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Unusual Regioselectivity in the Reaction of Allyl- or Allenylpropargyltitanium Compounds with Carbonyl Compounds An Efficient Synthesis of Alkylidenecyclopropane Derivatives.

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Unusual Regioselectivity in the Reaction of
Allyl- or Allenylpropargyltitanium Compounds
with Carbonyl Compounds:
An Efficient Synthesis of
Alkylidenecyclopropane Derivatives
&,owoEt
6
Aleksandr Kasatkin and Fumie Sato*
Ti(0i Prj2
Recently, we have developed a highly efficient and practical
procedure for preparation of allyltitanium compounds by the
reaction of allylic substrates, including carbonates, with [ ($propene)Ti(OiPr),] (l), which is readily generated from [Ti(OiPr),] and two equivalents of iPrMgBr.‘’’ Allyltitanium compounds, prepared in this way or by transmetalation using
organolithium or -magnesium compounds,[21react with aldehydes exclusively at the most substituted allylic carbon to afford
the “branched” addition product 2 (Scheme 1). This regiochem-
t-
~
OC(0)OEt
p(oipr)2
OC(0)OEt
8
7
1. RCHO
2. H 2 0
1. RCHO
2. HZO
9, R’ = H, R2 = R
10
Scheme 2. Synthesis of 9 and 10
Table 1 Synthesis of 9, 10, 16, and 17 [a]
1
Entry Carbonate Carbonyl
cmpd.
R~CHO
5
2
Scheme 1. Synthesis of 2 and 5.
istry can be explained by the preference of the primary titanium
derivative 3 over the more congested intermediate 4 and its
reaction with aldehydes through a six-membered transition
state.[31However, the substituent R’ is a functional group containing a heteroatom that can strongly coordinate to titanium,
the equilibrium may be shifted in favor of the more hindered
regioisomer 4, thus providing the “terminal” addition product
5 by the reaction with aldehydes.r4.51
We postulated that ring strain might be another factor for
controlling the equilibrium between 3 and 4. Thus, we anticipated that the allyltitanium compound generated from 1 and the
ethyl carbonate derivative (6)of 1-vinylcyclopropanol[61would
exist mostly as the tertiary titanium derivative 7 but not as the
primary regioisomer 8 having the strained alkylidenecyclopropane fragment[*] (Scheme 2). The subsequent reaction with
aldehydes, therefore, would result in alkylidenecyclopropanes 9
(“terminal” adducts), which are widely employed starting materials or intermediates in organic synthesis.[’]
Our assumption proved to be correct. The reaction of 1 with
the carbonate 6 followed by treatment with EtCHO led to the
alkylidenecyclopropane 9a in high yield and the regioisomeric
vinylcyclopropane 10a in only 6 % yield (Table 1 , entry 1 ) . Similar results were obtained when PhCHO and Me,CO were used
[*I Prof. Dr. F. Sato, Dr. A. Kasatkin’+’
Department of Biomolecular Engineering, Tokyo Institute of Technology
4259 Nagatsuta-cho, Midori-ku, Yokohama, Kanagawa 226 (Japan)
Fax: Int. code +(45)924-5826
e-mail: fsato@;bio.titech.ac.jp
[‘I On leave from the Institute of Organic Chemistry, Ufa Research Center.
Russian Academy of Science.
2848
Q VCH Verlug.sgesel1schuft mhH, D-69451 Weinhelm.I996
6
6
6
11
13a
13a
13b
13b
13c
1
2
3
4
5
6
7
8
9
Products,
regioselectivity [“h][b]
Yield
[%I [cl
EtCHO
9 a (R’ = H, R’ = Et), 94; IOa, 6
PhCHO
9 b (R’ = H, R2 = Ph), 80, lob, 20
9 c (R’ = R2 = Me), >97
Me,CO
12, >97
65
EtCHO
PhCHO
16a (R’ = R 2= Ph), 93, 17a, 7 62
16b (R’ = Ph, R2 = Et), >97
EtCHO
16c (R’ = Hex, R2 = Et), >97
EtCHO
CH,O [dl 16d (R’ = Hex, Rz = H), >97
EtCHO
16e (R’ = Me& R’ = Et), 74, 17e. 26
76
84
40
65
14
80
45
[a] Titanium reagents were generated from 2.0 equiv [Ti(OiPr),] and 4.0 equiv
iPrMgCl in Et,O at -40 to -45 ‘C (1 h); then 2.0 equiv carbonyl compound was
added and the reaction mixture was stirred at -40 to -45°C for 1 b. [b] According
to * H N M Rdata of isolated regioisomeric mixtures. [c] Yields of isolated products
based on starting carbonares. [d] Et,O solution of monomeric CH,O prepared by
thermolysis of paraformaldehyde was used.
q;,
OH
6
9
11
12
16
10
R
13a,R = Ph
136.R = Hex
13c,R = Me3Si
17
instead of EtCHO (9 was the main product in both cases),
although the regioselectivity was somewhat dependent on the
nature of the carbonyl electrophile (entries 2 and 3) .[‘‘I
The fact that the reaction of 1 with ethyl 1-vinylcyclobutyl
carbonate (11) (the carbonate derivative of vinylcyclobutanol),
followed by treatment with EtCHO afforded exclusively the
vinylcyclobutane 12 (the usual “branched” adduct) strongly
demonstrates the principal role of the alkylidenecyclopropane
0570-0833/96/3523-2848$15.00+ .25/0
Angcw. Chem. Inr. Ed. Enxl. 1996,175. No. 23/24
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strain in controlling the regiochemistry observed here (Table I ,
entry 4).
The reaction of 1 with secondary or tertiary propargylic carbonates has been shown to provide allenyItitanium compounds
which, in turn, react with aldehydes to give homopropargyl
alcohols.[’ * I However. the results obtained by the reaction of 1
with 6 strongly suggested that the reaction with carbonate
would afford the
derivatives 13 of 1-alkynylcyclopropanols[61
propargyltitaniutn compounds 14 rather than the more strained
allenyltitaniums 15 as shown in Scheme 3.”*] Thus, the subse-
OC(0)OEt
13
i i p i Pr),
I
A1
15
14
i
1. R ~ C H O
2. HzO
OC(0)OEt
1. R%HO
2. H20
OH
R~*OH
17
16
Scheme 3. Synthesis of 16 and 17.
Keywords: cyclopropanes
compounds
-
propargyl compounds
*
titanium
A. Kasatkin, T. Nakagawa, S. Okamoto, F. Sato, J Am. Cheni. Suc 1995. 117,
3881.
M. T. Reetz. Top. Curr. Chenz. 1982, 106, 1; D. Seebach. B. Weidmann, L.
Widler, Modern Syntheric Methods. Transition Metals in Orgum(.Synthesis (Ed.
R. Scheffald), Otto Salle Verlag, Frankfurt, 1983, pp. 217--354: M. T. Reetz,
Organotiraniuni Reagent.\ in Organic S~nr17esi.r.Springer, Heidel berg, 1986.
R. W Hoffmann. Angen. Cheni. 1982, 94, 569: Angew Chem I n t Ed. Engl
1982. 21. 555: Y Yamamoto, Acc. Chem. Rrs. 1987. 20, 243.
R. Hanko, D. Hoppe, Angeir. Chem. 1982, 94, 378; Angeii. Chm7. Int. Ed.
Engl. 1982.21.372; B. Weidmann. D. Seebach, ;bid 1983.95. 12 and 1983.22,
31.
P. K Zubaidha. A. Kasatkin, F. Sato, J Chem. Soc. Cheni. Conimun. 1996,197.
1-Vinyl- and I-alkynylcyclopropanols were prepared by the reaction of 1ethoxycyclopropanol with two equivalents of vinyl- and aikynytmagneslum
bromides, respectively (see ref. 171); the successive treatment of the tertiary
alcohols with 1.1 equiv EtMgBr (Et,O, O’C. 5 min) and 1.2 equiv EtOC(0)CI
(20-C. 4 h) gave the carbonates 6 and 13 in 80-90% yield
J. R. Y. Salaun. Top. Curr. Chem. 1988, /44. 1.
The ring strain of methy~enecyciopropdneis 14 kcalmol-’ higher than that of
methylcyclopropane: A. Krief. Top. Cuvr Chem. 1987. 135. 35.
P. Binger. H. M. Buch. Top. Curr. Chum. 1987, 135, 77; T. Ohta. H. Takaya,
Comprehensive Organic Sinrhesis, Vol. 5 (Eds.. B. M. Trost, 1. Fleming),
Pergamon. Oxford, 1991, p- 1188. See also: S. Brise, S. Schomenauer, G.
McGaffin. A. Stolle, A. de Meijere, Chenz. Eur. J 1996, 2. 545. and references
therein
The related lithium derivatives prepared by the treatment of I-alkenyl-lmethylseleno-cyclopropanes with BuLi exhibited low regioselectivity in the
reaction with aldehydes. S. Halazy, A. Krief, Tetrahedron Lrrt. 1981. 22,4341.
T. Nakagawa. A. Kasatkin, F. Sato, Terrahedroii Lert. 1995,36. 3207. See also.
K. Furuta. M. Ishiguro. R. Haruta. N. Ikeda, H. Yamamoto. Bull. Chenz. Soc
Jpn 1984, 57. 2768.
It has been recently shown by using “C NMR spectroscopy that Iithiated
dicyclopropylacetylene exists exclusively as a propargyllithium (but not allenyllithium) compound. H. J. Reich, J. E.Holladay, J Am. Chem. Soc. 1995,
117, 8470.
To our knowledge, no general approach to compounds containing an 1alkenylidenecyclopropdne fragment has been developed so f‘ar. For a few examples of this type of compound prepared by using other methods. see: T.
Liese, A. de Meijere, Chem. Eer. 1986, ff9,2995: J. Al-Dula)ymi, M. S. Baird,
Tetrahedron Lett. 1988.29,6147. K. Tanaka, K. Otsubo, K. Fuji. Sjnlett 1995,
933.
It is noteworthy that lithiated 1-ethoxy-2-(trimethylsilylethynyl)cycIopropane
showed the opposite regioselectivity to afford only acetylenic addition products in the reaction with carbonyl compounds: H. C. Militzer. S. Schoemenauer, C. Otte. C. Puls. J. Hain, S. Braese, A. de Meijere, Svirhesis 1993, 998.
quent treatment with aldehydes would give the allenic cyclopropanes 16, which are of synthetic interest but are not readily
available by other
As expected, the reaction of 1
with the ethyl carbonate derivative 13a of I-(phenylethyny1)cyclopropanol followed by addition of PhCHO led primarily to the allenic cyclopropane 16a with only 7 YOyield of the
corresponding regioisomeric alkynylcyclopropane 17a (Table 1,
entry 5). Similarly, the treatment of the titanium reagents generated from the carbonates 13a-c with EtCHO and/or CH,O
afforded 16 exclusively (entries 6- 8) or predominantly (entry 9) .[I4]
Diastereoselective Addition of n-Butyllithium
to 2-Phenylpropanal: A Reassessment of the
Solvent and Temperature Effects**
Experimental Procedure
Gianfranco Cainelli,* Daria Giacomini,* P. Galletti,
and A. Marini
The following procedure for preparation of 9a and 10a (entry 1 in Table 1) is representative To a solution of [Ti(OiF’r),] (284mg. l.00mmol) and 6 (156mg,
0.50 mmol) in EtzO (7.5 mL) was added dropwise iPrMgCl (1.35 mL, 1.48 M in
Et,O, 2.00 mmo1)at -50 C. Thereactionmixturewasstirredat -4510 -40’Cfor
1 h, then EtCHO (58 mg. 1.00 mmol) was added. The reaction mixture was stirred
for 1 h at -45 to -40 ’C then hydrolyzed with a solution of water (1.2 mL) in T H F
(3.0 mL). warmed up to 20 C, and stirred for 30 min. The organic layer was decanted and the white solid was washed thoroughly with ether. The combined organic
layers were dried over MgSO, and concentrated under reduced pressure. After
separation by column chromatography (silica gel, hexane:EtOAc = 5 : I), a mixture
of 9a and 10a (4X mg. 76% total yield) was isolated as a colorless oil. ‘H N M R
(300 MHz, CDCI,): 9a: d = 0.97 (t. J = 6.3 Hz, 3 H ) , 1 09 (m. 2H). 1.43-1.70 (m,
10a:6=0.62(m,2H).2.95
4H).2.22- 2.48(m,ZH),3.67(m,lH),5.8O(m,lH);
(m, 1 H). 4.96 -5.03(m,2H),6.13 ( d d , J =16.8,10.2 Hz, 1 H). I 3 C N M R (75 MHz.
CDC13):9a:6=1 93.2.67.9.91,29.55,39.31,72.65,114.25,124.89;10a:~=11.02,
12.29. 27.90. 79.40, 113.57.
Received: June 10. 1996
Revised version: July 29, 1996 F29206JEJ
German version: Angew. Chem. 1996, 108, 3024-3025
Angew Chem. In!. Ed. Enyl. 1996. 35, No. 23/24
The mechanism of asymmetric induction in reactions ofa-chiral aldehydes and ketones has been a subject of continued speculation since Cram and Kopecky’s seminal work.[’] Among several factors that have been recognized to influence the n-facial
diastereoselectivity, the role of the solvent has hitherto been
underestimated.
[‘I Prof. Dr. G. Cainelli, Dr. D. Giacomini, P. Galletti. A. Marini
Dipartimento di Chimica “G: Ciamician”
Via Selmi 2, 1.40126 Bologna (Italy)
Fax: Int. code +(51)25-9456
e-mail: cainelli(2 ciamOl ciam.unibo.it
(**I This work was supported by Minister0 dell’ Universitl e dclla Ricerca Scientifica e Tecnologica (MURST) (fond; 60%) and the University of Bologna (fund
for selected topics). We thank Micaela Fabbri for performing the HPLC
analysis.
,c VCH Verlugsgesellsckafi mhH, 0.69451
Weinheim, 1996
+
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ally, efficiency, synthesis, carbonyl, reaction, compounds, alkylidenecyclopropanes, regioselectivity, unusual, derivatives, allenylpropargyltitanium
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