired product 15a. Radical 17 could also be oxidized to
form 18 and then acetylated to yield by-product 16a.
Scheme 4
(Table 2, entries 1 and 2). It is concluded that E/Z isomers of 14a
have no significant impact on product yield and stereochemistry.
Reactions of a series of b-phenylethylene styrenes with
diphenylphosphine oxide 7 are shown in Table 2. The results
indicate that electron-donating and withdrawing groups on the
phenyl ring of styrene are tolerated (Table 2, entries 3 and 4).
The methyl groups at 1-, 2-, 3- and 4-positions of the styrene
were also studied. Except the methyl at the 2-position (Table 2,
entry 6), all other methyl-substituted substrates afforded the
expected phosphinoylated tetrahydronaphthalenes 15 as a
major product together with a small amount of noncyclized
byproducts 16 (Table 2, entries 5, 7, and 8). The reaction of 14h
afforded a complicated mixture (Table 2, entry 9).
Styrene 14a prepared by the Wittig reaction was a mixture
of 7 : 3 E/Z isomers. To understand if isomers could have
different outcomes, (Z)-b-phenylethylene styrene (Z)-14a
was synthesized by hydrogenation of 1,4-diphenyl-1-butyne
with the Lindlar catalyst. Reaction of (Z)-14a with a
phosphinoyl radical gave a very similar result as that for 14a
In summary, we have developed a Mn(OAc)3-mediated
regio- and stereoselective reaction for the preparation of
c
7876 Chem. Commun., 2011, 47, 7875–7877
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Table 2 Reactions of b-phenylethylene styrenes
2-phosphinoylated tetrahydronaphthalenes. 5-Aryl-2-pen-
tenoates and 5-phenylethylene styrenes are good substrates
to form phosphinoylated tetrahydronaphthalenes through a
phosphinoyl radical addition and cyclization process. This
straightforward reaction represents a new application of
phosphinoyl radicals in stereoselective synthesis.
Entry Styrene 14
Products 15 and 16
1
JPZ thanks the National Natural Science Foundation of
China for financial support (No. 20772088).
2
3
4
Notes and references
1 Reviews on P-centered radicals: (a) D. Leca, L. Fensterbank,
E. Lacote and M. Malacria, Chem. Soc. Rev., 2005, 34, 858;
(b) S. Marque and P. Tordo, Top. Curr. Chem., 2005, 250, 43.
2 T. Sumiyoshi, W. Schnabel, A. Henne and P. Lechtken, Polymer,
1985, 26, 141.
3 T. Sumiyoshi and W. Schnabel, Makromol. Chem., 1985, 186, 1811.
4 A. Kajiwara, Y. Konishi, Y. Morishima, W. Schnabel, K. Kuwata
and M. Kamachi, Macromolecules, 1993, 26, 1656.
5 M. Geoffroy and E. A. C. Lucken, Mol. Phys., 1971, 22, 257.
6 C. M. L. Kerr, K. Webster and F. Williams, J. Phys. Chem., 1975,
79, 2650.
7 T. Sumiyoshi and W. Schnabel, Makromol. Chem., 1985, 186,
1811.
8 G. W. Sluggett, P. F. McGarry, I. V. Koptyug and N. J. Turro,
J. Am. Chem. Soc., 1996, 118, 7367.
9 S. Jockusch and N. J. Turro, J. Am. Chem. Soc., 1998, 120, 11773.
10 P. Rey, J. Taillades, J. C. Rossi and G. Gros, Tetrahedron Lett.,
2003, 44, 6169.
11 (a) C. M. Jessop, A. F. Parsons, A. Routledge and D. Irvine,
Tetrahedron Lett., 2003, 44, 479; see also: (b) M. P. Healy,
A. F. Parsons and J. G. T. Rawlinson, Synlett, 2008, 329;
(c) C. M. Jessop, A. F. Parsons, A. Routledge and D. J. Irvine,
Eur. J. Org. Chem., 2006, 1547; (d) J. M. Barks, B. C. Gilbert,
A. F. Parsons and B. Upeandran, Tetrahedron Lett., 2001, 42,
3137.
5
6
7
No reaction
12 W. Xu, J.-P. Zou and W. Zhang, Tetrahedron Lett., 2010, 51, 2639.
13 (a) X. J. Mu, J. P. Zou, Q. F. Qian and W. Zhang, Org. Lett., 2006,
8, 5291; see also: (b) T. Kagayama, A. Nakano, S. Sakaguchi and
Y. Ishii, Org. Lett., 2006, 8, 407.
14 X.-Q. Pan, J.-P. Zou, G.-L. Zhang and W. Zhang, Chem. Commun.,
2010, 46, 1721.
8
9
15 Crystal data for trans-2-diphenylphosphinoyl-1,2,3,4-tetrahydro-
naphthalene-1-carboxylic acid methyl ester C24H25O4P, M =
408.41, triclinic, a = 8.735(3) A, b = 11.975(4) A, c = 12.478(5) A,
a = 61.480(5)1, b = 69.536(3)1, g = 80.201(7)1, U = 1074.5(6) A3,
T = 223(2) K, space group P1, Z = 2, Dc = 1.262 g cmÀ3, Nonius
ꢀ
Kappa CCD diffractometer, m(Mo-Ka) = 0.155 mmÀ1, 9895 indepen-
dent reflections (4850 observed), 270 parameters, Rint = 0.0379,
R = 0.0465, wR(F2) = 0.0866, thermal ellipsoids probability level is
25%. CCDC 816923.
Complicated mixture
c
This journal is The Royal Society of Chemistry 2011
Chem. Commun., 2011, 47, 7875–7877 7877