Cyclization of vinyl and aryl radicals generated by a nickel(II) complex catalysed electroreduction

Tetrahedron Lcncrs. Vol. 35, No. 5. pp. 125-728. 1994 Elsevier Science Ltd printed in Great Britain 00404039B4 56.OfMMO

0040-4039(93)EO275-0

CYCLIZATION OF VINYL AND ARYL RADICALS GENERATED BY A NICKEL(I1) COMPLEX CATALYSED ELECTROREDUCTION Shigeko

Ozaki,

* Ikuo

and Faculty

Hidenobu

of Pharmaceutical

l-6,Yamadaoka,

Abstract:Radical

using

Vinyl and aryl radicals extensively

Suita,

cyclization

electroreduction

reacive towards

Horiguchi,

cyclization

are valuable

Sciences,

Osaka

Osaka-fu,

565 Japan

and

aryl

complex

halides

was

performed

by indirect

as a catalyst.

intermediates

in synthesis

than related alkyl radicals.

on vinyl and aryl radical cyclization 4 viewpoints.

the cyclization

because

they are more

Since Stork and Beckwith

developed

performed by tin hydride method from both the mechanistic

The vinyl radical induced

of eneynes using phosphorus-centered

reactions have recently been utilized radical and selenoboranes.

routes to vinyl radicals besides the use of tin hydrides, extent than those to alkyl radicals various synthetic applications. radicals

6 which

Alternative

5

have been developed

have been conducted

by many methods

to a less and met

in part, to the fact that the generation

method

such

3 for

as the atom transfer

of

or the

ester method 6b would be more difficult than the related alkyl radicals due to the

strength of sp%-X

bonds (X: halogenetc).

We have shown that the electroreductive using nickel(ll)

however,

must be ascribed,

This

by other methods than tin hydride

thiohydroxamate increased

University

chemistry of vinyl radicals 1 and aryl radicals, 2 there have been many useful studies

and synthetic

vinyl

Matsushita,

Ohmori

of vinyl

a nickel(I1)

Hidenori

complexes

as electron-transfer

generation catalysis

of alkyl radicals

from various

halides

alternative

to the tin

is a useful synthetic

hydride method 7a and is particularly useful for intermolecular alkyl radical addition to olefins 7b and intramolecular cyclization of N-allylic and N-propargyl-a-bromoamides. 7C The advantage over tin hydride method could be attributed to the lack of the active hydrogen

atom donor like tin

hydride,

to hydrogen

which

abstraction. proceeds

would Herein

according

electroreductive

elongate

the lifetimes

we describe to Scheme

generation

of the initially

the cyclization 1 to demonstrate

of vinyl and aryl radicals.

Scheme

1 725

of vinyl

formed

radicals

and aryl radicals

the effectiveness

which

of a Ni(ll)

atom

probably

complex

for

726

The reduction

peak potentials

negative than those of alkyl halides The cyclic voltammetric nickel(h) complexes of Ni(tet a)(Cl04)2

investigation

exhibiting

7bindicated

the NI(I)/Ni(lI)

reductive

buffered (NH4Cl04;

peak potential

cathode in an H-shaped catholytes (Si02)

of the nickel

were subjected

catalyst.

a supporting

than that

The electroreductive electrolyte

radical

(EtNC104; 0.1 M), a

(0.2 equiv. based on the halide) and a proton source

2 equiv. based on the halide) complex,

potentiostatically

-1.3 V using a graphite

divided cell under an inert gas.

to give the cyclized

from the

less negative

to transfer an electron to vinyl or aryl halides.

as the electron-transfer

vinyl or aryl halide (1 mmol), Ni(tet a)(Cl04)2

to be more

-2.5 V vs. SCE).

that nickel(l) species, electrogenerated

was performed in DMF (20 ml) containing

to keep the catholyte

(Table 1) were shown

redox couple at the potential

3 [Epc; - -1.35 Vj are ineffective

Thus, we selected Ni(tet a)(ClO4)2 cyclization

of vinyl and aryl halides

(Epc for simple alkyl bromides were around

to the usual extractive

at the

plate electrode

as a

After all the halides were consumed,

work-up

followed

products. g The results of the electrolysis

by column

chromatography

are summarized

in Table 1.

Table 1 Electroreductive Cyclization of Vinyl and Aryl Halides using Ni(tet a)(ClO4)2 as an Electron-transfer Catalyst a Substrates (E=COzMe)

Epcb

-2.83

Ffmol

C

Products

Products

47

2.6 Y

9@

!Ye

1.5

-2.79

2.3

4

47

ti

E 2.0

(%)d

TC

lb

-2.70

Ymld

E

E

81 f

2b

E

2c

32 F

E

3b -*.02g -2.84

86

2.7 E 4b

75

-2.14 5b

-2.70

3.f

tY 68

58

moMe 6b

‘\,M”“’ H

14 6C

a. Electmlysed as described in the text. b. Cathodic peak potential in V vs. SCE. c. Electricity consuned for complete conversion of substrate. d. Isolated yield based on substrate. e. Determined by GC. f. Eledmlysiswith 2 eqv. of PH2Pt-t. g. Ascribed to reduction of the enone group.

the

727

The resuit in Table 1 show that the present method can be a reliable method for generation of vinyl and aryl radicals to give mono- and bicyclic Cyclization

position.

of the intermediary

for 3a which

mode except

bearing

double

group

in 6-endo

which could be brought about by the disproportionation via 5exo

of 2a afforded

C-5 and

exclusively

produced

Electrolysis

on position

nearly l:l, radicals

bond at a prredictable

vinyl and aryl radicals proceeded

has a methyl

mode.

compounds

preferentially underwent

in 5-exo cyclization

a mixture of 2b and 2c in a ratio of between

mode cyclization of the vinyl radicals.

the stable

tertiary

The lack of hydrogen atom

Indeed, the electrolysis of 2a in the presence of 2 used as an active hydrogen atom donor 16 gave 2b in 81% yield as a sole

donor seems to cause thisdisproportionation. equiv. of Ph2PH

The difference

product.

that in the cyclization

in the yields of cyclic products observed

to give more stable tertiary radicals proceeds more smoothly

less stable primary radical. applied

between 1 b and 2b

The present nickel(U) catalysed

radical generation

indicates

than that giving

procedure

can be

not only to alkyl radical but to vinyl or aryl radical as well under ambient temperature

catalytic amount of the nickel reagent whereas organotin benzene

with use of a stoichiometric

provide a convenient References

and

alternative

hydride method usually requires

method should

hydride method.

Notes

1. (a) G. Stork and N. H. Baine, J. Am. Chem. Sot.. 1982, Ramanathan,

Thus, the present

amount of the hydride,

to the organotin

using

reflux in

Tetrahedron

Leti., 1983,

24,187l;

704,232l;

(b) N. M. Marinovic

and H.

(c) G. Stork and N. H. Baine, Tetrahedron

Lett., 1985,26,5927.

2.

(a) A. L. J. Beckwith and W. G. Gara, J. Chem. Sot., Perkin Trans. 7,1975, (b) A. L. J. Beckwith and G. F. Meijis, J. Chem. Sot., Chem. Commun.,

3.

(a) A. L. J. Beckwith and 0. M. O’Shea, Ft. Moor, Jr., Tetrahedron 1987,

4.

Tetrahedron

Lett., 1986,27,4529;

27,4525;

(b) G. Stok and

(c) D. Crich and S. M. Fortt., Tetrahedron

Let?.,

28,2895.

(a) J. Knight, P. J. Parsons, and R. Southgate, H. Hanessian,

P. Beaulieu,

J. Chem. Sot., Chem. Commun., 1986,

and D. Dube, Tetrahedron

P. J. Parsons J. Chem. Sot., Perkin Trans. 7,1987, 5.

Left., 1988

593 and 795;

1981,136.

(a) T. Kataoka, M. Yoshimatsu, 7. 1993,

formation

(c) J. Knight and

and M. Hori, J. C/rem. Sot., Perkin Trans

and N. K. Terette, Tetrahedron Lett., 1993,

1219.

6. The commonly application

N. S. Simpkins,

27,507l;

1237.

Y. Noda, H. Shimazu,

120; (b) J. E. Brumwell,

34,1215and

Lett., 1988,

used methods besides the tin hydride method for conducting

to organic synthesis of Carbon-Carbon

are well documented:

S. Ozaki, H. Matsushita,

1966,

al kyl radicals in

(a) Radicals in Organic Synthesis:

Bonds, 8. Gies, Pergamon

series vol. 5, 1986; (b) D. P. Curran, Synthesis, 7. (a) S. Ozaki, H. Matsushita,

Press, Oxford, Organic Chemistry

417 and 489 and references therein.

and H. Ohmori, J. Chem. Sot., Chem. Commun.,

1992,112O;

and H. Ohmori, J. Chem. Sot., Perkin Trans. I,1 993, 649; (c) S.

Ozaki, H. Matsushita, and H. Ohmori, J. Chem. Sot., ferkin Trans. 7, in the press. 8. Ni(tet a)(ClO4)2: 5,7,7,12,14,14-hexamethyl-l,4,8,11-tetraazacyclotetradecane nickel(ll) perchlorate.

454; (b)

(b)

728

9.

Spectra/ data for selected products: 1 b: 1H NMR (200 MHz, CDCl3) m, CHHCHMe), 3.74(3H, 1.67-l

2.89(1H,

s, MeC02),

.70(2H,

3.72(6H,

l.l0(3H,

d, CHH=CHP),

4.81 (lH,

s, CHH=),

m, CH2CH2CH2),

s, 2 X MeC02),

52.51 (CH3CO2), MHz, CDCt3)

s, CHkk),

2.40-2.65(2H, m, CHHCHCH),

CMe=CH2),

dd, CHHCHCMe),

2.13(lH,

CH2C=CH2),

1.34-1.43(lH,

2.25(1 H, d, CHHCl-lMe), CHHCHMe),

3.71(3H,

m, CHMe),

2.35(1 H, s, C#HC=CH2), s, MeC02),

3.72(3H,

CHH=C), 41.89(CH), (CO2Me), CHMe), ArH);

CH2C=CH2),

5.03(lH,

s, CHH=C),

49.79(CC02Me),

4.07(1H, 6b:

dd, CHHO),

1 H NMR(270

NH), 3.33(1H,

4.86(1H,

t, CHHO),

m, CHMe), 3,67(lH, t, NCHH),

2.88-3.14(2H.

M. C. Helvenston

and C. E. Castro,

J. Am. Chem.

6.75-6.92(2H,

Sm.,

(Received in Japan 6 Augurt 1993; accepted 12 Ocwber 1993)

4b: 1 H NMR(270 COCHaxHeqC,

1.33(3H,

174.89

d, Me), 3.55(1 H. m,

m, ArH),7.05-7.20(2H,

3.08(1 H, t, NCHH),

s, MeO), 6.59(2H,

1992,

4.94(1 H, s,

and 5O.64(-CH2-),

150.49(C=CH2),

ArH) . 10.

2.91(1 H, d,

s, MeC02),

40_83,41,35,

MHz, CDCl3)

3.75(3H,

4..80(lH,

MHz, CDC13),

s, =CH2),;

3.73(3H,

d, MeCH),

m,

s, MeCO2),

1 H NMR(270

108.93(CH2=C).

MHz, CDC13) l.O3(3H,

s, 2 x MeC02),

1.65 (3H, s,

m, CHCHaxHeqC,

MHz, CDCl3)

1 H NMR(200

(CD2Me).

1.89 (2H, m,

3.73(6H,

3.75(3H,

4.72(2H,

3.07(1 H, d, COHaxHeqC),

5b:

171.63

33.86,

m, CH2=CCH2CHMe),

2.62-2.89(6H,,

13C NMR(67.8

31.16,

2.40(1 H, s, CH#C=CH2),

s, MeC02),

52.72(CH3CO2),

208.32(CH2COCH2);

3b:

1.58-1.79(2H,

MHz, CDC13) 2.04(1 H, dd, CHCHaxHeqC), COCH2CH,and

m, CHHCHMe),

s, C(Me)=CH2], 5.02(1 H, s, CHH=C);

4.84[2H,

d, MeCH),

s, CH2C=CH2),

24.17,

MHz, CDCl3),

s, MeC02),

MHz, CDCl3)

d, CHMeMe),

m, CH2C=CH2),

1H NMR(270

3.73(3H,

s, MeC02),

2.68(2H,

110.64(Ci-i2=C),

2.48-2.57(1H.

3.29[1 H, m, CHC(Me)=CH2],

3.73(3H,

MHz, CDCl3)

0.85(3H,

2.89(2H, 2c:

2.552.61(2H

lc: fH NMR(200

m, CH2CH2CH2), 13C(67.8

d, CHMeMe),

4.99(1 H, s, CHH=C);

0.96(3H,

d, CHhC=CH2),

56.73[C(C02Me)2],

0.81(3H,

4.81(1 H, s, CHH=C),

s. CHH=C),

3.05(lH,

s, CH2=C),

and 39.66(CH2),

1.76(1 H, d, CHHCHMe),

4.91 (lH,

2.04-2.15(4H,

4.74(2H,

2b: 1H NMR(200 CHHCHCH),

d, MeCH),

114,849O.

m,

3.1611 H, br, s,

s,ArH),6.71(1H,

s,