Stereochemistry of the π-route to 2,4-disubstituted adamantanes

Tetrahedron

Letters

No.16,

STEREOCHEMISTRY

pp.I10$1110,

1971. Pergamon Press.

Printed

OF THE II-ROUTE TO 2,4-DISUBSTITUTED

in Great Britain.

ADAMANTANES (1)

Tadashi Sasaki, Shoji Eguchi and Takeshi Toru Institute of Applied Organic Chemistry, Nagoya University, (Received

Recently,

Faculty of Engineering,

Furo-cho, Chikusa-ku, Nagoya, 464, Japan 1971; receivedin UK for publication19 March 1971)

in Japan 9 February

the n-route

to 2-substituted

(2) and 2,4-disubstituted

(3-S) has drawn much attention because of its synthetic utility. chotomy in the stereochemistry 2,4-disubstituted this communication

adamantanes

of a 4-substituent

route to 2,4-disubstituted

of adamantanone

reaction

on the stereochemistry

Ia under the milder conditions yielded also an equilibrium

(3).

mixture

a mixture

of

(IIa) was obtained instead of pure

Heating of pure Ia in methanesulfonic

acid

of Ia and IIa, indicating a facile equilibri-

the isomers under the reaction conditions.

study reported by McKervey

of the s-

was carried out in methanesulfonic

time and a higher temperature,

4e- (Ia) and 4a-methylsulfonoxyadamantan-2-one

ation between

We wish to report in

adamantanes.

When the Schmidt reaction acid by using a prolonged

interpretation

However, a di-

introduced by the n-route to

remains seemingly unsolved.

a reasonable

adamantanes

et al. (5) revealed

Reinvestigation

of the

that treatment of 4-oxohomoadaman-

tan-s-one with 50% sulfuric acid afforded

a 1:6 mixture of 4e- (Ib) and 4a-hydro-

xyadamantan-2-one

Furthermore,

a mixture

(IIb) in 71.5% yield.

pure II\,was converted

to

of Ib and IIb on treatment with 50% sulfuric acid.

The cyclization

process

could now be interpreted under the stereoelectronic

of the n-route to 2,4-disubstituted

as depicted

an acylium cation cyclizes

control to afford initially a le-isomer which is un-

stable under the acidic conditions 4e- and 4a-isomers via a cationic The equilibrium

in Scheme:

adamantanes

constants

and is converted intermediate

to an equilibrium mixture of

III.

for Ia + IIa were measured 1109

by the nmr analysis,

1110

Ia: X=OMs, Y=O

III

IIa: X=OMs, Y=O

Ib: X=OH, Y=O

IIb: X=OH, Y=O Scheme

from which the thermodynamic Obviously,

parameters

IIa is thermodynamically

ed by the difference group between

were calculated

as summarized

more stable than Ia.

of 1,3-ax-ax nonbonded

interaction

Ia and IIa; in Ia, two such interactions

in Table.

This could be explainrelated to the mesylate

exist between

4e-OMs and

6a-H, and 4e-OMs and lCJa-H, while in IIa, only one between 4a-OMs and 9a-H. obtained

-AG value is somewhat larger than an half of A value reported

substituted

cyclohexanes

The

for mono-

(6), which might be due to some ring deformation

in Ia

and IIa (cf. the nmr data in ref. 3). Table Temp.('C)

K(IIa/Ia)

-AG (Kcal/mol)

76.5

5.83

1.23

65.5

6.01

1.21

47.5

6.24

1.17

25.0

1.13 (extrapolated value)

AH (Kcal/mol)

AS (e.u.)

0.54

-1.97

References (1) Synthesis

of Adamantane

and T. Toru, submitted

Derivatives.

XVI:

Part XV:

T. Sasaki, S. Eguchi

to J. Org. Chem.

(2) D. J. Raber, G. J. Kane and P. v. Schleyer, Tetrahedron (3) T. Sasaki, S. Eguchi and T. Toru, J. Org. Chem., g, (4) C. Udding, H. Wynberg (5) M. A. McKervey,

and J. Strating, Tetrahedron

D. Faulkner and H. Hamill,

(6) F. Jensen, C. Bushweller

Lett., 4117 (1970).

4109 (1970). Lett., 5719 (1970).

ibid., 1971 (1970).

and B. Beck, J. Amer. Chem. Sot., 91, 344 (1969). =