Synthesis of stereohomogeneous cyclopropanecarbaldehydes and cyclopropyl ketones by cycloalkylation of 4-hydroxy-1-alkenyl carbamates

Article abstract of DOI:10.1002/anie.200461136

Small rings: Only a few methods are known for the synthesis of cyclopropane carbaldehydes and cyclopropyl ketones 2. In a new, simple route to highly enantioenriched trisubstituted three-membered rings, 4-hydroxy-1-alkenyl N,N-di-isopropyl carbamates 1 are treated with NaH, resulting in migration of the carbamoyl group and intramolecular enolate alkylation.

Full text of DOI:10.1002/anie.200461136

Angewandte
Chemie
Cyclizations
Synthesis of Stereohomogeneous
Cyclopropanecarbaldehydes and Cyclopropyl
Ketones by Cycloalkylation of 4-Hydroxy-1-
alkenyl Carbamates**
Rainer Kalkofen, Sven Brandau, Birgit Wibbeling, and
Dieter Hoppe*
Only a few methods are known for the synthesis of optically
active cyclopropanecarbaldehydes and cyclopropyl ketones
by ring-forming reactions.[1–3] Taylor et al.[4] very recently
described the synthesis of several racemic,disubstituted
cyclopropanecarbaldehydes by intramolecular cycloalkyla-
tion of (Z)-4-hydroxy-2-alkenyl N,N-diisopropylcarbamates 1
by activation of the hydroxy group with trifluoromethanesul-
fonic anhydride (Tf2O; Scheme 1).
Scheme 2. Enantioselective synthesis of 4-hydroxy-1-alkenyl carbamates
4. 4g–p: R1 =Ph, 4a–f: R1 =H, R2, and R3 in Table 1.
During the course of our work we made a surprising
observation: simply treating the homoaldol adducts 4 with
sodium hydride furnished the cyclopropanes 8 with excellent
diastereoselectivity and complete chirality transfer (Meth-
od B,Scheme 3,Table 1). When alcohols
4 and sodium
hydride were heated in THF or DMF for several hours,the
cyclopropanes 8a–p formed smoothly with the same effi-
ciency as that observed for Method A. Apparently the N,N-
diisopropylcarbamoyl group in alkoxide 6 migrates to the O4
atom,[9] forming the (Z)-enolate 7,which undergoes cyclo-
alkylation by nucleophilic substitution of the carbamate
group with strict stereoinversion. The enolate moiety occu-
pies an anti position in transition state 7 in order to avoid
steric repulsion with R2 and R3. Method B also works well
Scheme 1. Cyclopropane formation according to Taylor et al.
Cb=CONiPr2, Tf=triflate.[4]
We found in our initial studies that this method can be
extended to the synthesis of optically active,trisubstituted
cyclopropanecarbaldehydes and cyclo-
propyl ketones 8 starting from compounds
4,which in turn are readily obtained by
enantioselective homoaldol reaction in the
presence of (À)-sparteine[5–7] (Scheme 2).
According to Taylor et al.,the ( Z)-anti
homoallylic alcohols 4 are converted into
the corresponding triflates 5,which
undergo immediate intramolecular attack
by the weakly nucleophilic enol carbamate
moiety.[8] The substitution step (Scheme 3,
Method A) proceeds with complete ster-
eoinversion,leading to a cis arrangement
of R2 and R3 and placing the acyl residue
into the trans position to both of them via
transition state 5.
Scheme 3. Synthesis of highly enantioenriched disubstituted cyclopropanes.
even when a formyl group is generated (Table 1,entries 3
and 5).
[*] Dipl.-Chem. R. Kalkofen, Dipl.-Chem. S. Brandau, B. Wibbeling,
Prof. Dr. D. Hoppe
Organisch-chemisches Institut
The relative configuration of 8h was confirmed by a
single-crystal X-ray analysis.[10] The absolute configuration of
the precursor 4 is retained at C3,and the ee values of the
products 8 correspond to those of the starting compounds 4
(Table 1). The combination of the cycloalkylation with the
(À)-sparteine-mediated homoaldol reaction results in a two-
step stereoselective route to cyclopropyl ketones.[11] The N,N-
diisopropylcarbamoyl group is required for the activation in
the deprotonation step of the homoaldol reaction. Moreover,
Westfälische Wilhelms-Universität Münster
Corrensstrasse 40, 48149 Münster (Germany)
Fax: (+49)251-83-36531
E-mail: dhoppe@uni-muenster.de
[**] This work was supported by the Deutsche Forschungsgemeinschaft
(SFB 424) and the Fonds der Chemischen Industrie. S. Brandau
thanks V. Trepohl for her skillful experimental assistance.
Supporting information for this article is available on the WWW
under http://www.angewandte.org or from the author.
Angew. Chem. Int. Ed. 2004, 43, 6667 –6669
DOI: 10.1002/anie.200461136
ꢀ 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
6667

Communications
Table 1:
Entry
Route
Solv.
Substr. (% ee)
Prod. (% ee)
R1
R2
R3
Yield [%]
d.r.
[a]2D0[a]
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
A
A
B
A
B
A
A
A
A
B
A
B
A
B
B
B
B
B
B
B
B
B
CH2Cl2
CH2Cl2
DMF
CH2Cl2
DMF
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
THF
CH2Cl2
DMF
CH2Cl2
THF
DMF
THF
4a (30)[b]
4b (71)[b]
4b (71)[b]
4c (87)[b]
4c (87)[b]
4d (82)[c]
4e (83)[c]
4 f (86)[c]
4g (96)[b]
4g (92)[b]
4h (93)[b]
4h (95)[b]
4i (91)[b]
4i (93)[b]
4 f (86)[b]
4j (94)[b]
4k (92)[e]
4l (91)[b]
4m (95)[b]
4n (96)[b]
4o (95)[b]
4p (95)[b]
8a (30)[c]
8b (71)[c]
8b (71)[b]
8c (87)[c]
8c (87)[b]
8d (82)[c]
8e (83)[c]
8 f (>80)[c]
8g (96)[b]
8g (91)[b]
8h (93)[b]
8h (94)[b]
8i (91)[b]
8i (93)[b]
8 f (>80)[b]
8j (92)[b]
8k (92)[e]
8l[f]
H
H
H
H
H
H
H
H
Ph
Ph
Ph
Ph
Ph
Ph
H
Ph
Ph
Ph
Ph
Ph
Ph
Ph
(CH2)2CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
(CH2)2Ph
Ph
Ph
(CH2)2Ph
(CH2)2Ph
CH(CH3)2
cyclopropyl
(CH2)4CH3
Ph
70
>99
71
48
58
>99
39
61
80
98
83
64
41
91
62
84
98
84
98:2
95:5
95:5
95:5
98:2
98:2
88:12
98:2
98:2
98:2
98:2
98:2
92:8
98:2
98:2
98:2
98:2
98:2
98:2
98:2
98:2
98:2
+2
+110
+110
+3
+3
À4
[d]
–
+1
+153
+142
À17
À17
+148
+151
+1
+206
+177
–
À85
À19
À50
À9
Ph
C(CH3)3
C(CH3)3
p-BrC6H4
p-BrC6H4
(CH2)4CH3
naphthyl
furyl
THF
THF
THF
DMF
THF
CH3
8m[g]
CH2CH3
CH(CH3)2
cyclopropyl
cyclohexyl
96
62
74
78
8n (96)[b]
8o (95)[b]
8p (95)[c]
THF
[a] c=0.15–0.92, CHCl3. [b] Determined by HPLC, column: Chira Grom-2. [c] Determined by chiral GC, column: b-Dex 120. [d] Due to the volatility of
the compound it was not possible to determine the specific optical rotation. [e] Determined by HPLC, column: Chira Grom-1, solvent: n-hexane/
isopropyl alcohol. [f] Achiral. [g] Not determined.
through the carbamoyl migration both the nucleophilic and
the electrophilic properties of the stable precursors 4 are
activated. These features fulfill in an exemplarily manner one
demand of modern organic synthesis,namely minimizing the
number of steps in a synthetic sequence.[12]
Keywords: asymmetric synthesis · cyclization · cyclopropanes ·
synthetic methods
.
[1] Reviews: a) R. E. Taylor,F. Engelhardt,F. C. Schmitt,M. J.
Schmitt, Tetrahedron 2003, 59,5623; b) H. Lebel,J.-F. Marcoux,
C. Molinario,A. B. Charette, Chem. Rev. 2003, 103,977; c) W.
Kirmse, Angew. Chem. 2003, 115,1120; Angew. Chem. Int. Ed.
2003, 42,1088.
Experimental Section
Synthesis of cyclopropanecarbaldehydes and cyclopropyl ketones:
Method A: A flame-dried flask was charged with 4b (199 mg,
0.3 mmol,1 equiv) in 10 mL CH 2Cl2 under an argon atmosphere. 2,6-
Lutidine (140 mg,1.3 mmol,4 equiv) was added by syringe,the
solution was cooled to À788C,and then freshly distilled triflic
anhydride (314 mg,1.1 mmol,3 equiv) was injected. The reaction
mixture was stirred for 1 h,quenched with 1 mL water,and allowed to
warm to room temperature. The mixture was diluted with 25 mL
CH2Cl2,the aqueous phase was separated,and the organic layer was
washed with saturated NaHCO3 solution (1 ” 10 mL). The organic
phase was dried over MgSO4 and the solvent evaporated in vacuum.
The crude product was purified by flash chromatography on silica gel
(diethyl ether/n-pentane 1:10).
Method B: To the anti-homoaldol adduct 4i (169 mg,0.37 mmol,
1 equiv) was added sodium hydride (60% in mineral oil; 20 mg,
0.5 mmol,1.35 equiv). The flask was placed under argon,THF (2 mL)
was injected,and the resulting solution was heated for 14 h at 60 8C.
When DMF was used as the solvent the solution was stirred 1 h at
room temperature and then heated for 2–12 h at 608C (tlc control).
For workup 10 mL saturated sodium chloride solution was added. The
aqueous phase was separated and extracted with diethyl ether (3 ”
25 mL). The combined organic extracts were dried over MgSO4 and
the solvents evaporated in vacuum. The crude product 8i was purified
by flash chromatography on silica gel (diethyl ether/n-pentane 1:5).
For yields and enantiomeric excesses see Table 1.
[2] a) H. Abdallah,R. GreØ,R. CarriØ, Tetrahedron Lett. 1980, 23,
503; b) H. M. Walborsky,L. E. Allen Tetrahedron Lett. 1969, 11,
823; c) V. A. Aggarwal,E. Alonso,G. Fang,M. Ferra,G. Hynd,
M. Porcelloni, Angew. Chem. 2001, 113,1482; Angew. Chem. Int.
Ed. 2001, 40,1433; d) K. Yamaguchi,Y. Katzuta,H. Abe,A.
Matsuda,S. Shuto, J. Org. Chem. 2003, 68,9255.
[3] For other examples of asymmetric syntheses of cyclopropane
derivatives mediated by (À)-sparteine see: a) M. Paetow,F.
Hintze,D. Hoppe, Angew. Chem. 1993, 105,430; Angew. Chem.
Int. Ed. Engl. 1993, 32,394; b) M. Paetow,M. Kotthaus,M.
Grehl,R. Fröhlich,D. Hoppe, Synlett 1994,1034; c) S. Wiede-
mann,A. de Meijere,I. Marek, Synlett 2002,679.
[4] a) R. E. Taylor,C. A. Risatti,F. Engelhardt,F. Conrad,M. J.
Schmitt, Org. Lett. 2003, 5,1377; b) Prof. Taylor informed us
after submission of our manuscript that he could successfully
apply his cyclization conditions also to enantioenriched,higher
substituted homoaldol products.
[5] Reviews: a) D. Hoppe,T. Hense, Angew. Chem. 1997, 109,2376;
Angew. Chem. Int. Ed. Engl. 1997, 36,2282; b) “Organolithiums
in Enantioselective Synthesis”: D. Hoppe,F. Marr,M. Brügge-
mann in Topics in Organometallic Chemistry, Vol. 5 (Ed.: D. M.
Hodgson),Springer,Berlin, 2003,p. 61; c) “Organolithiums in
Enantioselective Synthesis”: P. Beak,T. A. Johnson,D. D. Kim,
S. H. Lim in Topics in Organometallic Chemistry, Vol. 5 (Ed.:
D. M. Hodgson),Springer,Berlin, 2003,p. 134.
[6] a) D. Hoppe,O. Zschage, Angew. Chem. 1989, 101,67; Angew.
Chem. Int. Ed. Engl. 1989, 28,69; b) M. Özlügedik,J. Kristensen,
Received: June 30,2004
6668
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www.angewandte.org
Angew. Chem. Int. Ed. 2004, 43, 6667 –6669

Angewandte
Chemie
B. Wibbeling,R. Fröhlich,D. Hoppe, Eur. J. Org. Chem. 2002,
414.
0.1(4),max. residual electron density 0.09 ( À0.12) eŠÀ3,hydro-
gens calculated and refined as riding atoms. Data set was
collected with a Nonius KappaCCD diffractometer. Programs
used: data collection COLLECT (Nonius B. V., 1998),data
reduction Denzo-SMN (Z. Otwinowski,W. Minor, Methods
Enzymol. 1997, 276,307 – 326),absorption correction SORTAV
(R. H. Blessing, Acta Crystallogr. Sect. A 1995, 51,33 – 37; R. H.
Blessing, J. Appl. Crystallogr. 1997, 30,421 – 426),structure
solution SHELXS-97 (G. M. Sheldrick, Acta Crystallogr. Sect. A
1990, 46,467 – 473),structure refinement SHELXL-97 (G. M.
Sheldrick,Universität Göttingen, 1997),graphics SCHAKAL
(E. Keller, 1997). CCDC-240544 contains the supplementary
crystallographic data for this paper. These data can be obtained
free of charge via www.ccdc.cam.ac.uk/conts/retrieving.html (or
from the Cambridge Crystallographic Data Centre,12,Union
Road,Cambridge CB21EZ,UK; fax: ( + 44)1223-336-033; or
deposit@ccdc.cam.ac.uk).
[7] a) M. Seppi,R. Kalkofen,J. Reupohl,R. Fröhlich,D. Hoppe,
Angew. Chem. 2004, 116,1447; Angew. Chem. Int. Ed. 2004, 43,
1423; b) J. Reuber,R. Fröhlich,D. Hoppe, Org. Lett. 2004, 6,783.
[8] For the direct reaction of vinyl carbamates as enolate equiv-
alents: T. Krämer,C. F. Erdbrügger,E. Eggert, Tetrahedron Lett.
1989, 30,1233.
[9] For the generation of intermediate allenolates by carbamoyl
migration: a) C. Schultz-Fademrecht,M. Tius,S. Grimme,B.
Wibbeling,D. Hoppe, Angew. Chem. 2002, 114,1610; Angew.
Chem. Int. Ed. 2002, 41,1532; b) M. Zimmermann,B. Wibbeling,
D. Hoppe, Synthesis 2004,765.
[10] X-ray crystal structure analysis of 8h: C15H20O, Mw = 216.31,
colorless crystal 0.50 ” 0.15 ” 0.10 mm, a = 5.975(1), b =
10.359(1), c = 11.161(1) Š, b = 103.30(1)8, V= 672.3(1) Š3,
1calcd = 1.069 gcmÀ3, m = 4.96 cmÀ1,empirical absorption correc-
tion (0.790 ꢀ Tꢀ 0.952), Z = 2,monoclinic,space group
P21
[11] For related work,see the following Communication in this issue:
C. A. Risatti,R. E. Taylor, Angew. Chem. 2004, 116,6839;
Angew. Chem. Int. Ed. 2004, 43,6671.
[12] B. M. Trost, Angew. Chem. 1995, 107,285; Angew. Chem. Int. Ed.
Engl. 1995, 34,259.
(No. 4), l = 1.54178 Š, T= 223 K, w and f scans,3002 reflections
collected (Æ h, Æ k, Æ l),[(sin q)/l] = 0.59 ŠÀ1,1640 independent
(Rint = 0.036) and 1590 observed reflections [I ꢁ 2s(I)],149
refined parameters, R = 0.039, wR2 = 0.111,Flack parameter
Angew. Chem. Int. Ed. 2004, 43, 6667 –6669
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