Current Fluoroorganic Chemistry - American Chemical Society

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Chapter 28

Asymmetric Synthesis of β-Trifluoromethylated β-Amino Carbonyl Compounds Based on the 1,2-Addition to Trifluoroacetaldehyde SAMP- or RAMP-Hydrazones 1

1

1

Kazumasa Funabiki , Masashi Nagamori , Masaki Matsui , Gerhard Raabe , and Dieter Enders 2

2

1

Department of Materials Science and Technology, Faculty of Engineering, Gifu University, 1-1, Yanagido, Gifu 501-1193, Japan Institut für Organische Chemie, Rheinisch-Westfälische Technische Hochschule, Professor-Pirlet-Strasse 1, 52074 Aachen, Germany 2

An efficient asymmetric synthesis of α-trifluoromethyl substituted primary amines via nucleophilic 1,2-addition of alkyl-, phenyl- and allyl-lithium reagents to trifluoro acetaldehyde SAMP- or RAMP-hydrazones, followed by benzoylation and SmI-promoted nitrogen-nitrogen single bond cleavage is described. Asymmetric synthesis of trifluoromethylated β-amino aldehydes, carboxylic acids, and esters as well as γ-aminoalcohol via the oxidation of the obtained chiral α-trifluoromethylated homoallylamines is also described. 2

© 2007 American Chemical Society

In Current Fluoroorganic Chemistry; Soloshonok, V., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 2007.

447

448


Introduction

Because of their importance in pharmaceutical research based on the special electronic properties of the trifluoromethyl group, much attention has been addressed to the development of the efficient and enantioselective synthesis of a-trifluoromethylated amines (I) as well as a- or (3-trifluoromethylated amino acid derivatives (2,3). The 1,2-addition of organometallic reagents to C N double bonds is one of the most efficient routes to a-branched amines (4). Among them, the asymmetric 1,2-addition reaction using commercially available (S)- or (/?)-l-amino-2(methoxymethyl)pyrrolidine ( S A M P or R A M P , respectively) as a chiral auxiliary provides a promising synthetic route to enantioenriched amines (5). In this chapter, the asymmetric synthesis of a-trifluoromethylated amines based on the nucleophilic 1,2-addition of alkyl-, phenyl-, and allyl-lithium reagents to trifluoroacetaldehyde S A M P - or RAMP-hydrazones as well as the (3trifluoromethylated P-amino acids via the oxidation of the obtained atrifluoromethylated homoallylamine derivative, as described in in Figure 1.

O

O

x N' F

3

Pli

J C

"OMe

F

3

NH

O

F,CT

C ^ R

| ee = 97 - >99%] Ph

1

OH

NH

0

F j C ^ ^ O M e 0

x Pli

NH

F HN F C 3

C

3

O

^

^

H

O R

"OMe F . C ^ R

x

OMe Pli F

NH

3

C

OH ^

Figure 1. Asymmetric Synthesis of ^Trifluoromethylated j3-Amino Carbonyl Compounds Based on the 1,2-Addition to Trifluoroacetaldehyde SAMP-or RA MP-Hydrazones


449

Preparation of of Trifluoroacetaldehyde Hydrazones (6)


Trifluoroacetaldehyde S A M P - or RAMP-hydrazones 2 or V were readily obtained in 83% and 66% yields from commercially available trifluoroacet aldehyde ethyl hemiacetal 1 and S A M P or R A M P , respectively, in the presence of a catalytic amount of /?-toluenesulfonic acid (p-TsOH) in benzene. Trifluoro acetaldehyde morpholinohydrazone 3 was prepared in the same manner in 58% yield (Figure 2).

SAMP

(S)

H,N'

~OMe cat./?-TsOH OMe

benzene, reflux, 5 h OH RAMP F

C ^ O E t

3

H,N

JO /

(83%)

(R)

~OMe cat. p - T s O H Jl

benzene, reflux, 5 h F C 3

"^OMe 2

,

(66%)

O H N 2

OH

JL

F C 3

cat. /7-TsOH OEt

benzene

N' F C 3

1

reflux, 5 h

3

O (58%)

Figure 2. Preparation of Trifluoroacetaldehyde SAMP-, RAMP-, and Morphirino Hydrazones

Trifluoroacetaldehyde SAMP-hydrazone is much more stable than the corresponding imines and this would be the reason why the hydrazone can be purified by flash column chromatography. Very recently, Brigaud reported the preparation of other chiral trifluoro acetaldehyde hydrazone, as shown in Figure 3. In this reaction, the use of acidic catalyst produced the desired chiral hydrazone 5 along with the 1,3,4-oxadiazine derivative 6, because of the presence of a hydroxyl group. Neutral conditions without acidic catalyst afforded only the hydrazone 5 in quantitative yield (7).


450 Bn

° 1

E t

J HO^ ^

t 0 , U e n e

Bn

F C HO

F

3 3

3

C

5

X

0 ^ 6


Figure 3. Preparation of Other Chiral Trifluoroacetaldehyde Hydrazone

1,2-Addition of Alkyllithums to Trifluoroacetaldehyde S A M P or RAMP-hydrazones

Optimization of the Reaction Conditions of 1,2-Addition (6) First, we examined the screening of the reaction conditions of nucleophilic 1,2-addition to trifluoroacetaldehyde S A M P hydrazone 2 with commercially available tf-buthyllithium (tf-BuLi). When 3 equiv of w-BuLi were added slowly to an E t 0 solution of 2 at -78 °C and the reaction mixture was gradually warmed up to room temperature, a low yield (36%) of the product 7a was obtained together with a complex mixture, probably due to the low stability of trifluoromethylated lithium hydrazide (Figure 4, Table 1, entry 1). 2

w-BuLi

OMe

solvent '

F 3

c^ -Bu^

0 M e

w

7a

Figure 4.

Treatment of 2 with 1.5 equiv of «-BuLi in E t 0 at low temperature (78 °C) for a shorter reaction time (1 h) gave trifluoromethylated hydrazine 7a in 63% yield (entry 2). The use of 3 equiv of w-BuLi gave a higher yield (entry 3). Employing T H F as a reaction solvent resulted in unsatisfactory yields of 7a with decrease in diastereoselectivities (entries 4 and 5). The major diastereoisomer was readily separated by flash column chromatography. 2


451 Table 1. Screening of the Reaction Conditions of Nucleophilic 1,2Addition of Ai-BuLi 0

Entry d

\

2 3 4 5


C

n-BuLi

Solvent

Yield (%)

3 1.5 3 1.5 3

Et 0 Et 0 Et 0 THF THF

36 63 79 43 (37) 45 (39)

2

2

2

h

De (%)" >96 (>98) >96(>98) >96 (>98) 82 (>98) 82 (>98)

a

The reactions were carried out with trifluoroacetaldehyde SAMP-hydrazone 2 at -78 °C for 1 h. * Yields of isolated pure products. Values in parentheses are for the major diastereomer. Measured by F NMR before isolation. Values in parentheses after column chromatography. After w-BuLi was added at -78 °C, the reaction mixture was warmed up to room temperature overnight. 0

19

d

1,2-Addition of Various Alkyllithums and Phenyllithium (6) The results of the reaction of 2 with various alkyllithiums as well as phenyllithium (PhLi) are summarized in Table 2 (Figure 5).

Figure 5. Commercially available alkyllithiums, such as «-BuLi and w-hexyllithium, reacted well in the nucleophilic 1,2-addition to give the corresponding trifluoromethylated hydrazines 7a,a',d in good yields with excellent diastereoselectivities (entries 1, 2, and 5). Ethyllithium and tf-propyllithium, easily prepared from /-butyllithium (/-BuLi) and the corresponding iodoalkane (8), also reacted with hydrazone 2 to provide the corresponding hydrazines 7c and d in 48 and 65% yields, respectively (entries 3 and 4). Treatment of 2 with /-BuLi gave a moderate yield of 7e in moderate de (entry 6). However, the diastereomer could be readily separated by column chromatography affording diastereomerically pure 7e. When hydrazone 2 was treated with PhLi under the same conditions, 15% of the product 2f was obtained in 86% de along with a complex mixture of by-products (entry 7). Unfortunately, even in the presence


452 Table 2. Reaction of Trifluoroacetaldehyde S A M P - or RAMP-Hydrazones Entry" 1 2 3 4 5 6 7

R «-Bu w-Bu Et' «-Pr w-Hex /-Bu Ph


d

c

De (%/ >96(>98) >96(>98) >96 (>98) >96(>98) >96 (>98) 72 (>98) 86 (88)

b

Product 7a 7a' 7b 7c 7d 7e 7f

Yield (%) 79 74 48 65 68 58 (50) If/

a

The reactions were carried out with trifluoroacetaldehyde SAMP-hydrazone 2 and RLi (3 equiv) in Et 0 at -78 °C for 1 h. * Yields of isolated products. Values in parentheses are for the major diastereomer. Measured by F NMR before isolation. Values in parentheses after column chromatography. Trifluoroacetaldehyde RAMP-hydrazone V was used instead of SAMP-hydrazone 2. Prepared from /-BuLi and the corresponding iodoalkane. * There were many unidentified by-products in the F NMR of the crude reaction mixture. 2

c

19

d

e

l9

Figure 6.


453 of the trifluoromethyl group, the reaction of 2 with 3 equiv of methyllithium (MeLi) in E t 0 or toluene at -78 °C did not proceed efficiently giving only a small amount of the product together with recovery of 2 (58-75%). Raising the reaction temperature from -78 °C to room temperature in analogy to fluorinefree hydrazones as well as using methylmagunesium iodide at -20 °C or methycerium chloride (MeCeCl ) at -78 °C in place of M e L i did not improve the reaction. The absolute configuration of the stereogenic center generated by the 1,2addition using S A M P was established unambiguously as R by X-ray crystallography of 7e (Figure 6). 2


2

1,2-Addition of Prepared Allyllithium (9) For the screening of the allylation reaction of trifluoroacetaldehyde hydrazones, the reaction between trifluoroacetaldehyde morpholinohydrazone 3 and tetraallyltin was first examined. The results are summarized in Table 3 (Figure 7).

Z ^ l S n V

U

_ P h L i

1

Et 0

Et 0

rt, 1 h

-78 ° C , 3 h

2

2

^ F

3

C

1

^

^

^

8

Figure 7.

Treatment of tetraallyltin (3 equiv) with PhLi (12 equiv) at room temperature, followed by addition of trifluoroacetaldehyde morpholino hydrazone 3 at -78 °C, gave the corresponding trifluoroacetaldehyde morpholinohydrazine 8 in 62% yield (entry 4). The reaction of 3 with 3 equiv each of tetraallyltin and PhLi was extremely sluggish, providing only a trace amount of 8 (entry 1). Employing tetraallyltin (1-2 equiv) and PhLi (4-8 equiv) produced 8 in 21-47% yields along with the recovery of 3 (entries 2 and 3). The use of allyltriphenyltin (3 equiv) in place of tetraallyltin with PhLi (3 equiv) was also ineffective, giving 8 in 20% yield together with 15% of 3. Yb(OTf) catalyzed (5 mol %) allylation with 0.3 equiv of tetraallyltin in acetonitrile at room temperature did not occur at all, and 3 was recovered in quantitative yield (10). With other allylic nucleophiles e.g., allylmagnesium bromide (3 equiv, 78 °C to rt, overnight), only a trace amount of 8 was formed with 67% recovery of3. 3


454 Table 3. Screening of the Reaction Conditions of Allylation of Trifluoroacetaldehyde Morpholinohydrazone


Entry" 1 2 3 4

(CH =CHCH )jSn 3 1 2 3 2

b

Yield (%) 7(38) 21 (35) 47 62

PhLi (equiv) 3 4 8 12

(equiv)

2

a

The reactions were carried out with trifluoroacetaldehyde morpholinohydrazone 3, (CH =CHCH ) Sn, and PhLi at -78 °C for 1 h. Yields of isolated pure products. Values in parentheses are for the recovery of starting hydrazone. b

2

2

4

Next, in order to synthesize diastereo- and enantiomerically pure hydazines, the stereoselective allylation of trifluoroacetaldehyde S A M P - or R A M P hydrazone 2 or 2' was carried out (Figure 8) (11). When SAMP-hydrazone (5)2 was treated with a mixture, obtained by the reaction between 3 equiv o f tetraallyltin and 12 equiv of PhLi at room temperature, in E t 0 at-78 °C for 4 h, the allylated hydrazine 7g was produced with high diastereoselectivty (93 : 7), and diastereomerically pure 7g was easily obtained by flash column chromatography in 80% yield. RAMP-hydrazone V also nicely underwent the 2

^

.

°

M

e

H N '

N

^ ) 93:7(>98% OMe

92

8(>98%t/e)

(S)

Et 0 2

-78 ° C , 4 h 7 g » (67%)

a

D e t e r m i n e d by

,

9

F N M R before isolation

V a l u e s in parentheses after c o l u m n chromatography.

Figure 8. Reaction of Trifluoroacetaldehyde SAMP- or RAMP-Hydrazones with Prepared Allyllithium


a

455 allylation reaction to give 7g' (>98% de) in 67% yield after column chromatography.

Asymmetric Synthesis of a-Trifluoromethylated Amines


Benzoylation of Trifluoroacetaldehyde SAMP-Hydrazines (6,9) Benzoylation of trifluoroacetaldehyde S A M P - or RAMP-hydrazines 7, having fl-butyl, ^-propyl, «-hexyl, allyl, or phenyl groups, was carried out with an excess amount of triethylamine (10 equiv) and benzoyl chloride (10 equiv) in the presence of a catalytic amount of 4-dimethylaminopyridine (DMAP) at room temperature, to give the corresponding hydrazides in good to excellent yields (Figure 9). However, the reaction of trifluoroacetaldehyde SAMP-hydrazine 7 with a /butyl group did not proceed at all under this reaction conditions, and the starting hydrazine 7 was recovered quantitatively. It was found that lithium hydrazide, easily prepared from trifluoroacetaldehyde SAMP-hydrazine 7e with 1.2 equiv of H - B u L i at -78 °C, smoothly reacted with 1.2 equiv of benzoyl chloride in a shorter reaction time, to produce 9e in 66% yield (Figure 9).

P h C O C l , E t N , cat. 3

DMAP Ph'

OMe

R = w - B u , « - P r , w-Hex, A l l y l , P h

7

9 (62-97%)

1) « - B u L i , - 7 8 ° C , 10 min 2) P h C O C l , -78 ° C to rt, overnight OMe

9e

7e

(66%)

Figure 9. Benzoylation of Trifluoroacetaldehyde SAMP- or RAMP-Hydrazines with Benzoyl Chloride and Et N 3


456 Sml -Induced Nitrogen-Nitrogen Single Bond Cleavage (6,9) 2

Three equiv of S m l (12) in the presence of l,3-dimethyltetrahydro-2(l//)pyrimidinone (DMPU) in T H F at room temperature for 30 min afforded the (R)7V-benzoyl a-trifluoromethylated amines 10 without detectable epimerization or racemization (Figure 10, Table 3). Various S A M P - or RAMP-hydrazides 9 participated successfully in the reaction to provide the corresponding amides 10 in good to excellent yields with excellent ee (up to >99%). The reaction in MeOH gave a trace amount of the Downloaded by STANFORD UNIV GREEN LIBR on September 27, 2012 | http://pubs.acs.org Publication Date: January 11, 2007 | doi: 10.1021/bk-2007-0949.ch028

2

O Sml

2

PrT OMe

NH

THF-DMPU (v/v = 4:l)

rt, 30

F C

R

3

min 10

Figure 10. Sml -Induced Cleavage of the N-N Single Bond of Trifluoromethylated SAMP- or RAMP-Hydrazides 2

Table 3. Sml -Induced Cleavage of the N-N Single Bond of Trifluoromethylated SAMP- or RAMP-Hydrazides 2

Entry" 1 2 3 4 5 6 7 8 d

e

R n-Bu n-Bu w-Bu n-Pr «-Hex t-Bu Ph Allyl

Product 10a 10a 10a' 10c lOd lOe lOf 10g

b

Yield (%) 87 4(90) 95 83 97 71 73 75

c

Ee (%) 98 -

97 98 98 >99 88 >99

a

The reactions were carried out with hydrazide 9 and Sml (3 equiv) in the presence of DMPU in THF at room temperature for 30 min. Yields of isolated products. Values in parentheses are for the recovery of 9. Measured by HPLC analysis using a chiral stationary phase column (DAICEL OD or (S,S)-Welk-0, 1-heptane/2-propanol = 9/1 or 95/5). MeOH was used as a solvent in the absence of DMPU. *RAMP-hydrazide 9a' was used. 2

c

d


457 product 10, together with recovery of the starting hydrazide (90%). This method using Sml2 also effective for cleavage of nitrogen-nitrogen single bond of other chiral S A M P hydrazides, such as heteroaromatic substituted S A M P hydrazide (13) and TV-SAMP 3-substituted 3,4-dihydro-2//-isoquinolin-l-one (14). The benzoyl group is essential for the cleavage of nitrogen-nitrogen single bond of 9. Thus, treatment of SAMP-hydrazine 7g with S m l (3 equiv) under the same conditions gave only a trace amount of the corresponding amine, and hydrazine 7g was recovered in 84% yield (Figure 11). Downloaded by STANFORD UNIV GREEN LIBR on September 27, 2012 | http://pubs.acs.org Publication Date: January 11, 2007 | doi: 10.1021/bk-2007-0949.ch028

2

Figure 11. Sml -Induced Cleavage of the N-N Single Bond of Trifluoromethylated SAMP- or RAMP-Hydrazides 2

Very recently, Friestad has examined the relationship between the protecting groups of the hydrazines and Sml (15). Consquently, it was found that the use of a trifluoroacetyl group as a protecting group resulted in the effective cleavage of nitrogen-nitrogen single bond of the hydrazides via the chelation of fluorine atom(s) and Sm metal. 2

Asymmetric Synthesis of p-Trifluoromethylated P-Amino

Carbonyl Compounds via Oxidation of a-Trifluoromethylated Homoallyl Amines (16)

As shown in Figure 12, the ozonolysis of (R)-N-benzoy\-atrifluoromethylated homoallylamine lOg thus prepared in the presence of 2.5 M NaOH (6 equiv) methanol solution in dichloromethane at -78 °C smoothly proceeded to produce the corresponding (/?)-(3-jV-benzoylamino-Ptrifluoromethylated carboxylic acid methyl ester 11 in 69% yield with slight racemization (17). Other enantiomer 10g' also participated well in the ozonolysis to produce the 11' in 49% yield with 96% ee. The strong electronegativity of the trifluoromethyl group seems to have an effect on the epimerization of the starting hydrazone or the product under the basic conditions.


458 Direct synthesis of acid 12' using the combination of 1 equiv of potassium permanganate ( K M n Q ) and 10 equiv of sodium periodinate (NaI0 ) has been carried out. The oxidation proceeded smoothly at room temperature to give the corresponding P-benzoylamino-p-trifluoro-methylated carboxylic acid 12' in 65% yield. Its enantiomer ratio could be determined by esterification using chlorotrimethylsilane in methanol leading to methyl ester 11' (18), as 94% ee. Finally, the carbon-carbon double bond of (/?)-Af-benzoyl-a-trifluoromethylated homoallylamine lOg was successfully cleaved with a catalytic amount (1 mol%) of osmium tetroxide (Os0 ) using N a I 0 (4 equiv) as the stoichiometric oxidant, to produce the corresponding P-benzoylamino-Ptrifluoromethyl aldehyde 13 in 92% yield with >99% ee. The aldehyde 13 is stable enough to easily separate by normal flash chromatography. The Nbenzoyl group will play a crucial role in the stability of the aldehyde like the /?tolylsulphinyl (19), N-Z-butoxycarbonyl (Boc) (20), or carboxybenzyloxy (Cbz)(21) groups on the reported fluorine-free aldehydes. The reduction of the aldehyde 13 with 0.5 equiv of sodium borohydride (NaBH ) in EtOH at room temperature for 4 h produced the quantitative yield of the corresponding enantiopure trifluoromethylated y-amino alcohol 14 without epimerization (Figure 13). 4

4


4

4

4

Conclusions

In summary, we have succeeded in the highly enantioselective synthesis of a-trifluoromethylated amines through the 1,2-addition of various organolithium species to trifluoroacetaldehyde S A M P - or RAMP-hydrazones and subsequent SmI -promoted cleavage of the nitrogen-nitrogen single bond. Furthermore, we have demonstrated that asymmetric synthesis of trifluoromethylated P-amino aldehyde, carboxylic acid, and ester as well as y-aminoalcohol via the oxidation of chiral a-trifluoromethylated homoallylamine obtained. 2

Acknowledgements

K.F. is grateful to the Alexander von Humboldt Foundation for a postdoctoral fellowship (2000-2001). We thank Degussa A G , B A S F A G , Bayer A G , and Aventis for the donation of chemicals. We also thank the Central Glass Co., Ltd., for the gift of trifluoroacetaldehyde ethyl hemiacetal and hydrate. This work has been supported by the Saijiro Endo Foundation. We also thank Dr. J. Runsink for measuring the F N M R spectra. We thank Professors Hiroki 19


459

o

o

X

0 , NaOH

1

3

P h ^ N H

^

P h ^ N H

CH Cl -MeOH(v/v=10/l) 2

0

5

2

-78 ° C , 3 0 m i n

JJ

F j C ^ ^ O M e

10g >99%ee

11(69%) n

A

0

/

94% 0

O

X

3


N H JL 3

C

* > ^

CH CI -MeOH(v/v= 2

(S)

"

7

8

°

c

>

3

0

0 1 1 1 1

F

3

3

C

A 0

( 5 K ^

10g'

11' (49%) 96% e**

0

F

O

JL

10/1)

2

>99%ee

A

p h

A P h ^ N H

0 , NaOH

Pli

F

a

ee

A

M

e

O

N H

KMnQ -NaIQ 4

JL ^99% eg

94%

ee

0 cat. O s 0

NaI0

4

11

4

P I T ^ H T H F - H 0 ( v / v = 1:1)

T H F - H 0 ( v / v = 1:1)

rt, 5 m i n

it, 2 h

2

lOg >99%

0

2

13 (92%)

ee

>99%

ee

Figure 12. Asymmetric Synthesis of P-Benzoylamino-f$-trifluoromethylated Carboxylic Acid Esters, Carboxylic Acid, and Aldehyde

o x P l T ^ H p

3

C

O

- ^ \ X ^ 13 >99%

NaBH H

4

E t O H , rt, 4 h 14 (99%)

ee

>99%

ee

Figure 13. Asymmetric Synthesis of y-Trifluoromethylated y-Amino Alcohol


460 Yamanaka, Takashi Ishihara, and Tsutomu Konno of the Kyoto Institute of Technology for the HRMS measurement.

References


1.

For recent reviews on asymmetric synthesis of functionalized αtrifluoromethylated chiral amines using chiral auxiliary, see: (a) Bravo, P.; Zanda, M. In Enantiocontrolled Synthesis of Fluoro-organic Compounds,

Soloshonok, V. Α., Ed.; John Wiley & Sons: Chichester, 1999; pp 107-160. (b) Bravo, P.; Bruche, L.; Crucianell, M.; Viani, F.; Zanda, M. In Asymmetric Fluoroorganic Chemistry: Synthesis, Application, and Future

2.

Directions, Ramachandran, P. V., Ed.; ACS Symposium Series 746, Washington, DC, 1999; pp 98-116. (c) Soloshonok, V. A. In ref. lb; pp 7483. (d) Ishii, Α.; Kanai, M.; Katsuhara, M. In Fluorine-ContainingSynthons, Soloshonok, V. Α., Ed.; ACS Symposium Series 911, Washington, DC, 2005; pp 368-377. (e) Bonnet-Delpon, D.; Bégué, J.-P.; Crousse, B. In ref. 1d; pp 412-429. For a recent book for fluorinated amino acid, see: Fluorine-containing Amino Acids : Synthesis and Properties, Kukhar' V. P.; Soloshonok, V. Α.,

3.

4.

Eds.; John Wiley & Sons: Chichester, 1995. For recent reviews on asymmetric synthesis of functionalized fluorinecontaining amino acids see: (a) Soloshonok, V. A. In ref.la; pp 229-262. (b) Uneyama, K. In ref. 1a; pp 391-418. (c) Soloshonok, V. A. In ref. 1b; pp 74-83. (c) Abouabdellah, Α.; Bégué, J.-P.; Bonnet-Delpon, D.; Kornilov, Α.; Rodrigues, I.; Nga, T. T. T. In ref. 1b; pp 84-97. (d) Zanda, M.; Bravo, P.; Volonterio, A. In ref. 1b; pp 127-141. (e) Ojima, I.; Inoue, T.; Slaster, J. C ; Lin, S.; Kuduk, S. D.; Chakravarty, S.; Walsh, J. J.; Cresteil, T.; Monsarrat, B.; Pera, P.; Bernacki, R. J. In ref. 1b; pp 158-181. (f) Ojima, I.; Kuznetsova, L., Ungureanu, I. M.; Pepe, A,; Zanardi, I.; Chen, J. In ref. lc; pp 544-561. (g) Qing, F.-L.; Qiu, X. - L . In ref. Id; pp 562-571. (h) Fustero, S.; Sanz-Cervera, J. F.; Piera, J.; Sánchez-Roselló, J. F.; Piera, J.; SánchezRoselló, M.; Jiménez, D.; Chiva, G. In ref. 1c; pp 593-610. For reviews on thel,2-addition to the carbon-nitrogen double bond see: (a) Denmark, S. E.; Nicaise, O. J. -C. J. Chem. Soc, Chem. Commun. 1996,

5.

999-1004. (b) Enders, D,; Reinhold, U. Tetrahedron: Asymmetry 1997, 8, 1895-1946. (c) Bloch, R. Chem. Rev. 1998, 98, 1407-1438. (d) Kobayashi, S.; Ishitani, H. Chem. Rev. 1999, 99, 1069-1094. (e) Merino, P.; Franco, S,; Merchan, F. L.; Tejero, T. Synlett 2000, 442-454. (f) Alvaro, G.; Savoia, D. Synlett 2002, 651-673. For a recent review, see. Job, Α.; Janeck, C. F.; Bettray, W.; Peters, R.; Enders, D. Tetrahedron 2002, 58, 2253-2329.


461 6. 7. 8.

9.


10. 11. 12.

13. 14. 15. 16. 17. 18. 19. 20. 21.

Enders, D.; Funabiki, K . Org. Lett. 2001, 3, 1575-1577. Fries, S.; Pytkowicsz, J.; Brigaud, T. Tetrahedron Lett. 2005, 46, 4761-4764. (a) Bailey, W. F.; Punzalan, E. R. J. Org. Chem. 1990, 55, 5404-5406. (b) Negishi, E.; Swanson, D . R.; Rousset, C. J. J. Org. Chem. 1990, 55, 54065409. Funabiki, K . ; Nagamori, M .; Matsui, M . ; Enders, D . Synthesis 2002, 25852588. Manabe, K . ; Oyamada, H . ; Sugita, K . ; Kobayashi, S. J. Org. Chem. 1999, 64, 8054-8057. For the allylation of fluorine-free aldehyde S A M P - or RAMP-hydrazones see: Enders, D.; Schankat, J.; Klatt, M. Synlett 1994, 795-798. For the pioneering work for Sml -induced cleavage of nitrogen-nitrogen single bond of hydrazines, see: Souppe, J.; Danon, L.; Namy, J. L.; Kagan, H . B. J. Organomet. Chem. 1983, 250, 227-236. Enders, D.; Del Signore, G . Tetrahedron:Asymmetry 2004, 15, 747-751. Enders, D.; Braig, V . ; Boudou, M. Raabe, G . Synthesis 2004, 2980-2990. Ding, H . ; Friestad, G . K . Org. Lett. 2004, 6, 637-640. Funabiki, K . ; Nagamori, M.; Matsui, M . J. Fluorine Chem. 2004, 125, 1347-1350. Ref. 11 and Marshall, J. A . ; Garofalo, A. W.; Sedrani, C. R. Synlett 1992, 643-645. Juaristi, E.; Escalante, J.; Lamatsche, B.; Seebach, D . J. Org. Chem. 1992, 57, 2396-2398. Davis, F. A .; Prasad, K . R.; Nolt, M . B.; Wu, Y . Org. Lett. 2003, 5, 925-927. Davis, S. B.; McKervey, M . A . Tetrahedron Lett. 1999, 40, 1229-1232. Davis, F. A . ; Szewczyk, J. M . Tetrahedron Lett. 1998, 39, 5951-5954. 2


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