Organometallics 1986, 5, 603-604
603
synthetic applications of these organometallics reported to date result in mixtures of allenic and propargylic products (eq 1). Our recent discovery of a convenient new
the M-H bond or the "tucked-in" position of the C4Me4 ligand. Evidence in support of this mechanism is that (1) the cyanamide ligand in I1 is easily replaced by py and (2) that Moz(ONp),(p-C4Me4) (py) in the presence of EtzNCN will also form I11 at slightly higher temperatures. Further kinetic studies are in progress in order to gain a better understanding of this unusual reaction.6
RC=CCH2M
-
RC?CCHzX
-
t
M
I
R~=C=CH~
( I )
X
I
S u p p l e m e n t a r y M a t e r i a l Available: Tables of fractional coordinates and isotropic thermal parameters, anisotropic thermal parameters, bond distances, bond angles, and structure factor amplitudes for compounds I and I1 (52 pages). Ordering information is given on any current masthead page.
RC=C=CHz
route to allenic and propargylic organomercurichalides (eq 2 and 3)l appeared to offer possible solutions to both of I
I
(6) We thank the Department of Energy, Office of Basic Sciences,
R C H C E C H f Hg
Chemical Division for support of this work.
RCECCHJ
-
+ Hg
hv
RCH=C=CHHgI
(2)
RCECCHZHgI
(3)
hv
these problems, since these organometallics do not appear to equilibrate and their method of synthesis readily accommodates functionality. At this time we wish to report our preliminary results on the bromination and iodination of these organometallics. Our results to date are summarized in Table I. All halogenation reactions were carried out by using the following general procedure. The halogenating agent (0.5 mmol) dissolved in 5 mL of pyridine was added to a solution of the organomercurial (0.5 mmol) in 5 mL of pyridine at the appropriate temperature. After 5-min reaction time, methylene chloride was added and the organic layer was washed successively with 3 M NazSz03,water, 1 N HC1, and water. After the solution was dried over MgS04, the solvent was removed affording essentially pure organic halide. The purity and ratio of organic halides was established by 'H NMR spectroscopy. The structure of the products was confirmed by IR spectroscopy, high-resolution mass spectrometry, and comparison with literature data. The reaction of both the allenic and propargylic organomercurials with iodine proceeds readily at room temperature to -40 "C in pyridine to afford the corresponding rearranged propargylic or allenic iodides respectively. No more than minor amounts of the products of retention were observed. The use of solvents other than pyridine
Mercury in Organic Chemistry. 32. Bromination and Iodination of Allenic and Propargylic Organomercurials: A Convenient Synthesis of 3-Halo-l,2-aikadienes Richard C. Larock" and Mln-Shine Chow Department of Chemistry, Iowa State University Ames, Iowa 50011 Received November 12, 1985
Summary: The bromination (pyridinium hydrobromide perbromide) and iodination (iodine) of allenic and propargylic organomercuric halides in pyridine proceeds with rearrangement to afford the corresponding propargylic and allenic halides, respectively. This procedure provides a convenient, new route to 3-bromo- and 3-iodo-1,2-alkadienes useful in organic synthesis.
While there has been considerable recent interest in the application of allenic and propargylic organometallics in organic synthesis, two major problems in this area remain. Few of the organometallics so far studied accommodate many important functional groups, and the majority of the
Table I. Halogenation of Allenic and Propargylic Organomercurials
entry
organomercurial CH,
1
\
I
Hi
4 5 6 7 8 9 10
I
< 2/98
I2
-40
CH,CHIC=CH
85
C,H,NHBr,
- 40
CH,CHXC=CH (X: B r / I = 9 3 / 7 )
82
I2
- 40
CH,CHIC-CC,H,
95
I2 C,H,NHBr,
25 - 40
CH,CI=C=CH2 CH,CX=C=CH, (X: Br/I= 92/8) C,H,CI=C=CH, C,H,CX=C=CH, (X: Br/I = 9 9 / 1 ) C,H ,CBr= C= CH, CH, 0 2 C (CH, ),CI=C=CH , CH,O,C(CH,),CX=C=CH, (X: B r / I = 4 4 / 5 6 )
77 71
-1OO/O
100 94
-1oo/o
0/100
C,H,
c=c=c
I
%
yield, product(s)
HgI
2 CH,,
reactn temp, "C
H
c=c=c \
3
halogenating agent
ratio of allenic to propargylic halide
\
H HgI CH,C=CCH,HgI C,H,C=CCH,HgI C, H ,C&CH 2HgBr CH,O,C(CH,),C-CCH,HgI
C,H,NHBr,
25 25
C,H,NHBr, 1, C,H ,NHBr,
25 25 -40
I 2
0276-7333/86/2305-0603$01.50/0
0 1986 American Chemical Society
94 97 82
< 2/98 98/2 92/8
99/1 1oo/o 1oo/o
604 Organometallics, Vol. 5, No. 3, 1986
Communications
generally led to more complicated mixtures of allenic and propargylic iodides. Bromination of these same organomercurials is best effected by using pyridinium hydrobromide perbromide at -40 to 25 "C in pyridine for 5 min. Bromine itself tended to give large amounts of polybrominated products, and mixtures of organic bromides and iodides were obtained when organomercury iodides were employed. The former problem can generally be circumvented by using the pyridinium reagent, but mixtures of organic bromides and iodides are still observed. Organomercuric bromides, however, brominate cleanly with the pyridinium reagent. While a number of ways of preparing allenic halides are known,2 relatively little work has been reported on the halogenation of allenic or propargylic organometallics. Allenylsilver compounds, though of limited availability, have been reported to react with N-chloro- or N-bromosuccinimide, cyanogen bromide and iodine to afford the corresponding l-hal0-1,2-alkadienes.~ Allenic and propargylic tin compounds iodinate with rearrangement to yield propargyl iodides and l-iodo-l,2-alkadienes respect i ~ e l y . ~Finally, propargylic silanes react with bromine
Acknowledgment. We gratefully acknowledge the National Institutes of Health (GM 24254) and the American Heart Association, Iowa Affiliate, for their generous financial support of this research.
(1)Larock, R. C.; Chow, M.-S. Tetrahedron Lett. 1984, 25, 2727. (2) "The Chemistry of the Allenes": Landor. S. R.. Ed.: Academic Press: 1982: Vol. 1. DD 75-93. (3) Westrhijze, H:;'kleijn, H.; Bos, H. J. T.; Vermeer, P. J . Organomet. Chem. 1980, 199, 293. (4) Simo, M.; Sipeuhou, J. A.; Lequan, M. J . Organomet. Chem. 1972, 35, C23.
(5) Flood, T.; Peterson, P. E. J . Org. Chem. 1980, 45, 5006. (6) Corey, E. J.; Kang, J. J . Am. Chem. SOC. 1981, 103, 4618. (7) Corey, E. J.; Kang, J. Tetrahedron Lett. 1982, 23, 1651. (8) Corey, E. J.; Raju, N. Tetrahedron Lett. 1983, 24, 5571. (9) Corey, E. J.; De, B. J . Am. Chem. SOC.1984,106, 2735. (10) Larock, R. C. "Organomercury Compounds in Organic Synthesis"; Springer-Verlag: New York, 1985; Chapter 3.
and iodine to generate 3-halo-1,2-alkadienes, a class of compounds apparently not available by any other route.5 This latter approach has found considerable recent use in eicosanoid s y n t h e ~ i s . ~While -~ the halogenation of organomercurials has been extensively studied,'O there are no previous reports of the halogenation of the virtually unknown allenic and propargylic mercurials. We believe that our propargylic mercurial halogenation procedure provides a useful alternative to the silane approach to 3-halo-1,2alkadienes due to the ready availability of the mercurials and their ability to accommodate considerable functionality. This is illustrated by the ease with which we have been able to prepare intermediates useful in prostaglandin synthesis (see entries 9 and 10 in Table I). We are presently studying other potential applications of allenic and propargylic mercurials in organic synthesis and hope to report on these shortly.
