Photo-oxygenation of sulfines

PHOTO-OXYGENATION

OF

B. Zwanenburg, A. Wagenaar,

SULFINNS’

and 3. Strating

Department of Organic Chemistry, Zernikelaan,

Groningen,

The University

The Netherlands

(Receivedin c1(14 October 1970; accepted for publication 21 October 1970)

Sulfines' have been subjected to dye-sensitized with the aim to investigate

the acceptance of singlet oxygen by the

Photolysis

with 520 nm light of oxygen enriched

solutions of thiofluorenone-S-oxide high yield on fluorenone.

3

Similarly,

(I) with methylene

compound

(Table I).

reaction to occur.

>CXT=O

chloroform

p,p*~~~o~diphenyl-sulfinej

(VI) were smoothly converted

Uv,

(II), the w

and phenyl-

into the corresponding

carbonyl

Oxygen, light, and sensitizer were all three essential Evidently,

the conversion

system

blue as sensitizer gave a

sulfone sulfine3 III, cis- and trans-phenyl-chlorosulfine' phenylthio-sulfine'

photo-oxygenation

for the

of the CSO system into the carbonyl

group takes place by reaction with singlet oxygen. Although oxygen oxidation addition

7

definitive

mechanism6,

data are lacking concerning

we propose that singlet oxygen

reaction at the CS-bond followed by fragmentation

Indeed, as expected SO2 could be detected'

the singlet

gives a 1.2-cycloto >c=O

and SO*:

in all cases.

Being a good method for the conversion of the CSO function into the carbonyl group, photo-oxygenation of an aryl arylsulfonyl- (or alkylsulfonyl-) sulfine would provide a possible route to the unknown a-oxosulfones. However, sulfines of this type, e.g. VIII5 and Ix9 remained unchanged during photooxygenation. Also trans-phenyl-phenylsulfinyl-sulfine'(X) resisted the reaction with singlet oxygen. Reactions of singlet oxygen with olefins are known to be sensitive6 to steric and electronic factors, therefore we assums that the inertness of VIII-X to photo-oxygenation is due to steric and electron withdrawing effects of the SO2 and so group. Steric effects probably play the most important role during the photo-oxygenation of mesityl-phenylthio-sulfine' (VII) since this sulfine reacts" much slower than phenyl-phenylthio-sulfine (VI) (see Table I). Sulfine XI, which recently has been prepared11 by photooxygenation of 2,5-dimethylthiophene, appeared to be inert (fortuitously) to singlet oxygen.12 Our results show that the synthetic value of the preparation of sulfines by photo-oxygenation of sulfur compounds is rather limited. Desulfurization of sulfines to carbonyl compounds is also possible by direct photolysis of sulfines with Pyrex filtered UV light.13 (>C=S==O +

>c=o

+

S)

The sulfines I-VII indeed show this reaction. However,

direct photodesulfurization of VIII, IX, X, and XI"

aid not succeed. This failure

parallels the reluctance of these sulfines to photo-oxidation.

REFERENCES AND NOTES 1. Part X in the series: Chemistry of Sulfines; part IX: B. Zwsnenburg, L. Thijs, and J. Strating, submitted for publication. 2. For a recent review on sulfines: B. Zwanenburg and J. Strating, Quart. Reports Sulfur Chem. 2, 79 (1970). 3. B. Zwanenburg, L. Thijs, and J. Strating, Rec. Trav. Chim. 89, 577 (1967). 4. J.F. King and T. Durst, Can. J. Chem. $4, 819 (1966). 5. B. Zwanenburg, L. Thijs, and J. Strating, Tetrahedron Letters, 1268, ---- 2871 see also part IX.

iK . P

I.

$0

Sulfine

a

Q0 S 0' 0 S

2.5 h

3.5 h

4 h

3.5 h

4 h

&

95%

Product (yield)

0

0

7”

Table I

94% b)

95% (a)

74%

(P-CH30c6H4)2c=074%

@

0 c6H5c/:c,

0 c6H5cTc1

(&i-So

-.Sulfine

&@-So

&oa

so

2:

I:

E-S

's

ao2CH3

Go

0

rn3q=p3

4 h

ReactionTim

(VII)

Product (yield)

,@-sQ40$

no reaction

Me

4 h

no reaction

(VIII)

3.5 h

1)

(M)

:

no reaction

3

6h

=

(X)

:

no reaction

(tI’anS

ref lla

SUlfine

(XI)

CiS

Photo-oxygenation of sulfinesinCHCl3 solution (0.005-0.02M) at roomtemperature ReactionTim

(I)

(IV)

(III) 4.15 h

P-cH30C6H4)2C=@ (II)

q

//s=o 6H5C\,l

51

6H5c:c1 S PJ)

(VI)

(a): isolatedas benzoamide;(b): isolatedas benzoic acid; (c): recovered44% of

(c)

4686

No.54

6. a)

C.S.

Foote, Accounts Chem.

Res. 1, 104 (1968);

b) D.R. Kearns, J. Amer. Chem. Sot. 2, 7. Cf.photodxygenation

of enamines

6554 (1969).

(ref 6a), diethoxyethylenes

and A.P. Schaap, J. Amer. Chem. Sot. g, (S. Wasur and C.S. Foote, u., additions,

2,

(P.D. Bartlett

3224 (1970) and tetramethoxyethylene

3225 (1970).

Like the quoted cyclo-

the reaction of singlet oxygen with the CSO group is probably non-

concerted. 8. An oxygen containing gas stream was passed through the irridiated then through an aqueous sodium hydroxide titrated iodometrically.

UsuaIly,

solution and

The amount of sulfite was

solution.

25-30% of SO2 was found.

9. See part IX of this series. 10. This reaction is accompanied its geometrical

isomer.

by some isomerisation

Photo-isomerization

of the trans sulfine into

of sulfines on irradiation

in the

presence of sensitizers has also been observed by A.G. Schulz and R.H. Schlessinger, 11.

a)

C.N.

Chem. Conun. 269, =-

1483.

Skold and R.K. Schlessinger,

b) H.H. Wasserman

Tetrahedron

and W. Strehlow, s.,

Letters, UP,

791;

Aa:p, 795.

12. See also ref lla. 13.

Several

&.,

examples

have been reported: J.F. King and T. Durst, J. Amer. Chem.

22, 2676 (1963); J. Strating, L. Thijs, and B. Zwanenburg,

Rec. Trav.

chim., gJ, 631 (1964); B. 'Zwanenburg, L. Thijs, and J. Strating, M., 577 (1967): ldem, Tetrahedron

Letters, y&!, ---

S. Trippett, J. Chem. Sot. (C), --m,

3453 and A. Majid Hamid and

1612; see also ref 2.

Pg,