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Influence of Cyclopropyl Substituents on the Relative Rate of Dichlorocarbene Addition to Olefins.

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[6] L. L. Miller, J . F. WoK E. A. Mayeda, J. Am. Chem. Soc. 93, 3306
(1971); E . A . Mayeda, L. L. Miller, J . F . WOK ibid. 94, 6811 (1972);
S . M. Weinreb, G . A . Epling, R. Cumi, M . Reitano, J. Org. Chem. 40,
1356 (1975).
[7] Acetonitrile (Merck), water content 0.5 %.
Influence of Cyclopropyl Substituents on the Relative
Rate of Dichlorocarbene Addition to Olefinsp'l
By Eckehard T.: Dehmlow and Axel Eulenberger[*]
Enormous rate enhancements caused by cyclopropyl rings
adjacent to developing positive charges are well known. However, the influence of cyclopropane on additions to double
bonds is less clear: In hydratation and bromination, cyclopropane accelerates relative to n-butyl by about lo4['], and in
cycloadditions with tetracyanoethylene and arylsulfonyl isocyanates accelerations of lo3 are found[']. Only small differences are observed, however, when arylsulfenyl chlorides are
added'']. In the ene-reaction with singlet oxygen, the electronic
effect of cyclopropane is comparable with that of methyl[31.
We subjected a number of cyclopropylalkenes to reaction
with dichlorocarbene generated by phase-transfer catalysis[4]
and characterized the products. The same olefins were subsequently employed in competition experiments with less than
equivalent amounts of dichlorocarbene. Analysis was performed by gas chromatography after calibration for each of
the products determined in the preliminary experiments. Table
1 shows the reactivities (f5 %) relative to 3,3-dimethyl-lbutene ( 1 4 ) . Steric and electronic effects seem to counteract
.Table 1 . Relative reactivities of various alkenes towards dichlorocarbene.
Alkene
Re].
reactivity
Alkene
each other. A cyclopropyl ring exerts a powerful accelerating
effect compared to its open-chain analog [ ( / 0 ) / ( 1 2),
(1 1 ) / ( I 4), ( 5 ) / ( 1 3 ) ] but-depending on the steric situationthis effect is somewhat more [ ( 2 ) / ( 4 ) ] or somewhat less
pronounced [ ( 3 ) / ( 1 ) , ( 5 ) / ( 4 ) ] than that of methyl. Furthermore, the effect of a double bond is roughly comparable
to that of a three-membered ring. I-Methylcyclopropyl compounds [(6)/(1 I )] are less reactive than the unsubstituted
compounds [(2)/(10)] for steric reasons.
Thus it is apparent that no significant cyclopropyl effects
occur in an unequivocally concerted cycloaddition with little
charge separation in the transition state. Finally, the selectivities of dibromo- and chlorofluorocarbene towards the
cyclopropylalkene pair [ ( 2 ) / ( 5 ) ] were compared. As expected
CClF (relative reactivity R, = 1.82) was more selective than
CClz ( R ,= 1.55),and CBrz (R,= 1.29) was less selective.
Received: June 5, 1978 [Z 23 IE]
German version: Angew. Chem YO. 716 (1978)
CAS Registry numbers.
( I ) , 18738-69-7; ( 2 ) , 4663-22-3; ( 3 ) , 23603-63-6; (4), 115-11-7, (5). 822-93-5;
(6), 78-79-5; (7), 3422-07-9; ( S ) , 110-83-8; ( Y ) , 106-99-0; ( l o ) , 693-86-7;
( J l ) , 16906-27-7; ( J Z ) , 563-45-1; ( J 3 ) , 16746-02-4; ( / 4 ) , 558-37-2;
dichlorcarbene, 1605-72-7
[ I ] D. G . Garratt, A . Modro, K. Oyama, G . H . Schmidt, T T Tidwell, K .
Yates, J. Am. Chem. SOC.96, 5295 (1974).
[2] F. E&berger, 0. Gerlach, Chem. Ber. 107, 278 ( I 974).
[3] A . A . Frimer, D. Rot, M . Spreeher, Tetrahedron Lett. 1977, 1927.
[4] E . V Dehmlow, Angew. Chem. 86, 187 (1974); 8Y, 521 (1977); Angew.
Chem. Int. Ed. Engl. 13, 170 (1974); 16, 493 (1977).
Rel.
reactivity
Dimethylsilanediyliron Complexes[l ]
2035
(8)
200
1415
(9)
140
970
(JO)
100
950
(JJ)
76
910
(12)
12
830
(13)
9
By Hideki Sakurai, Yoshijiasu Kamiyama, and Yasuhiro Nakadaira"]
Schmid et al!'] recently reported the preparation of base-stabilized silanediyliron complexes. We now wish to communicate
our observations on the first stable mononuclear dimethylsilanediyliron complexes.
When a yellow-orange suspension of FeZ(C0)9 (l.OOg,
2.75 mmol) and pentamethyldisilane (I ) (498 mg, 3.77 mmol)
in benzene (10ml) was stirred at room temperature for 1Sh
under argon, a yellow-brown homogeneous solution was
obtained, from which a
yellow-orange
complex
tricarbonylhydrido(dimethylsi1anediyl)trimethylsily~iron( 3 )
(523 mg, 1.92 mmol) was isolated in 70 % yield as an oil, b. p.
30 oC/O.OOS torr.
Fe2(CO),
+
H-SiMez-SiMezR
( I ) , R = Me
(2), R = H
744
(141
1
--+
r
Me,Si=Fe(CO)s
I
SiMezR
+
...
( 3 ) , R = Me
(4), R = H
~
[a] Addition to methyl-substituted double bond
[b] Monoaddition.
[*] Prof. Dr. E. V. Dehmlow, Dipl.-Ing. A. Eulenberger
Institut fur Organische Chemie der Technischen Universitat
Strasse des 17. Juni 135, D-1000 Berlin 12 (Germany)
[**I Support by the Deutsche Forschungsgemeinschaft and the Fonds der
Chemischen Industrie is gratefully acknowledged.
674
The complex ( 3 ) is extremely air-sensitive and decomposes
instantaneously on exposure to air, but correct elemental analyses are obtained on careful handling. The 'H-NMR (CSz)
spectrum of ( 3 ) shows, in addition to the FeH signal at
[*] Prof. Dr. H. Sakurai, Dr. Y . Kamiyama, Dr. Y. Nakadaira
Department of Chemistry, Faculty of Science, Tohoku University
Sendai 980 (Japan)
Angew. Chem. Int. Ed. Engl. 17 ( 1 9 7 8 ) N o . 9
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dichlorocarbene, cyclopropyl, relative, substituents, additional, rate, olefin, influence
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