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Borate Complexes Derived from Lithium Carbenoids Ч Mechanism of the УInverse Stevens RearrangementФ.

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Borate Complexes Derived from Lithium
Carbencids - Mechanism of the “Inverse Stevens
Rearrangement” [11
By G . Kobrich and H . R . Merkle[*I
Juger and Hesse 121 have contrasted the nitrogen ylides and
their ability to undergo the cationotropic Stevens rearrangement, with the boron ylides (3) because several anionotropic rearrangements of boron ate-complexes can he ascribed
to the fact that the arrangement of their charges is the reverse
of that in ( I ) . It has been an open question whether this
“inverse Stevens rearrangement” is really to be ascribed to a
boron ylide intermediate stage.
lated o n (12)l on rearrangement and acid hydrolysis. The
cis-isomer of compound (12) gives 98 % p u e trans-oc-methylstilbene (yield 71 %). These findings exclude a boron ylide
intermediate common to the two isomers. The steps (12) +
(13) + (14) and (16) + (17) are electrophilic reactions at
the unsaturated carbon atom with retention of configuration.
It then follows that the rearrangement step (14) + (16) occurs with inversion by rear attack (15) of the phenyl group
o n the carbon atom carrying the chlorine substituent.
(12ja R = H
(13); R = Li
(14), R = %(C6Hs)s Li@
(15)
1
‘GH5,
?CsH5
c =c,
H3C‘
R
( I 6 ) , R = B(C6Hs)z
(17), R = H
Received: November 4th, 1966
[ Z 368 IE]
German version: Angew. Chem. 79, 50 (1967)
We observed inverse Stevens rearrangements when we treated
stable lithium carbenoids (5) [31 with triphenylboron. ateComplexes (6) were slowly formed which rearranged to boranes (7) with elimination of lithium chloride when the mixture was warmed to room temperature or boiled in tetrahydrofuran.
(5)
(aj, R = H
(b). R = C1
(c), R = CH3
Use of dichloromethyl-lithium (8) gives the corresponding
(chlorobenzy1)diphenylborane(9) The ate-complex (10) formed from trans-dichlorovinyl-lithium decomposes at -100 “C
into pure cis-styryl chloride and phenylacetylene (molar ratio
about 1: 3); presumably the borane (11) is first formed.
[*I Doz. Dr. G. Kobrich and Dip1.-Chem. H. R. Merkle
Organisch-ChernischesInstitut der Universitat
TiergartenstraBe
69 Heidelberg (Germany)
[l] Part XXII of Stable Carbenoids. - Part XXI: G. Kobrich,
H. Heinemann, and W. Ziindorf; Tetrahedron, in press. - We
thank the Deutsche Forschungsgemeinschaft, the Wirtschaftsministerium of Baden-Wiirtternberg, and the Fonds der Chemischen Industrie for financial support.
[2] H. Juger and G. Hesse, Chem. Ber. 95, 345 (1962).
[3] For a review, see G. Kobrich et al., Angew. Chern. 79, I5
(1967); Angew. Chern. internat. Edit. 6,41 (1967). Cf. G.Kobrich
and W. Drischel, Tetrahedron, 22, 2621 (1966).
[4] K. Flory, unpublished experiments (1963) ; F. Ansari, Dissertation, Universitat Heidelberg 1966.
t
Ethyl Diazoiodoacetate and its Decomposition to
Ethoxycarbonyliodocarbene
By F. Gerhart, U. Schollkopf, and H . Schumacher[*I
Halogenodiazomethanes are of interest as precursors of
halogenocarbenes and as preparative reagents 111. We obtained ethyl diazoiodoacetate (2),the first characterized halogenodiazoalkane[zl, in about 80% yield when we treated diethyl mercuribisdiazoacetate ( I ) 131 in ether with rather less
than 2 equivalents of iodine. The filtrate was concentrated
(water-pump, room temperature, rotary evaporator) and the
residue was digested with petroleum ether (b.p. 4OoC) to
remove the last traces of mercuric iodide. Compound (2) is a
red oil, stable for days at 0-5 OC, giving IR bands at 2080 and
1680 cm-1. Triphenylphosphazine derivative: m.p. 109 to
112 O C (decomp. ; precipitated from benzene by petroleum
ether).
The ate-complex (14) formed from trans-methylstyryl
chloride (12) v i a the trans-carbenoid compound ( I S ) 141 affords 99% pure cis-a-methylstilbene (17) [yield 65 %, calcu-
74
Angew. Chem. internat. Edit.
I
Yol. 6 (1967) No. I
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уinverse, rearrangements, mechanism, borate, carbenoids, complexes, derived, stevens, lithium
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