Silver ion catalysis in the addition of benzyne to cyclooctatetranene

TetrahedronLetters No.22, pp. 1863-1864,1970.

SILVER ION CATALYSIS

IN THE ADDITION

E. Vedejs Chemistry

PergamonPress.

Printed in Great Britain.

OF BENZYNE TO CYCLOOCTATETRANENE

and R. A. Shepherd

Department, University of Wisconsin, Madison, Wisconsin 53706

(Receivedin USA 27 February 1970; receivedin UK for publication13 April 1970) We have previously (I) in cyclooctatetraene was not characterized, remarkably

shown that decomposition

(COT) affords the monoadducts and phenanthrenei.

In the absence of catalyst

cleaned after soaking in cont. HCl-HN03

reaction between

I and

COT produces

II, III, an isomer IV which

We now report that the product

affected by silver ion catalysis.

scrupulosuly

of benzenediazonium-2-carboxylate

little IV was formed.

IV as a major product.

2 H; 3.78 multiplet,

The structure

2 H; 6.07 singlet,

since II predominated

of IV (mp 54.5'-55.5';

is deduced

from the characteristic

absorption

(E < 600) beyond 235 mu in the ultraviolet

in a flow system at 400'. addition of benzyne

Thus, the uncatalyzed

4-phenyl-1,2,4-triazoline-3,5-dione

while

II becomes

hydrogens

conversion

The stereochemistry

to the least hindered

benzyne reaction to COT.4

assigned

the major hydrocarbon

involve a benzyne-Ag+ support this rationale

is analogous

to the addition of of 0.5 mole

to the reaction mixture

causes

and biphenylene,

5

addition of benzyne

complex with enhanced electrophilic

to benzene may

tendencies.

since polar addition of the benzyne-Ag+

1863

to IV follows

On the other hand, addition

product.

that Ag+ catalyzed

to III3

face of.bicyclo[4.2.0]-

in the relative yields of IV, phenanthrene,

Friedman has proposed

to singlets)

Further evidence

spectrum.

from its partial

% (based on I) of silver acetate or silver fluoborate a drastic reduction

NMR 6 CDC13,

NMR spectrum and the absence of significant

for the carbon skeleton of IV is available

octatriene.

and

2 H; 6.23 four lines, 2 H; 7.13 A2B2, 4 H;

at 3.78 6 causes collapse of all other nonaromatic

from the expected

the

our original

Apparently,

decoupling

upon pyrolysis

(apparatus

to remove trace metals)

results were influenced by traces of unknown catalysts, relatively

ratio is

6

Our results

complex to COT may

1864

lead to the homotropylium planned

to investigate

in the intermediate

ion V which is a likely precursor

of II.

Experiments

are

the nature of u and 71 bonding between silver and carbon orbitals

V.

II

IV

III

V Products

From Catalyzed

and Uncatalyzed

Benzyne Reactions

with COT in CHpClp at 35'. Catalyst

GLPC (Carbowax, 170') Determined Hydrocarbon Products

Relative Yields of Volatile

II

III

IV

None

12%

31%

28%

14%

AgBF4

80%

8%

6%

1%

AgOAc

82%

10%

4%

1%

1%

Unknown'

62%

10%

8%

12%

8%

Phenanthrene

Biphenylene 14% trace

References

11 E. Vedejs, Tetrahedron

Letters 1968, 2633.

21 Compound

IV has been synthesized independently by Prof. L. Friedman, published. We thank Prof. Friedman for informing us of his work.

to be

3) The major product of thermolysis of IV is an isomeric hydrocarbon which is also a pyrolysis product of III. This subject will be considered in more detail elsewhere. 4) A. B. Evnin, R. D. Miller

and C. R. Evanega, Tetrahedron

Letters 1968, 5863.

were determined by 5) The yields of the 2:l adduct 9-phenyl-9,10-dihydrophenanthrene preparative TLC. The ratio of the 2:l adduct to II is 26:l for the uncatalyzed reaction, and 1:ll for the reaction catalyzed by silver fluoborate. In our initial studyl, this ratio was 3.5:1. 6) L. Friedman, J. Amer. Chem. sot., “9,

3071 (1967).