N-acyl- and N-sulfonylformamidines from cyanamides and carbodiimides by hydroalumination and subsequent treatment with electrophiles

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DOI: 10.1002/ejoc.201300208

N-Acyl- and N-Sulfonylformamidines from Cyanamides and Carbodiimides by

Hydroalumination and Subsequent Treatment with Electrophiles

Johannes Hellmann,^[a]Ines Rhotert,^[b]Hauke Westenberg,^[b]Roland Fröhlich,^[a]

Birgit Wibbeling,^[a]Werner Uhl,^[b]and Ernst-Ulrich Würthwein*^[a]

Keywords: Acylation / Aluminium / Synthetic methods / Hydrides / Density functional calculations

Hydroalumination of cyanamides 1 with di(isobutyl)alumin-

ium hydride affords intermediate compounds 3, which have

dimeric structures in the solid state with four-membered

R₂AlH (R = tBu, iBu) to give compounds 9 in which one C=N

bond of the carbodiimide is reduced to form an amidinate

ligand and a second molecule of the hydride is coordinated

Al₂N₂heterocycles and exocyclic N=C double bonds. The re- through an Al–N and an Al–H–Al bond. Treatment of 9 with

actions of 3 with acyl chlorides yield NЈ,NЈ-disubstituted N-

acylformamidines 5, whereas reaction with sulfonyl chlorides

give the corresponding N-sulfonylformamidines 7. In con-

trast, carbodiimides 8 react with dialkylaluminium hydrides

acyl chlorides yields N,NЈ-disubstituted N-acylformamidines

10, whereas reaction with sulfonyl chlorides gives the corre-

sponding N-sulfonylformamidines 11.

cyanamide has previously been used in a hydroalumination

reaction, but the product has not been applied in synthe-

sis.^[3]Hydroalumination reactions of carbodiimides seem to

be unknown. In this report we describe the hydroalumi-

nation reactions of cyanamides and carbodiimides followed

by treatment with acylating or sulfonylating agents to syn-

thesise NЈ,NЈ-disubstituted N-acyl-^[4]and N-sulfonylform-

amidines^[5]and the respective N,NЈ-disubstituted NЈ-acyl^[6]

and NЈ-sulfonyl^[7]derivatives. These classes of compounds

have found considerable use in the synthesis of organic

heterocycles and in pharmacological studies.^[8]N-Acyl-

amidines are widely applicable as ligands for metal com-

plexation.^[9]

N-Substituted formamidines, e.g., acyl formamidines and

sulfonyl formamidines, are usually synthesised by the reac-

tion of amides with N,N-dimethylformamide diethyl

acetal.^[10]Due to the high importance of such compounds,

new procedures for the synthesis were developed recently. Li

et al. obtained N-sulfonyl formamidines unexpectedly from

tertiary amines and sulfonyl azide in the presence of diethyl

azodicarboxylate (DEAD) as dehydrogenation reagent.^[11]

Wang et al. reported a similar FeCl₃-mediated pathway to

N-sulfonyl formamidines starting from triethylamine and

sulfonyl azide.^[12]

Introduction

The Pauling electronegativities, as revised by Allred and

Rochow, of aluminium and carbon or nitrogen differ by

1.03 and 1.60 units, respectively, thus indicating a substan-

tial ionic character of the respective bonds.^[1]Consequently,

aluminium–carbon and aluminium–nitrogen compounds

exhibit a pronounced nucleophilic character at carbon or

nitrogen. Furthermore, considering the high Lewis acidity

of aluminium, which may significantly influence reactivity

and stereoselectivity, its compounds seem to offer valuable

synthetic advantages. Interestingly, these two valuable and

cooperative properties have not yet been fully explored in

organic synthesis. Many intermediate aluminium com-

pounds are simply hydrolyzed, introducing a proton as elec-

trophile, e.g., in the hydrolytic workup of hydroalumination

products in reductions with di(isobutyl)aluminium hydride

(DIBAL-H). But hydroalumination is a facile procedure

that can be used to generate organoaluminium derivatives

from unsaturated organic substrates such as alkynes, to a

lesser extent alkenes, and nitrogen-containing double and

triple bonds.^[2]To the best of our knowledge, only dimethyl-

[a] Organisch-Chemisches Institut, Westfälische Wilhelms-

Universität,

There is considerable interest in the synthesis and proper-

ties of unsaturated nitrogen-containing compounds, in par-

ticular of N-substituted formamidines starting from cyan-

amides and carbodiimides. In a first step we reduced the

cyanamides and carbodiimides with DIBAL-H to yield the

corresponding aluminium formamidinates. These interme-

diates show high reactivity towards electrophiles such as

carboxylic and sulfonic acid chlorides.

Corrensstrasse 40, 48149 Münster, Germany

Fax: +49-251-83-39772

E-mail: wurthwe@uni-muenster.de

Homepage: http://ww w .uni-muenster.de/Chemie/OC/research/

wue/euw.htm

[b] Institut für Anorganische und Analytische Chemie,

Westfälische Wilhelms-Universität,

Corrensstrasse 30, 48149 Münster, Germany

Supporting information for this article is available on the

WWW under http://dx.doi.org/10.1002/ejoc.201300208.

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Results and Discussion

Cyanamides

In a first step, cyanamides 1 were treated in anhydrous

toluene with DIBAL-H to obtain the corresponding di-

meric aluminium formamidinates 3a and 3b by reduction

of the CϵN triple bonds (Scheme 1). Both aluminium com-

pounds were fully characterised, including by X-ray crys-

tallography (Figure 1). They have centrosymmetric dimeric

formula units in the solid state, with four-membered Al₂N₂

heterocycles and the former nitrile nitrogen atoms in the

bridging positions. The amino groups are in anti positions.

These results are in accordance with reports of Zakharkin

and Khorlina,^[13]Wade et al.,^[14]Haley et al.^[15]and Uhl et

al.^[16]on the hydroalumination of simple nitriles. The Al–N

distances range from 1.909(1) to 1.926(1) Å, which is inter-

mediate between typical covalent (ca. 1.8 Å) and dative Al–

N bonds (ca. 2.0 Å).^[17]The transannular Al–Al separations

are 2.836 (av.) and 2.827 (av.) Å for 3a and 3b, respectively.

The exocyclic C=N bond lengths are close to standard val-

ues [1.281(2) to 1.288(2) Å]. No Al–O interaction was ob-

served in compound 3b, in spite of the well-known oxophil-

icity of aluminium.^[18]

Figure 1. Molecular structures of 3a (top) and 3b (bottom) in the

solid state.

Scheme 1. Hydroalumination of cyanamides 1a and 1b.

The dimerisation of the coordinatively unsaturated up was necessary. The crude reaction mixture was directly

monomers 2a and 2b to form the observed dimeric struc- subjected to column chromatography over silica gel, en-

tures 3a and 3b is highly exothermic, as gas-phase quantum abling transformation into the ultimately isolated, alumin-

chemical calculations indicate. The geometries of the mono- ium-free products, probably by hydrolysis on the wet, polar

mer 2b and the dimer 3b were completely optimised at the silica gel. After optimisation of the reaction conditions it

DFT-level B3LYP/6-311+G(d,p)//B3LYP/6-311+G(d,p).^[19]was found that the best cyanamide/DIBAL-H/electrophile

Relative energies were also obtained from SCS-MP2-single ratio of reagents was 1:1:1.2, which led to moderate to good

point calculations^[20]and by correcting the DFT-energies isolated yields. Toluene proved to be the best solvent. Aro-

using the D3-method,^[21]which takes dispersion energy into matic acid chlorides gave better yields because the reaction

account. The dimerisation energy for 2b was calculated to products were easier to separate from the aluminium side

be –45.8 kcal/mol at the DFT-level [SCS-MP2-level: products. Cyclic or acyclic cyanamides behaved similarly in

–71.2 kcal/mol; D3-B3LYP/6-311+G(d,p): –68.0 kcal/mol] these reactions.

(all include zero point energy).

Compounds 5c and 5f were characterised by single-crys-

For synthetic application, it was not necessary to isolate tal X-ray diffraction analysis (Figure 2). Both structures

the intermediate aluminium compounds 3. The reaction of show E-configuration of the C=N bond and a sickle-type

symmetrically disubstituted cyanamides 1 with DIBAL-H arrangement of the almost planar central O=C–N=C(H)–

in anhydrous toluene and subsequent quenching with vari- N(R₂) chain with dihedral angles for the O=C–N=C unit

ous carboxylic acid chlorides 4 yielded N-acyl-NЈ,NЈ-disub- of 17.4(2)° (5c) vs. 11.8(2)° (5f) and –168.2(2)° (5c) vs.

stituted formamidines 5. Treatment with sulfonic acid –171.0(1)° (5f) for the C–N=C–N unit. The bond lengths

chlorides 6 generated the related N-sulfonyl formamidines along the O=C–N=CH–N chain are 1.224(2), 1.365(2),

7 (Scheme 2 and Table 1). In all cases, no hydrolytic work- 1.299(2) and 1.313(2) Å for 5c, and 1.233(2), 1.373(2),

2

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Synthesis of N-Acyl- and N-Sulfonylformamidines

bonds of the amidine (N–C–N) subunit have the same

length [1.307(2) Å], again indicating the importance of elec-

tron delocalisation in this part of the molecule.

Figure 3. Molecular structures of compound 7b in the solid state.

Scheme 2. Synthesis of N-acyl- 5 and N-sulfonylformamidines 7

from cyanamides 1.

Reaction Mechanism

To investigate the mechanism of the acylation of mono-

mer 2 and dimer 3 in more detail, gas-phase quantum

chemical calculations were performed. The geometries of

the relevant species A–H were completely optimised at the

DFT-Level B3LYP/6-311+G(d,p)//B3LYP/6-311+G(d,p).

Relative energies were also obtained from SCS-MP2-single

point calculations^[20]and by correcting the DFT-energies

using the D3-method,^[21]which considers dispersion energy.

The following relative energies contain zero point correc-

tions.

At first, calculations were performed to investigate the

reaction of acetyl chloride with the monomeric product

(such as 2) resulting from the hydroalumination of the

model compound N,N-dimethylcyanamide with di(tert-but-

yl)aluminium hydride (Figure 4). The hydroaluminated

species forms a van der Waals complex A (E_rel= 0.0 kcal/

mol) with acetyl chloride. Starting from this complex, two

different reaction pathways were investigated. One leads to

a four-membered transition state B, in which the chlorine

atom interacts with the aluminium atom and the carbonyl

Table 1. Substitution patterns and isolated yields of compounds

5a–j, 7a and 7b.

Product

NR₂

R¹

Yield [%]

5a

5b

5c

5d

5e

5f

5g

5h

5i

NEt₂

NiPr₂

Ph

76

86

81

87

30

60

81

30

70

68

81

64

4-Me-C₆H₄

Ph

4-Me-C₆H₄

tBu

NiPr₂

pyrrolidinyl

morpholinyl

NiPr₂

Ph

4-Me-C₆H₄

tBu

Ph

4-Me-C₆H₄

Ph

4-Me-C₆H₄

5j

7a

7b

NiPr₂

1.317(2) and 1.311(2) Å for 5f, indicating the dominating

resonance interaction along the conjugated hetero sys-

tem.^[9j,9l]

carbon atom approaches the iminic nitrogen atom [E_rel

=

–1.6 (DFT), –1.6 (SCS-MP2), –1.7 (D3) kcal/mol with re-

spect to van der Waals complex A]. The relevant atomic

distances being C–Cl 2.167 Å; C–N 2.670 Å, N–Al 1.955 Å;

Al–Cl 2.625 Å. The second pathway involves an approach

of the carbonyl oxygen atom towards the aluminium centre,

forming an intermediate complex C with an O–Al–distance

of 2.075 Å [E_rel= –6.1 (DFT), –6.1 (SCS-MP2), and –5.3

(D3) kcal/mol]. The next reaction step leads from C to a

four-membered transition state D [E_rel= 1.1 (DFT), 1.0

(SCS-MP2), –1.3 (D3) kcal/mol], which is characterised by

a relative long carbon–nitrogen distance of 2.309 Å and a

significant coordinative oxygen–aluminium interaction

(1.996 Å). From both transition states B and D, in very exo-

thermic steps, the final product E {–38.4 [DFT, –47.5 (SCS-

MP2), –43.4 (D3) kcal/mol]} with the new carbon–nitrogen

bond is formed, whereas the chlorine atom is bound to alu-

Figure 2. Molecular structures of compounds 5c (top) and 5f (bot-

tom) in the solid state.

The molecular structure of 7b (Figure 3) is also charac- minium with bond lengths of Al–Cl: 2.197 Å, C–N:

terised by an almost planar O–S–N=C–N chain [torsion 1.438 Å; N–Al: 2.089 Å. In summary, both reaction path-

angles 8.1(2)°, –179.4(2)°] with an E-configuration across ways involve cyclic four-membered transition states. The

the C=N bond. The lengths of the S–O bonds are 1.422(1) geometrical and energetic parameters of the transition

and 1.437(1) Å, the S–N distance is 1.610(2) Å. Both N–C states strongly underline the cooperative character of this

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bond-forming step, indicated by substantial Al–O or Al–Cl

interactions in the first part of the mutual approach of both

reaction partners.

Figure 4. Van der Waals complex A, transition B, complex C, tran-

sition state D and final product E [kcal/mol; SCS-MP2/B3LYP/6-

311+G(d,p)//B3LYP/6-311+G(d,p) + zero point correction].

Secondly, the acylation of dimer 3b was also studied

computationally (Figure 5). With regard to the huge dimer-

isation energy of 2, we assume that this pathway gives a

more realistic view of the reactions studied experimentally

compared with the monomer reaction described above.

Once more a weakly bound van der Waals complex F was

identified (E_rel= 0.0 kcal/mol). The approach of the carb-

onyl carbon atom of acetyl chloride to the respective nitro-

gen atom leads to a well-defined energy-rich transition state

G [C–N: 1.970 Å; 44.7 (DFT), 36.5 (SCS-MP2), 31.1 (D3)

kcal/mol with respect to F]. Because both aluminium atoms

are already four-coordinate, no interaction of chloride to

one of the two aluminium atoms can take place (Al–Cl:

3.295 Å). This transition state leads to the intermediate ad-

dition product H, resulting from bond formation between

nitrogen and carbon; it is characterised by an Al–N–Al

chain originating from the former A-N–Al–N four-mem-

bered ring. One of the two four-coordinate Al atoms carries

the acylated amidine, the other has the chloride ion bound.

This intermediate product H is lower in energy compared

with the van der Waals complex F {–2.7 [DFT, –12.2 (SCS-

MP2), –12.0 kcal/mol]}. We assume that this intermediate

is then subject to a second acylation, leading finally by

dissociation to two products of type E (see above) in a very

exothermic reaction {–26.4 [DFT, –27.4 (SCS-MP2), –28.4

(D3) kcal/mol]}. Here again, the transition state and the

products benefit from the cooperative properties of Al and

N, respectively.

Figure 5. Van der Waals complex F, transition state G, and interme-

diate acylation product [kcal/mol; SCS-MP2/B3LYP/6-

311+G(d,p)//B3LYP/6-311+G(d,p) + zero point correction].

H

Reactions with Carbodiimides

Similarly to the hydroalumination of cyanamides 1, we

investigated the reduction of carbodiimides 8 by dialkyl-

aluminium hydrides. Reaction of N,NЈ-diphenylcarbodi-

imide (8c) with di(tert-butyl)aluminium hydride in a molar

ration of 1:1 afforded only small quantities of the hydro-

alumination product 9c. However, with a 1:2 ratio the yield

was enhanced to 35%. Further compounds of unknown

constitution were formed as by-products (Scheme 3).

Scheme 3. Hydroalumination of carboddimide 8c.

4

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Synthesis of N-Acyl- and N-Sulfonylformamidines

The structure of 9c may be described by single hydro-

alumination of 8c, followed by the formation of an adduct

with a second equivalent of the aluminium reagent forming

the six-membered heterocycle of 9c with a hydride bridge

between both aluminium atoms.^[22]Compound 9c was fully

characterised by NMR spectroscopic analysis and shows

resonances of phenyl and tert-butyl groups in a molar inten-

sity ratio of 1:2. The signal for the bridging hydride ion is

observed at δ = 3.32 ppm, which is typical of aluminium

hydrides. The CH group between the nitrogen atoms gave

resonances at δ = 168.9 ppm (¹³C NMR) and 7.43 ppm (¹H

NMR). Boese et al. obtained the corresponding boron com-

pounds by hydroboration of carbodiimides.^[23]

Single crystals of 9c were obtained from a solution in n-

hexane at 2 °C. The compound crystallised in the centro-

symmetric space group P1 with two independent molecules

Scheme 4. Formation of N,NЈ-disubstituted N-acyl- 10 and N-sulf-

onylformamidines 11 from carbodiimides

hydroalumination products 9.

¯

8 via intermediate

per asymmetric unit (Figure 6 and the Supporting Infor-

mation). The six-membered Al₂N₂CH rings in the molecu-

lar centres adopt a twist form in the solid state. The dihe-

dral angles for the endocyclic groups Al–N–C–N vary be-

tween 18.8(3) and 23.7(3)°, those for the C–N–Al–H moie-

ties between 34.3 and 36.0°, and those for Al–H–Al–N

groups between 8.9 and 16.5°. The C–N bonds in the six-

membered ring exhibit lengths of 1.318(3) (C1–N1) to

1.329(3) Å (C1–N2), which is characteristic of delocalised

N–C–N π-systems as in amidines. The Al–N distances

[1.951(2) to 1.956(2) Å] as well as the Al–H distances

[1.70(2) to 1.72(2) Å] reflect the symmetrical structure of

the molecules with two almost identical molecular halves.

The sum of the angles at the nitrogen atoms is always close

to 360° [358.8 (N4) to 359.6° (N3)] and verifies the almost

ideal planar coordination sphere with the π-conjugation ac-

ross the bonds of the N3–C1–N15 group.

Table 2. Substitution patterns and isolated yields of compounds

10a–f and 11a–c.

Product

R¹

R²

R³

Yield [%]

10a

10b

10c

10d

10e

10f

11a

11b

11c

Ph

iPr

75

44

98

62

50

15

72

73

47

4-Me-C₆H₄iPr

Ph

4-Me-C₆H₄Et

tBu Et

4-Me-C₆H₄iPr

4-Me-C₆H₄cyclohexyl cyclohexyl

4-Me-C₆H₄Et tBu

cyclohexyl cyclohexyl

Ph

tBu

iPr

By employing an unsymmetrical carbodiimide, N-ethyl-

NЈ-tert-butylcarbodiimide (8d), in this reaction sequence,

the best yield of the products 10e, 10f and 11c was 50 %.

Upon reaction with acid or sulfonyl chlorides we could iso-

late in each case only one of the two possible isomers

(Table 2). Their constitutions were established by NMR

spectroscopic analysis, EI mass spectrometry and, in the

case of 11c, by X-ray diffraction.

The N-acylated compounds 10c and 10d were character-

ised by X-ray crystal structure determination. They differ

in the orientation of the central O=C–N–C(H)=N chain,

possibly due to the differing substituents (cyclohexyl vs.

phenyl) or because of packing effects (Figure 7). Com-

pound 10c shows

–162.0(2)°], whereas 10d shows a W-type configuration

a sickle-type structure [166.8(2)°,

Figure 6. Molecular structure of 9c in the solid state.

[–0.1(2)°, –168.0(1)°]. In comparison to the electronically

As in the case of hydroaluminated cyanamides 3, the re- delocalised NЈ,NЈ-disubstituted N-acyl- and N-sulfonyl-

action of the aluminium intermediates 9 with organic elec- formamidines 5 and 7, the molecules 10c and 10d have iso-

trophiles did not require their isolation. Thus, carbodi- lated, relatively long C–N single bonds [10c: 1.401(2) Å,

imides 8 were first treated with DIBAL-H and then 10d: 1.381(2) Å] and short C=N double bonds [10c and 10d:

quenched with acid chlorides to give access to N-acyl-N,NЈ- 1.256(2) Å]. These differing structural properties underline

disubstituted formamidines 10, whereas the reactions with nicely the electronic influence of a two-coordinate amidine

sulfonic acid chlorides 6 yielded the related N-sulfonyl nitrogen atom bound to the C=O or SO₂group, respec-

formamidines 11 (Scheme 4, Table 2). In accordance with tively, as found in 5c, 5f and 7b on the one hand (N-acyl-

the molecular structure of 9, optimum yields were obtained imine-type), compared with a three-coordinate central

by using two equivalents of DIBAL-H and 2.4 equivalents amidine nitrogen atom as found in 10c and 10d (amide-

of the respective electrophile.

type) on the other hand.

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ing materials were first transformed into reactive alumin-

ium compounds 3 and 9, which were then treated with elec-

trophiles such as acid or sulfonyl chlorides to yield, after

work up on silica gel, a range of substituted N-acyl- and N-

sulfonylformamidines 5, 7, 10 or 11 in satisfactory yield.

The optimised reaction conditions do not involve a special

hydrolytic workup step, and direct chromatographic separa-

tion was found to be superior for the isolation of the final

products. The structures of several products in the solid

state could be elucidated by X-ray crystallography, includ-

ing the quite reactive hydroalumination intermediates 3 and

9. This work should encourage organic chemists to use such

aluminium compounds systematically as reactive intermedi-

ates for ambitious organic syntheses in place of the better

known lithium or magnesium compounds.

Figure 7. Molecular structures of 10c and 10d in the solid state.

Experimental Section

General: Melting points are uncorrected. ¹H, ¹³C, GCOSY,

The X-ray structures of 11b and 11c show – in spite of

their different substitution pattern – similarities, with re-

spect to both dihedral angles and bond lengths of the cen-

tral SO₂–NR–CH=NR subunit (Figure 8). The group O–S–

GHSQC and GHMBC spectroscopy used TMS (¹H) (δ

=

0.00 ppm), CD₂Cl₂(¹H: 5.32 ppm, ¹³C: 54.00 ppm), CDCl₃(¹³C:

77.16 ppm) or C₆D₆(¹H: 7.16 ppm, ¹³C: 128.06 ppm) as internal

references. When necessary, the experiments were carried out with

N–C–N of 11b is characterised by dihedral angles of complete exclusion of moisture. Compound 8c was prepared ac-

cording to the literature.^[24]

–145.4(2) and 179.6(2)°, and that of 11c of 151.1(3) and

172.5(3)°, highlighting the relatively flat W-type configura-

[iBu₂Al-N=CH-NC₄H₈]₂(3a): 1-Cyanopyrrolidine (1a; 192 mg,

tion. As in compounds 10c and 10d, the C–N bond lengths 2.0 mmol) was dissolved in toluene (20 mL; dried with Na/benzo-

phenone) and treated with DIBAL-H (2; 0.36 mL, 2.0 mmol) at

room temperature under argon. After stirring for 2 h, the solution

was concentrated and cooled to 4 °C to yield colourless crystals

of 3a. Yield 386 mg (0.81 mmol, 81%), m.p. 122 °C (argon, closed

capillary). ¹H NMR (C₆D₆, 400 MHz): δ = 0.47 (d, ³J_H,H= 6.7 Hz,

differ significantly [C–N: 1.399(3) Å in 11b, 1.405(5) Å in

11c; C=N: 1.258(3) Å in 11b and 1.257(5) Å in 11c] indicat-

ing again the completely different electronic structure com-

pared with the NЈ,NЈ-disubstituted N-sulfonylformamidines

7.

8 H, AlCH₂CHMe₂), 1.09 and 1.27 (each br, 4 H, NCH₂CH₂), 1.32

3

(d, J_H,H

= 6.4 Hz, 24 H, AlCH₂CHMe₂), 2.25 (m, 4 H,

AlCH₂CHMe₂), 2.66 (very br., 4 H, NCH₂), 3.46 (br., 4 H, NCH₂),

7.66 (s, 2 H, HC=N) ppm. ¹³C{¹H} NMR (C₆D₆, 100 MHz): δ =

24.6 (NCH₂CH₂), 26.5 (AlCH₂CHMe₂), 27.2 (AlCH₂CHMe₂),

29.1 (AlCH₂CHMe₂), 44.7 and 48.5 (NCH₂), 154.4 (C=N) ppm.

IR (paraffin, CsI plates): ν = 1991 (m), 1956 (w), 1842 (m, br),

˜

1694 (sh), 1639 (sh), 1611 (sh), 1578 [vs. ν(C=N)], 1460 [vs. (paraf-

fin)], 1402 [m δ(CH₃)], 1375 [s (paraffin)], 1356 (sh), 1335 (m), 1310

(m), 1246 (m), 1223 [s δ(CH₃)], 1167 (s), 1113 (m), 1059 (s), 1031

(m), 1009 (s), 970 (m), 945 (s), 930 (m), 914 (m), 872 (s), 814 (vs),

747 [s ν(CC), ν(CN)], 727 [s (paraffin)], 671 (m), 656 (sh), 627 (w),

602 (w), 588 (w), 542 (m), 494 (w), 457 [s δ(CC), ν(AlC),

ν(AlN)] cm^–1. MS (EI, 20 eV, 100 °C): m/z (%)

= 475 (1)

[M(dimer)⁺– H], 419 (100) [M⁺– CH₂CHMe₂], 363 (65) [M⁺

CH₂CHMe₂– butene], 307 (44) [M⁺– CH₂CHMe₂– 2butene].

–

X-ray Crystal Structure Analysis of 3a:^[25]C₂₆H₅₄Al₂N₄; M =

476.69; colourless crystal; 0.24ϫ0.11ϫ0.10 mm; a = 10.5376(2), b

= 11.6532(2), c = 13.3681(2) Å, α = 78.701(1)°, β = 72.876(1)°, γ =

79.582(1)°; V = 1525.04(5) Å³; ρ_calc= 1.038 gcm^–3; μ = 0.984 mm^–1;

empirical absorption correction (0.798 Յ T Յ 0.908); Z = 2; tri-

Figure 8. Molecular structures of 11b (above) and 11c (below) in

the solid state.

¯

clinic; space group P1 (No. 2); λ = 1.54178 Å; T = 153(2) K; ω and

φ scans, 8720 reflections collected (Ϯh, Ϯk, Ϯl), [(sinθ)/λ] =

0.60 Å^–1, 4861 independent (R_int= 0.0197) and 4180 observed re-

Conclusions

flections [IϾ2σ(I)], 297 refined parameters, R = 0.0428, wR²

=

We have demonstrated the enormous synthetic potential 0.1238, max. (min.) residual electron density 0.499 (–0.235)eÅ^–3,

hydrogen atoms calculated and refined as riding atoms.

of hydroalumination reactions of unsaturated nitrogen com-

pounds such as cyanamides 1 and carbodiimides 8. In a

[iBu₂Al-N=CH-NC₄H₈O]₂(3b): A solution of 4-morpholinecarbo-

simple one-pot procedure the commercially available start- nitrile (3b; 224 mg, 2 mmol) in toluene (20 mL; dried with Na/

6

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Synthesis of N-Acyl- and N-Sulfonylformamidines

benzophenone) was treated with a solution of DIBAL-H (2;

2 mmol, 1.0 m in toluene, 2 mL) at room temperature under argon.

The mixture was stirred for 16 h and concentrated. Cooling of the

solution to –30 °C yielded colourless crystals of 3b. Yield 260 mg

ylbenzoyl chloride (0.371 g, 2.4 mmol) according to the general

procedure. Subsequent column chromatography (diethyl ether/n-

pentane, 2:1 + 10% triethylamine) and HPLC (ethyl acetate/cyclo-

hexane, 1:2) gave the pure product (0.376 g, 1.70 mmol, 86%) as a

(0.51 mmol, 51%), m.p. 169 °C (argon, closed capillary). ¹H NMR colourless solid (m.p. 46–47 °C). ¹H NMR (300 MHz, CDCl₃): δ =

3

(C₆D₆, 400 MHz):

δ

=

0.34 (d, J_H,H

=

6.4 Hz,

8

H, 1.27 (t, ³J = 7.2 Hz, 3 H, CH₃), 1.27 (t, J = 7.2 Hz, 3 H, CH₃),

3

AlCH₂CHMe₂), 1.23 (d, J_H,H= 6.7 Hz, 24 H, AlCH₂CHMe₂), 2.40 (s, 3 H, Ar-CH), 3.44 (q, J_H,H= 7.2 Hz, 2 H, CH₂), 3.67 (q,

2.10 (m, 4 H, AlCH₂CHMe₂), 2.90 (br., 8 H, NCH₂), 3.18 (s, 4 H, ³J_H,H= 7.2 Hz, 2 H, CH₂), 7.23 (d, J = 7.9 Hz, 2 H, m-CH_Ar), 8.14

3

OCH₂), 7.22 (s,

2

H, HC=N) ppm. ¹³C{¹H} NMR (C₆D₆,

(d, J_H,H= 8.1 Hz, 2 H, o-CH_Ar), 8.63 (s, 1 H, NCH) ppm. ¹³C

100 MHz): δ = 25.2 (AlCH₂CHMe₂), 27.0 (AlCH₂CHMe₂), 28.9 NMR (75 MHz, CDCl₃): δ = 12.7, 15.0 (NCH₂CH₃), 21.8, 41.3

(AlCH₂CHMe₂), 46.1 (br., NCH₂), 66.5 (OCH₂), 155.4 (NCH₂), 47.5 (p-CCH₃), 129.1, 130.2 (CH_Ar), 135.1 (C_q), 142.7 (p-

(C=N) ppm. IR (paraffin, CsI plates): ν = 1969 (m), 1934 (w), 1915 CCH ), 160.0 (NCN), 177.7 (CO) ppm. IR (neat): ν = 3026 (vw),

˜

3

(w), 1883 (vw), 1838 (w), 1794 (w), 1603 (s, br), 1585 (s), 1575 [s 2976 (w), 2936 (w), 2874 (w), 1638 (s), 1609 (m), 1580 (vs), 1564

ν(C=N)], 1543 (m), 1466 (m), 1371 [m (paraffin)], 1312 (w), 1263 (vs), 1506 (w), 1449 (s), 1381 (m), 1337 (vs), 1306 (s), 1250 (vs),

(w), 1231 [m δ(CH₃)], 1169 (m), 1109 (m), 1067 (m), 1003 (w), 978 1206 (m), 1169 (m), 1134 (m), 1078 (s), 1069 (s), 999 (m), 941 (w),

(w), 941 (m), 862 (s), 818 [s ν(CC), ν(CN)], 729 [s (paraffin)], 538

885 (w), 845 (w), 812 (w), 789 (w), 760 (s), 692 (w), 648 (m), 606

(w), 440 [m δ(CC), ν(AlC), ν(AlN)] cm^–1. MS (EI, 20 eV, 50 °C):

(s), 530 (w) cm^–1. HRMS (ESI): m/z calcd. for C₁₃H₁₈N₂O⁺

m/z (%) = 507 (0.2) [M⁺], 451 (100) [M⁺– CH₂CMe₃], 395 (85) 219.1492; found 219.1498. C₁₃H₁₈N₂O (218.30): calcd. C 71.53, H

[M⁺– CH₂CHMe₂– butene], 339 (48) [M⁺– CH₂CHMe₂– 2 but-

ene].

8.31, N 12.83; found C 71.83, H 8.27, N 12.66.

N-[(Diisopropylamino)methylene]benzamide(5c):^[26]Obtained from

N,N-diisopropylcyanamide (1d; 0.252 g, 2 mmol) and benzoyl

chloride (0.337 g, 0.24 mmol) according to the general procedure.

Pure product 5c (0.376 g, 1.62 mmol, 77%) was obtained by col-

umn chromatography (diethyl ether/n-pentane, 1:1 + 10% triethyl-

amine) and HPLC (ethyl acetate/cyclohexane, 1:1) as a colourless

solid (m.p. 104 °C). ¹H NMR (600 MHz, CD₂Cl₂): δ = 1.37 [d,

X-ray Crystal Structure Analysis of 3b:^[25]C₂₆H₅₄Al₂N₄O₂; M =

508.69; colourless crystals; 0.73ϫ0.30ϫ0.24 mm; a = 15.6654(3),

b

= 18.6875(4), c = 17.6834(4) Å, β = 112.727(1)°; V =

4774.8(2) Å³; ρ_calc= 1.061 gcm^–3; μ = 1.019 mm^–1; empirical ab-

sorption correction (0.523 Յ T Յ 0.792); Z = 6; monoclinic; space

group P2₁/c (No. 14); λ = 1.54178 Å; T = 153(2) K; ω and φ scans,

27654 reflections collected (Ϯh, Ϯk, Ϯl), [(sinθ)/λ] = 0.60 Å^–1, 8824

independent (R_int= 0.030) and 7388 observed reflections [IϾ2σ(I)],

550 refined parameters, R = 0.0478, wR²= 0.1432, max. (min.)

residual electron density 0.432 (–0.311)eÅ^–3, hydrogen atoms cal-

culated and refined as riding atoms.

3

³J_H,H= 7.0 Hz, 6 H, NCH(CH₃)₂], 1.38 [d, J_H,H= 7.1 Hz, 6 H,

3

NCH(CH₃)₂], 3.76 [hept, J_H,H= 6.8 Hz, 1 H, NCH(CH₃)₂], 4.77

3

[hept, J_H,H= 6.8 Hz, 1 H, NCH(CH₃)₂], 7.40–7.43 (m, 2 H, m-

CH_Ar), 7.47–7.51 (m, 1 H, p-CH_Ar), 8.23–8.25 (m, 2 H, o-CH_Ar),

8.79 (s, 1 H, NCHN) ppm. ¹³C NMR (150 MHz, CD₂Cl₂): δ =

20.2, 23.8 [NCH(CH₃)₂], 48.3 [NCH(CH₃)₂], 49.8 [br.,

NCH(CH₃)₂], 128.4 (m-CH_Ar), 130.1 (o-CH_Ar), 132.0 (p-CH_Ar),

General Procedure for the Formation of NЈ,NЈ-Disubstituted N-

Acylformamidines 5 and N-Sulfonylformamidines 7: Cyanamide 1

(1 equiv.) was dissolved in toluene (5 mL per mmol) and DIBAL-

H (1 m in toluene, 1 equiv.) was added. After stirring the reaction

mixture for 30 min, the electrophile (1.2 equiv.) was added under

ice-cooling and stirring was continued for at least 2 h. The solvent

was removed under reduced pressure, then the crude product was

purified by column chromatography and – if necessary – by HPLC

and/or recrystallisation from the eluent.

138.0 (i-C_Ar), 158.7 (NCN), 177.6 (CO) ppm. IR (neat): ν = 3065

˜

(s), 3028 (s), 2974 (s), 2930 (s), 2874 (s, CH₃), 2361 (s), 2336 (s),

1626 (s), 1582 (s), 1555 (s), 1452 (s), 1385 (s), 1342 (s), 1319 (s),

1304 (s), 1246 (s), 1198 (s), 1155 (s), 1111 (s), 1065 (s), 1026 (s),

1003 (s), 935 (s), 918 (s), 881 (s), 851 (s), 810 (s), 712 (s), 689 (s),

664 (s), 561 (s) cm^–1. HRMS (ESI): m/z calcd. for C₁₄H₂₁N₂O⁺

233.1647; found 233.1648. C₁₄H₂₀N₂O (232.32): calcd. C 72.38, H

8.68, N 12.06; found C 72.14, H 8.55, N 11.95.

N-[(Diethylamino)methylene]benzamide (5a): Obtained from N,N-

diethylcyanamide (1c; 0.196 g, 2 mmol) and benzoyl chloride

(0.337 g, 2.4 mmol), according to the general procedure. Subse-

quent column chromatography (diethyl ether/n-pentane, 3:1 + 10%

triethylamine) and HPLC (ethyl acetate/cyclohexane, 1:2) gave the

pure product (0.310 g, 1.52 mmol, 76%) as a colourless solid (m.p.

X-ray Crystal Structure Analysis of 5c:^[25]C₁₄H₂₀N₂O; M = 232.32;

colourless crystal; 0.35ϫ0.20ϫ0.10 mm; a = 11.6872(1), b =

9.9337(1), c = 12.0573(1) Å, β = 110.842(1)°; V = 1308.22(2) Å³;

ρ_calc= 1.180 gcm^–3; μ = 0.588 mm^–1; empirical absorption correc-

tion (0.820 Յ T Յ 0.943); Z = 4; monoclinic; space group P2₁/c

(No. 14); λ = 1.54178 Å; T = 223(2) K; ω and φ scans, 8653 reflec-

tions collected (Ϯh, Ϯk, Ϯl), [(sinθ)/λ] = 0.60 Å^–1, 2354 indepen-

dent (R_int= 0.043) and 2104 observed reflections [IϾ2σ(I)], 159

refined parameters, R = 0.041, wR²= 0.106, max. (min.) residual

electron density 0.13 (–0.11)eÅ^–3, hydrogen atoms calculated and

refined as riding atoms.

3

48 °C). ¹H NMR (300 MHz, CD₂Cl₂): δ = 1.27 (d, J_H,H= 7.2 Hz,

3

3 H, CH₃), 1.29 (d, J_H,H= 7.2 Hz, 3 H, CH₃), 3.44 (q, J_H,H

=

3

7.2 Hz, NCH₂), 3.68 (q, J_H,H= 7.2 Hz, 2 H, NCH₂), 7.22–7.70

(m, 3 H, CH_Ar), 8.11–8.45 (m, 2 H, CH_Ar), 8.64 (s, 1 H, CH) ppm.

¹³C NMR (75 MHz, CD₂Cl₂): δ = = 12.7, 15.0 (CH₃), 41.4, 47.5

(NCH₂), 128.4 (p-CH_Ar), 130.1 (o-CH_Ar), 132.1 (m-CH_Ar), 137.8

(C ), 160.0 (NCN), 177.8 (CO) ppm. IR (neat): ν = 3080 (vw), 3061

˜

q

N-[(Diisopropylamino)methylene]-4-methylbenzamide (5d): Ob-

tained from N,N-diisopropylcyanamide (1d; 0.252 g, 2 mmol) and

4-methylbenzoyl chloride (0.371 g, 0.24 mmol) according to the ge-

neral procedure. Pure product 5d (0.430 g, 1.75 mmol, 87%) was

obtained by column chromatography (diethyl ether/n-pentane, 1:1

+ 10% triethylamine) and HPLC (ethyl acetate/cyclohexane, 2:1)

(vw), 2980 (w), 2970 (m), 2936 (w), 2872 (vw), 1634 (vs), 1584 (s),

1568 (s), 1487 (w), 1450 (s), 1439 (s), 1354 (s), 1337 (vs), 1310 (s),

1252 (s), 1207 (s), 1173 (m), 1136 (s), 1105 (s), 1092 (s), 1063 (s),

1024 (m), 1015 (m), 1001 (m), 939 (m), 883 (w), 808 (w), 789 (w),

714 (vs), 691 (m). 667 (s) cm^–1. HRMS (ESI): m/z calcd. for

C₁₂H₁₇N₂O⁺205.1335; found 205.1339. C₁₂H₁₆N₂O (204.27):

calcd. C 70.56, H 7.90, N 13.71; found C 70.44, H 7.91, N 13.58.

1

as a colourless solid (m.p. 74 °C). H NMR (300 MHz, CD₂Cl₂): δ

3

= 1.35 (d, J_H,H= 6.8 Hz, 5 H), 1.37 [d, J_H,H= 6.9 Hz, 6 H,

3

N-[(Diethylamino)methylene]-4-methylbenzamide (5b): Obtained

from N,N-diethylcyanamide (1c; 0.196 g, 2 mmol) and 4-meth-

NCH(CH₃)₂], 2.40 (s, 3 H, Aryl-CH₃), 3.75 [hept, J_H,H= 6.8 Hz,

1 H, NCH(CH₃)₂], 4.76 [hept, J_H,H= 6.8 Hz, 1 H, NCH(CH₃)₂],

3

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E.-U. Würthwein et al.

FULL PAPER

7.22 (d, J_H,H= 8.5 Hz, 2 H, m-CH_Ar), 8.12 (d, J_HH= 8.2 Hz, 2 tions collected (Ϯh, Ϯk, Ϯl), [(sinθ)/λ] = 0.60 Å^–1, 1852 indepen-

H, o-CH_Ar), 8.77 (s, 1 H, NCHN) ppm. ¹³C NMR (75 MHz, dent (R_int= 0.034) and 1668 observed reflections [IϾ2σ(I)], 136

CD₂Cl₂): δ = 20.2, 23.9 [NCH(CH₃)₂], 48.3 f, 49.7 [NCH(CH₃)₂], refined parameters, R = 0.038, wR²= 0.101, max. (min.) residual

3

129.1 (m-CH_Ar), 130.2 (o-CH_Ar), 135.4 (i-CH_Ar), 142.6 (p-C_Ar),

electron density 0.12 (–0.13)eÅ^–3, hydrogen atoms calculated and

158.6 (NCN), 177.6 (CO) ppm. IR (neat): ν = 3055 (vw), 3026 (w), refined as riding atoms.

˜

3003 (w), 2968 (m), 2928 (w), 2862 (w), 1682 (m), 1634 (vs), 1612

4-Methyl-N-(pyrrolidin-1-ylmethylene)benzamide (5g): Obtained

(s), 1510 (w), 1452 (w), 1414 (w), 1379 (m), 1366 (m), 1335 (vs),

1260 (vs), 1215 (w), 1186 (w), 1159 (w), 1128 (m), 1084 (vs), 1022

(w), 959 (m), 949 (w), 920 (w), 880 (w), 860 (w), 831 (s), 775 (s),

760 (m), 615 (s) cm^–1. HRMS (ESI): m/z calcd. for C₁₅H₂₃N₂O⁺

247.1805; found 247.1811. C₁₅H₂₂N₂O (246.35): calcd. C 73.13, H

9.00, N 11.37; found C 73.15, H 8.09, N 11.19.

from pyrrolidine-1-carbonitrile (1a; 0.192 g, 2 mmol) and 4-meth-

ylbenzoyl chloride (0.371 g, 0.24 mmol) according to the general

procedure. Pure product 5g (0.352 g, 1.63 mmol, 81%) was ob-

tained by column chromatography (diethyl ether/n-pentane, 3:1 +

10% triethylamine) and HPLC (ethyl acetate/cyclohexane, 1:1) as

1

a colourless solid (m.p. 110 °C). H NMR (400 MHz, CD₂Cl₂): δ

N-[(Diisopropylamino)methylene]pivalamide (5e): Obtained from

N,N-diisopropylcyanamide (1d; 0.252 g, 2 mmol) and pivaloyl

chloride (0.289 g, 0.24 mmol) according to the general procedure.

Pure product 5e (0.430 g, 1.75 mmol, 87%) was obtained after col-

umn chromatography (diethyl ether/n-pentane, 1:5 + 10% triethyl-

amine) and HPLC (ethyl acetate/cyclohexane, 1:5) as a colourless

solid (m.p. 72 °C). ¹H NMR (300 MHz, CD₂Cl₂): δ = 1.15 [s, 9 H,

= 1.99 (m, 4 H, NCH₂CH₂), 2.39 (s, 3 H, Aryl-CH₃), 3.64 (m, 4

3

H, NCH₂), 7.22 (d, J_H,H= 8.2 Hz, 2 H, m-CH_Ar), 8.13 (d, J_H,H

= 8.2 Hz, 2 H, o-CH_Ar), 8.77 (s, 1 H, NCHN) ppm. ¹³C NMR

(100 MHz, CD₂Cl₂): δ = 21.8 (Aryl-CH₃), 25.5, 24.9 (NCH₂CH₂),

50.3, 46.8 (NCH₂), 129.1 (m-CH_Ar), 130.2 (o-CH_Ar), 135.0 (i-C_Ar),

142.7 (p-C_ArCH ), 157.6 (NCHN), 177.6 (CO) ppm. IR (neat): ν =

˜

3

3075 (vw), 3021 (w), 2970 (m), 2922 (w), 2876 (w), 2361 (vw), 2340

(vw), 1726 (vw), 1636 (s), 1591 (vs), 1562 (vs), 1504 (m), 1472 (m),

1441 (s), 1348 (s), 1333 (s), 1304 (s), 1294 (s), 1252 (s), 1190 (s),

1173 (s), 1161 (s), 1113 (m), 1082 (s), 1040 (s), 1016 (s), 993 (s),

970 (s), 932 (s), 916 (s), 901 (s), 856 (s), 841 (s), 806 (s), 777 (s),

3

C(O)C(CH₃)₃], 1.28 (d, J_H,H= 6.8 Hz, 6 H, CH₃), 1.31 (d, J_H,H

3

=

6.8 Hz, 6 H, CH₃), 3.67 [hept, J_H,H= 6.8 Hz, 1 H,

3

NCH(CH₃)₂], 4.38 [hept, J_H,H= 6.8 Hz, 1 H, NCH(CH₃)₂], 8.46

(s, 1 H, NCHN) ppm. ¹³C NMR (75 MHz, CD₂Cl₂): δ = 23.9, 20.2

[NCH(CH₃)₂], 28.0 [C(O)C(CH₃)₃], 48.3, 49.7, [NCH(CH₃)₂], 157.7 760 (vs), 692 (s), 664 (m), 637 (s), 602 (m), 581 (m), 563 (m), 538

(NCN), 192.3 (CO) ppm. IR (neat): ν = 2994 (m), 2968 (s), 2955 (m), 528 (m), 513 (m), 500 (s), 488 (vs) cm^–1. HRMS (ESI): m/z

˜

(m), 2930 (w), 2901 (w), 2870 (w), 2361 (w), 2344 (w), 1636 (s),

1568 (vs), 1549 (s), 1477 (s), 1450 (m), 1387 (vs), 1371 (vs), 1356 (216.28): calcd. C 72.19, H 7.46, N 12.95; found C 71.68, H 7.40,

calcd. for C₁₃H₁₇N₂O⁺217.1335; found 217.1339. C₁₃H₁₆N₂O

(s), 1331 (m), 1283 (m), 1217 (w), 1207 (m), 1180 (m), 1165 (m),

1125 (s), 1109 (vs), 1030 (m), 1016 (s), 937 (w), 924 (m), 899 (w),

883 (w), 862 (w), 820 (w), 777 (w), 741 (w), 667 (w), 604 (m), 590

(w), 559 (m) cm^–1. HRMS (ESI): m/z calcd. for C₁₂H₂₅N₂O⁺

213.1961; found 213.1960. C₁₂H₂₄N₂O (212.33): calcd. C 67.88, H

11.39, N 13.19; found C 67.65, H 11.07, N 13.16.

N 12.70.

N-(Pyrrolidin-1-ylmethylene)pivalamide (5h): Obtained from pyr-

rolidine-1-carbonitrile (1a; 0.192 g, 2 mmol) and pivaloyl chloride

(0.289 g, 0.24 mmol) according to the general procedure. Pure

product 5h (0.109 g, 0.60 mmol, 30%) was obtained by column

chromatography (diethyl ether/n-pentane, 2:1 + 10% triethylamine)

and HPLC (ethyl acetate/cyclohexane, 8:1) as a colourless solid

(m.p. 61 °C). ¹H NMR (300 MHz, CD₂Cl₂): δ = 0.94–1.11 (m, 4

N-(Pyrrolidin-1-ylmethylene)benzamide (5f): Obtained from pyrrol-

idine-1-carbonitrile (1a; 0.192 g, 2 mmol) and benzoyl chloride

(0.337 g, 0.24 mmol) according to the general procedure. Pure

product 5f (0.241 g, 1.19 mmol, 60%) was obtained by column

chromatography (diethyl ether/n-pentane, 3:1 + 10% triethylamine)

and HPLC (ethyl acetate/cyclohexane, 1:2) as a colourless solid

3

H, NCH₂CH₂), 1.54 [s, 9 H, C(CH₃)₃], 2.49 (t, J_H,H= 6.7 Hz, 2

3

H, NCH₂), 3.08 (t, J_H,H= 9.3 Hz, 2 H, NCH₂), 8.54 (s, 1 H,

NCHN) ppm. ¹³C NMR (75 MHz, CD₂Cl₂): δ = 24.9, 25.5

(NCH₂CH₂), 28.3 [NC(CH₃)₃], 41.2 [NC(CH₃)₃], 45.6, 48.5

1

(m.p. 69–70 °C). H NMR (400 MHz, CD₂Cl₂): δ = 1.95–2.01 (m,

(NCH ), 156.9 (NCHN), 191.3 (CO) ppm. IR (neat): ν = 2972 (m),

˜

2

4 H, NCH₂CH₂), 3.63–3.67 (m, 4 H, NCH₂), 7.38–7.41 (m, 2 H, 2961 (s), 2926 (m), 2864 (m), 2361 (m), 2344 (m), 1643 (vs), 1576

m-CH_Ar), 7.46–7.49 (m, 1 H, p-CH_Ar), 8.15–8.31 (m, 2 H, o-CH_Ar), (vs), 1553 (s), 1477 (s), 1443 (s), 1410 (s), 1385 (m), 1346 (s), 1331

8.78 (s, 1 H, NCHN) ppm. ¹³C NMR (100 MHz, CD₂Cl₂): δ =

(s), 1310 (vs), 1292 (s), 1223 (m), 1177 (s), 1123 (vs), 1111 (vs),

24.9, 25.5 (NCH₂CH₂), 46.9, 50.3 (NCH₂), 128.4 (m-CH_Ar), 130.1 1020 (m), 970 (w), 935 (m), 914 (m), 866 (m), 818 (m), 779 (m),

(o-CH_Ar), 132.1 (p-CH_Ar), 137.7 (i-C_Ar), 157.7 (NCN), 177.5 737 (m), 640 (m), 617 (m), 586 (s), 517 (w), 494 (vs) cm^–1. HRMS

(CO) ppm. IR (neat): ν = 3080 (w), 3055 (w), 2963 (w), 2953 (w),

(ESI): m/z calcd. for C₁₀H₁₉N₂O⁺183.1492; found 183.1503.

˜

2878 (m), 1632 (s), 1580 (s), 1558 (vs), 1487 (m), 1477 (m), 1464

(m), 1450 (s), 1441 (s), 1344 (s), 1327 (s), 1310 (vs), 1290 (m), 1254

(s), 1244 (s), 1229 (s), 1186 (m), 1153 (s), 1117 (m), 1084 (s), 1063

(s), 1034 (s), 1018 (s), 974 (w), 961 (w), 930 (w), 918 (w), 903 (w),

874 (w), 853 (w), 816 (w), 808 (w), 787 (w), 714 (vs), 687 (s), 646

(m), 617 (w), 581 (w), 563 (w), 542 (w), 530 (w), 521 (w), 505 (w),

498 (w), 486 (m), 474 (s), 463 (s), 451 (vs), 424 (vs) cm^–1. HRMS

(ESI): m/z calcd. for C₁₂H₁₅N₂O⁺203.1179; found 203.1173.

C₁₂H₁₄N₂O (202.26): calcd. C 71.26, H 6.98, N 13.85; found C

71.17, H 7.08, N 13.55.

N-(Morpholinomethylene)benzamide (5i): Obtained from pyrrol-

idine-1-carbonitrile (1a; 0.192 g, 2 mmol) and benzoyl chloride

(0.337 g, 0.24 mmol) according to the general procedure. Pure

product 5i (0.311 g, 1.39 mmol, 70%) was obtained by column

chromatography (diethyl ether/n-pentane, 3:1 + 10% triethylamine)

and HPLC (ethyl acetate/cyclohexane, 8:1) as a colourless solid

(m.p. 100–102 °C). ¹H NMR (300 MHz, CD₂Cl₂): δ = 3.54 (t, ³J_H,H

3

= 5 Hz, 2 H, NCH₂), 3.73–3.77 [m, 4 H, O(CH₂)₂], 3.92 (t, J_H,H

= 5 Hz, 2 H, NCH₂), 7.37–7.45 (m, 2 H, m-CH_Ar), 7.47–7.53 (m,

1 H, p-CH_Ar), 8.24 (m, 2 H, o-CH_Ar), 8.66 (s, 1 H, NCHN) ppm.

¹³C NMR (75 MHz, CD₂Cl₂): δ = 44.8, 51.0 (NCH₂), 66.7, 67.6

(OCH₂), 128.5 (m-CH_Ar), 130.2 (o-CH_Ar), 132.4 (p-CH_Ar), 137.4 (i-

X-ray Crystal Structure Analysis of 5f:^[25]C₁₂H₁₄N₂O; M = 202.25;

colourless crystal; 0.40ϫ0.20ϫ0.15 mm; a = 9.6827(4), b =

10.7414(6), c = 11.2930(8) Å, β = 114.543(3)°; V = 1068.42(11) Å³;

ρ_calc= 1.257 gcm^–3; μ = 0.651 mm^–1; empirical absorption correc-

tion (0.780 Յ T Յ 0.908); Z = 4; monoclinic; space group P2₁/n

(No. 14); λ = 1.54178 Å; T = 223(2) K; ω and φ scans, 6233 reflec-

C_Ar), 159.9 (NCHN), 177.9 (CO) ppm. IR (neat): ν = 3082 (vw),

˜

3063 (vw), 2988 (vw), 2968 (m), 2932 (w), 2876 (w), 2361 (w), 2330

(vw), 1632 (m), 1582 (s), 1570 (s), 1555 (vs), 1485 (w), 1464 (m),

1441 (m), 1431 (m), 1339 (vs), 1325 (vs), 1310 (s), 1279 (m), 1269

8

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Synthesis of N-Acyl- and N-Sulfonylformamidines

(s), 1234 (vs), 1219 (m), 1182 (m), 1161 (m), 1123 (s), 1109 (m), H, o-CH_Ar), 8.14 (s, 1 H, NCHS) ppm. ¹³C NMR (75 MHz,

1092 (s), 1067 (s), 1020 (s), 999 (m), 926 (s), 893 (s), 849 (m), 789 CD₂Cl₂):

δ

=

19.8 [NCH(CH₃)₂], 21.1 (Aryl-CH₃), 22.6

(w), 725 (m), 712 (vs), 671 (s), 635 (m), 617 (m), 596 (m) cm^–1.

[NCH(CH₃)₂], 47.6, 49.4 [NCH(CH₃)₂], 126.9 (o-C_Ar), 129.5 (m-

+

HRMS (ESI): m/z calcd. for C₁₂H₁₅N₂O₂219.1128; found

C_Ar), 141.7 (C_q,Ar), 141.9 (C_q,Ar), 156.7 (NCHS) ppm. IR (neat): ν

˜

219.1122. C₁₂H₁₄N₂O₂(218.25): calcd. C 66.04, H 6.47, N 12.84;

found C 65.95, H 6.59, N 12.47.

= 3069 (vw), 3048 (vw), 2986 (w), 2972 (w), 2959 (w), 2930 (w),

2878 (vw), 2359 (vw), 1595 (vs), 1495 (w), 1456 (m), 1387 (w), 1371

(w), 1329 (s), 1304 (s), 1294 (vs), 1283 (vs), 1196 (s), 1148 (vs), 1136

(s), 1086 (vs), 1042 (w), 1032 (w), 1018 (w), 916 (m), 887 (vs), 839

(vs), 818 (vs), 741 (s), 708 (vs), 669 (vs), 592 (vs), 569 (m), 538

(vs) cm^–1. HRMS (ESI): m/z calcd. for C₁₄H₂₃N₂O₂S⁺283.1475;

found 283.1472. C₁₄H₂₂N₂O₂S (282.40): calcd. C 59.54, H 7.85, N

9.92; found C 59.65, H 7.93, N 9.98.

4-Methyl-N-(morpholinomethylene)benzamide (5j): Obtained from

pyrrolidine-1-carbonitrile (1a; 0.192 g, 2 mmol) and 4-methylben-

zoyl chloride (0.371 g, 0.24 mmol) according to the general pro-

cedure. Pure product 5j (0.313 g, 1.35 mmol, 68%) was obtained by

column chromatography (diethyl ether/n-pentane, 2:1 + 10% trieth-

ylamine) and HPLC (ethyl acetate/cyclohexane, 2:1) as a colourless

solid (m.p. 112 °C). ¹H NMR (300 MHz, CD₂Cl₂): δ = 1.27 (d,

³J_H,H= 7.2 Hz, 2 H, NCH₂), 2.40 (s, 3 H, Aryl-CH₃), 3.43 (q, ³J_H,H

X-ray Crystal Structure Analysis of 7b:^[25]C₁₄H₂₂N₂O₂S; M =

282.40; colourless crystal; 0.20ϫ0.10ϫ0.05 mm; a = 8.1168(1), b

= 8.9201(1), c = 10.9206(1) Å, α = 97.435(1), β = 105.273(1), γ =

94.890(1)°; V = 750.43(1) Å³; ρ_calc= 1.250 gcm^–3; μ = 1.918 mm^–1;

empirical absorption correction (0.700 Յ T Յ 0.910); Z = 2; tri-

3

= 7.2 Hz, 2 H, OCH₂), 3.67 (q, J_H,H= 7.2 Hz, 2 H, OCH₂), 7.23

3

(d, J_H,H= 8.5 Hz, 2 H, m-CH_Ar), 8.14 (d, J_H,H= 8.2 Hz, 2 H, o-

CH_Ar), 8.63 (s, 1 H, NCHN) ppm. ¹³C NMR (75 MHz, CD₂Cl₂):

δ = 15.0, 12.7 (NCH₂), 21.8 (Aryl-CH₃), 41.2, 47.5 (OCH₂), 129.1

(m-CH_Ar), 130.2 (o-CH_Ar), 132.4 (p-C_Ar), 142.6 (i-C_Ar), 159.9

¯

clinic; space group P1 (No. 2); λ = 1.54178 Å; T = 223(2) K; ω and

φ scans, 8592 reflections collected (Ϯh, Ϯk, Ϯl), [(sinθ)/λ] =

0.60 Å^–1, 2644 independent (R_int= 0.042) and 2400 observed reflec-

tions [IϾ2σ(I)], 177 refined parameters, R = 0.042, wR²= 0.110,

max. (min.) residual electron density 0.20 (–0.37)eÅ^–3, hydrogen

atoms calculated and refined as riding atoms.

(NCHN), 177.7 (CO) ppm. IR (neat): ν = 3032 (w), 2995 (w), 2957

˜

(w), 2930 (w), 2913 (w), 2870 (w), 2864 (w), 2361 (vw), 2326 (vw),

1630 (vs), 1603 (s), 1578 (vs), 1557 (vs), 1504 (m), 1468 (m), 1441

(s), 1362 (s), 1344 (vs), 1327 (vs), 1300 (s), 1269 (s), 1234 (s), 1219

(m), 1184 (w), 1157 (s), 1111 (vs), 1088 (s), 1070 (s), 1030 (m), 1015

(m), 988 (vs), 930 (s), 891 (m), 851 (m), 839 (m), 804 (w), 760 (vs),

691 (m), 644 (w), 638 (m), 606 (s), 594 (w), 507 (w) cm^–1. HRMS

Synthesis of 9c: N,NЈ-Diphenylcarbodiimide (8c; 0.23 mL, 242 mg,

1.25 mmol) was added at room temperature to a solution of di(tert-

butyl)aluminium hydride (354 mg, 2.49 mmol) in toluene (10 mL).

The mixture was stirred for 14 h then the solvent was removed in

vacuo and the residue was dissolved in n-hexane (8 mL); colourless

crystals were formed at 2 °C. Yield 208 mg (0.44 mmol, 35%); m.p.

169 °C. ¹H NMR (400 MHz, C₆D₆, 300 K): δ = 1.25 (s, 36 H,

CMe₃), 3.32 (br. s, 1 H, AlHAl), 6.92 (m, 6 H, p-CH and o-CH),

7.00 (m, 4 H, m-CH); 7.43 (s, 1 H, NCHN) ppm. ¹³C NMR

(100 MHz, C₆D₆, 300 K): δ = 16.4 (CMe₃), 31.5 (CMe₃), 123.9 (o-

C), 126.5 (p-C), 129.8 (m-C), 145.9 (ipso-C), 168.9 (NCN) ppm. IR

+

(ESI): m/z calcd. for C₁₃H₁₇N₂O₂233.1285; found 233.1278.

C₁₃H₁₆N₂O₂(232.28): calcd. C 67.22, H 6.97, N 12.06; found C

66.78, H 7.10, N 11.71.

N,N-Diisopropyl-NЈ-(phenylsulfonyl)formimidamide (7a): Obtained

from N,N-diisopropylcyanamide (1d; 0.252 g, 2 mmol) and benz-

enesulfonyl chloride (0.424 g, 0.24 mmol) according to the general

procedure. Pure product 7a (0.398 g, 1.48 mmol, 74%) was ob-

tained by column chromatography (diethyl ether/n-pentane, 2:1 +

10% triethylamine) and HPLC (ethyl acetate/cyclohexane, 2:1) as

(paraffin, CsI plates): ν = 1663 [m ν(AlH)], 1591 (vw), 1545 [s

˜

a

colourless solid (m.p. 112 °C; 114.5–115 °C^[27]). ¹H NMR

ν(C=N), phenyl], 1462 (vs), 1377 [vs. (paraffin)], 1306 (w), 1236 [w

δ(CH₃)], 1211 (w), 1155 (w), 1078 (vw), 1001 (w), 972 (w), 918 (w),

810 (m), 772 (m), 758 [m ν(CC), ν(CN)], 723 [s (paraffin)], 571 (m),

527 (w), 432 [vw δ(CC), ν(AlC), ν(AlN)] cm^–1. MS (EI, 20 eV,

3

(300 MHz, CD₂Cl₂):

NCH(CH₃)₂], 1.30 [d, J_H,H= 6.8 Hz, 6 H, NCH(CH₃)₂], 3.71

[hept, J_H,H= 6.8 Hz, 1 H, NCH(CH₃)₂], 4.44 [hept, J_H,H

δ

3

=

1.22 [d, J_H,H

=

6.9 Hz,

6

H,

3

=

80 °C): m/z (%) = 421 (47) [M⁺– CMe₃], 365 (5) [M⁺– CMe₃

–

6.8 Hz, 1 H, NCH(CH₃)₂], 7.44–7.52 (m, 3 H, CH_Ar), 7.80–7.83

(m, 2 H, o-CH_Ar), 8.22 (s, 1 H, NCHS) ppm. ¹³C NMR (75 MHz,

CD₂Cl₂): δ = 19.8, 23.7 [NCH(CH₃)₂], 48.6, 49.7 [NCH(CH₃)₂],

126.6 (o-CH_Ar), 129.2 (m-CH_Ar), 132.0 (p-C_Ar), 143.7 (SC_ipso),

butene], 279 (27) [M⁺– AltBu₂– butane], 196 (84) [M⁺– 2AltBu₂],

93 (100) [PhNH₂]. C₂₉H₄₈Al₂N₂(478.65): calcd. C, 72.77; H, 10.11;

N, 5.85; found C, 72.22, H, 9.95, N, 5.63.

157.2 (NCHS) ppm. IR (neat): ν = 3080 (vw), 2994 (w), 2976 (w),

˜

X-ray Crystal Structure Analysis of 9c:^[20]C₂₉H₄₈Al₂N₂; M =

478.65; colourless crystals; 0.35ϫ0.22ϫ0.09 mm; a = 11.3727(2),

b = 16.6859(4), c = 16.7326(3) Å, α = 78.902(1), β = 73.841(1), γ =

2959 (w), 2878 (w), 1597 (vs), 1452 (s), 1375 (m), 1335 (s), 1319

(m), 1294 (m), 1279 (vs), 1194 (m), 1180 (m), 1138 (vs), 1103 (m),

1084 (s), 1001 (m), 916 (m), 889 (s), 837 (s), 770 (m), 748 (vs), 718

(m), 696 (m), 606 (vs), 586 (vs), 559 (vs), 546 (vs), 525 (vs), 513

(vs) cm^–1. HRMS (ESI): m/z calcd. for C₁₃H₂₀N₂O₂SNa⁺291.1138;

found 291.1128. C₁₃H₂₀N₂O₂S (268.37): calcd. C 58.18, H 7.51, N

10.44; found C 58.40, H 7.73, N 10.41.

89.181(1)°;

V = = μ =

2990.16(10) Å³; ρ_calc1.063 gcm^–3;

0.993 mm^–1; empirical absorption correction (0.772 Յ T Յ 0.915);

¯

Z = 4; triclinic; space group P1 (No. 2); λ = 1.54178 Å; T = 153(2)

K; ω and φ scans, 17105 reflections collected (Ϯh, Ϯk, Ϯl), [(sinθ)/

λ] = 0.60 Å^–1, 9460 independent (R_int= 0.0255), 7810 observed re-

N,N-Diisopropyl-NЈ-tosylformimidamide (7b):^[28]Obtained from

N,N-diisopropylcyanamide (1d; 0.252 g, 2 mmol) and 4-toluene-

sulfonyl chloride (0.458 g, 0.24 mmol) according to the general pro-

cedure. Pure product 7b (0.458 g, 1.62 mmol, 81%) was obtained

by column chromatography (diethyl ether/n-pentane, 1:4 + 10% tri-

ethylamine) and HPLC (ethyl acetate/cyclohexane, 2:1) as a colour-

less solid (m.p. 98–100 °C). ¹H NMR (300 MHz, CD₂Cl₂): δ = 0.63

flections [IϾ2σ(I)], 627 refined parameters, R = 0.0469, wR²

=

0.1345, max. (min.) residual electron density 0.477 (–0.241)eÅ^–3,

hydrogen atoms calculated and refined as riding atoms.

General Procedure for the Preparation of N,NЈ-Disubstituted N-

Acylformamidines 10 and N-Sulfonylformamidines 11: The respec-

tive carbodiimide 8 (1 equiv.) was dissolved in toluene (5 mL

[d, ³J_H,H= 6.8 Hz, 1 H, NCH(CH₃)₂], 0.81 [d, ³J_H,H= 6.9 Hz, 1 H, per mmol) and DIBAL-H (1 m in toluene, 2 equiv.) was slowly

NCH(CH₃)₂], 1.89 (s, 3 H, Aryl-CH₃), 2.83 [hept, ³J_H,H= 6.8 Hz, 1

added. After stirring the reaction mixture for 30 min, the electro-

3

H, NCH(CH₃)₂], 4.03 [hept, J_H,H= 6.8 Hz, 1 H, NCH(CH₃)₂], phile (2.2 equiv.) was added and stirring was continued for at least

3

6.84 (d, J_H,H= 7.9 Hz, 1 H, m-CH_Ar), 8.07 (d, J_H,H= 8.2 Hz, 1 2 h. The solvent was removed under reduced pressure, then the

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E.-U. Würthwein et al.

FULL PAPER

crude product was purified by column chromatography and – if

necessary – by HPLC and/or recrystallisation.

(75 MHz, C₆D₆): δ = 20.2 (CH₃), 24.8, 26.0, 26.1, 26.9, 29.4, 35.5

(CH₂), 55.7, 65.2 [CH(CH₂)₂],129.1, 129.3 (CH_Ar), 134.3 (i-C_Ar),

141.1 (p-C_Ar), 148.6 (NCN), 172.0 (CO) ppm. IR (neat): ν = 3337

˜

N-Isopropyl-NЈ-[(isopropylimino)methyl]benzamide (10a): Obtained

from N,N-diisopropylcarbodiimide (8a; 0.252 g, 2 mmol) and ben-

zoyl chloride (0.618 g, 0.44 mmol) according to the general pro-

cedure. Pure product 10a (0.342 g, 1.50 mmol, 75%) was obtained

by column chromatography (cyclohexane/ethyl acetate, 2:1 + 10%

(w), 3154 (s, CH_Ar), 3059 (w, CH_Ar), 2918 (w, CH_aliph.), 2787 (w),

1665 (s, C=O), 1612 (s, C=N), 1568 (s, C=C), 1520 (m, C=C), 1439

(m, C=C), 1410 (s), 1396 (s), 1304 (w), 1287 (w), 1215 (w), 1188

(m), 1144 (w), 1123 (m), 1113 (w), 1040 (w), 1020 (w), 976 (w), 968

(w), 953 (w), 839 (m), 816 (w), 795 (w), 727 (w), 692 (w), 656 (w),

621 (w). HRMS (ESI): m/z calcd. for C₂₁H₃₁N₂O⁺327.2431; found

327.2439. C₂₁H₃₀N₂O (326.24): calcd. C, 77.26; H, 9.26; N, 8.58;

found C, 77.01; H, 9.20; N, 8.45.

1

triethylamine) as a colourless oil. H NMR (300 MHz, C₆D₆): δ =

3

1.02 [d, J_H,H= 6.3 Hz, 6 H, CH(CH₃)₂], 1.56 [d, J_H,H= 6.9 Hz,

6 H, CH(CH₃)₂], 2.85 [hept, ³J_H,H= 6.2 Hz, 1 H, CH(CH₃)₂], 5.18

3

[hept, J_H,H= 6.9 Hz, 1 H, CH(CH₃)₂], 7.02 (m, 3 H, o- und p-

X-ray Crystal Structure Analysis of 10c:^[25]C₂₁H₃₀N₂O; M =

326.47; colourless crystal; 0.35ϫ0.20ϫ0.20 mm; a = 6.4959(3), b

CH_Ar), 7.36 (m, 2 H, m-CH_Ar), 7.95 (s, 1 H, NCHN) ppm. ¹³C

NMR (75 MHz, C₆D₆):

δ = 19.5 {N[CH(CH₃)₂]₂}, 25.0

= 14.2569(6), c = 20.0837(9) Å; V = 1859.98(14) Å³; ρ_calc

=

{N[CH(CH₃)₂]₂}, 47.3 {N[CH(CH₃)₂]₂}, 57.4 {N[CH(CH₃)₂]₂},

128.6 (m-CH_Ar), 128.7 (o-CH_Ar), 130.7 (p-CH_Ar), 136.9 (i-C_Ar),

1.166 gcm^–3; μ = 0.550 mm^–1; empirical absorption correction

(0.830 Յ T Յ 0.898); Z = 4; orthorhombic; space group P2₁2₁2₁

(No. 19); λ = 1.54178 Å; T = 223(2) K; ω and φ scans, 14210 reflec-

tions collected (Ϯh, Ϯk, Ϯl), [(sinθ)/λ] = 0.60 Å^–1, 3267 indepen-

dent (R_int= 0.045) and 3086 observed reflections [IϾ2σ(I)], 218

refined parameters, R = 0.037, wR²= 0.096, max. (min.) residual

electron density 0.12 (–0.13)eÅ^–3, hydrogen atoms calculated and

refined as riding atoms. Flack parameter was refined to 0.2(4).

147.8 (NCN), 171.6 (CO) ppm. IR (neat): ν = 3305 (vw), 3062 (vw,

˜

CH_Ar), 2967 (m, CH_aliph.), 2934 (w, CH_aliph.), 2870 (w, CH_aliph.),

2608 (vw), 2359 (vw), 1705 (vw), 1602 (w, C=C), 1684 (w, C=C),

1670 (w, C=C), 1634 (vs, C=N), 1603 (w), 1582 (w), 1491 (vw),

1449 (w), 1412 (w), 1381 (mw), 1364 (w), 1327 (s, C-C), 1246 (s, C-

C), 1204 (w), 1184 (w), 1159 (m), 1136 (w), 1088 (m), 1028 (w),

1001 (v), 961 (w), 930 (vw), 883 (w), 831 (vw), 818 (vw), 797 (w),

723 (m), 700 (m), 673 (m), 664 (m), 633 (s). HRMS (ESI): m/z

calcd. for C₁₄H₂₁N₂O⁺233.1648; found 233.1644. C₁₄H₂₀N₂O

(232.32): calcd. C 72.38, H 8.68, N 12.06; found C 72.26, H 8.46,

N 12.05.

N-Phenyl-NЈ-[(phenylimino)methyl]benzamide (10d): Obtained from

N,N-diphenylcarbodiimide (8c; 0.388 g, 2 mmol) and benzoyl

chloride (0.763 g, 4.4 mmol) according to the general procedure.

Pure product 10d (0.185 g, 0.62 mmol, 31%) was obtained by col-

umn chromatography (n-pentane/diethyl ether, 2:1 + 10% triethyl-

amine) and subsequent recrystallisation from the eluent as a

N-Isopropyl-N-[(isopropylimino)methyl]-4-methylbenzamide (10b):

Obtained from N,N-diisopropylcarbodiimide (8a; 0.252 g, 2 mmol)

and 4-methylbenzoyl chloride (0.763 g, 4.4 mmol) according to the

general procedure. Pure product 10b (0.216 g, 0.88 mmol, 44%) was

obtained by column chromatography (n-pentane/diethyl ether, 2:1

+ 10% triethylamine) and subsequent HPLC (cyclohexane/ethyl

acetate, 1:3) as a colourless oil. ¹H NMR (400 MHz, C₆D₆): δ =

1

colourless solid (m.p. 130–132 °C). H NMR (400 MHz, C₆D₆): δ

= 6.75–7.15 (m, 13 H, CH_Ar), 7.35–7.40 (m, 2 H, CH_Ar), 9.25 (m,

1 H, NCH) ppm. ¹³C NMR (100 MHz, C₆D₆): δ = 121.7, 125.3,

129.0, 129.4, 129.5, 129.6, 130.9 (CH_Ar), 137.1, 136.2 (i-C_Ar), 149.4

(NCN), 150.3 (i-C_Ar), 170.6 (CO) ppm. IR (neat): ν = 3064 (m,

˜

CH_Ar), 3055 (m, CH_Ar), 3035 (m, CH_Ar), 2362 (m), 2341 (m), 1656

(s, C=O), 1627 (s, C=N), 1589 (s), 1577 (s), 1487 (s), 1444 (m), 1363

(s), 1315 (m), 1294 (m), 1217 (s), 1097 (m), 1026 (s), 983 (m), 912

(m), 844 (s), 754 (s), 715 (s), 688 (s), 661 (s). 651 (m) cm^–1. HRMS

(ESI): m/z calcd. for C₂₀H₁₇N₂O⁺301.1335; found 301.1334.

C₂₀H₁₆N₂O (300.36): calcd. C 79.98, H 5.37, N 9.33; found C

79.64, H 5.73, N 9.29.

3

1.06 [d, J_H,H= 6.3 Hz, 6 H, CH(CH₃)₂], 1.60 [d, J_H,H= 6.9 Hz,

3

6 H, CH(CH₃)₂], 1.98 (s, 3 H, CH₃), 2.90 [hept, J_H,H= 6.3 Hz, 1

H, CH(CH₃)₂], 5.24 [hept, J_H,H= 6.9 Hz, 1 H, CH(CH₃)₂], 6.83

(d, J_H,H= 7.8 Hz, 2 H, m-CH_Ar), 7.35 (d, J_H,H= 7.8 Hz, 2 H, o-

CH_Ar), 8.02 (s, 1 H, NCH) ppm. ¹³C NMR (100 MHz, C₆D₆): δ =

19.5, 25.0 [CH(CH₃)₂], 21.2 (CH₃), 47.3, 57.4 [CH(CH₃)₂], 128.0 (o-

CH_Ar), 129.3 (m-CH_Ar), 134.1 (i-C_Ar), 141.0 (p-C_Ar), 148.1 (NCN),

3

X-ray Crystal Structure Analysis of 10d:^[25]C₂₀H₁₆N₂O₂; M =

300.35; colourless crystal; 0.40ϫ0.15ϫ0.10 mm; a = 5.7474(1), b

= 10.9703(2), c = 13.2155(3) Å, α = 112.298(1), β = 93.933(1), γ =

100.708(1)°; V = 748.60(3) Å³; ρ_calc= 1.332 gcm^–3; μ = 0.657 mm^–1;

empirical absorption correction (0.779 Յ T Յ 0.937); Z = 2; tri-

164.83 (CO) ppm. IR (neat): ν = 3063 (w, CH_Ar), 3032 (w, CH_Ar),

˜

2967 (w, CH_aliph.), 2934 (w, CH_aliph.), 2870 (w, CH_aliph.), 2361 (vw),

2342 (vw), 1705 (w, C=C), 1684 (w, C=C), 1670 (m, C=N), 1634

(vs, C=O), 1603 (w), 1582 (w), 1491 (vw), 1449 (w), 1412 (w), 1381

(m), 1364 (w), 1327 (s), 1246 (s), 1204 (w), 1184 (w), 1159 (m), 1136

(w), 1088 (m), 1028 (w), 1001 (vw), 961 (w), 930 (vw), 883 (w), 831

(vw), 797 (w), 723 (m), 700 (m), 673 (m), 664 (m), 633 (s). HRMS

(ESI): m/z calcd. for C₁₅H₂₃N₂O⁺247.1805; found 247.1800.

C₁₅H₂₂N₂O (246.17): calcd. C, 73.13; H, 9.00; N, 11.37; found C,

73.25; H, 9.01; N, 11.25.

¯

clinic; space group P1 (No. 2); λ = 1.54178 Å; T = 223(2) K; ω and

φ scans, 7914 reflections collected (Ϯh, Ϯk, Ϯl), [(sinθ)/λ] =

0.60 Å^–1, 2636 independent (R_int= 0.039) and 2434 observed reflec-

tions [IϾ2σ(I)], 209 refined parameters, R = 0.036, wR²= 0.096,

max. (min.) residual electron density 0.17 (–0.19)eÅ^–3, hydrogen

atoms calculated and refined as riding atoms.

N-Cyclohexyl-NЈ-[(cyclohexylimino)methyl]-4-methylbenzamide (10c):

Obtained from N,N-dicyclohexylcarbodiimide (8b; 0.412 g,

2 mmol) and 4-methylbenzoyl chloride (0.680 g, 4.4 mmol) accord-

ing to the general procedure. Crude product 10c (0.641 g,

1.96 mmol, 98%) was purified on two chromatographic columns

(n-pentane/diethyl ether, 2:1 + 10% triethylamine, then cyclohex-

ane/ethyl acetate, 5:1 + 10% triethylamine) and subsequent HPLC

(cyclohexane/ethyl acetate, 5:1) to give a colourless solid (m.p.

106 °C). ¹H NMR (300 MHz, C₆D₆): δ = 0.74–1.88 (m, 20 H,

CH₂), 2.00 (m, 3 H, CH₃), 2.79 [m, 1 H, CH(CH₂)₂], 4.89 [m, 1 H,

General Procedure for the Preparation of Unsymmetrical N,NЈ-Di-

substituted Formamidines from N-tert-Butyl-N-ethylcarbodiimide

(8d): Carbodiimide 8d (1 equiv.) was dissolved in toluene (5 mL

per mmol) and DIBAL-H (1 m in toluene, 1 equiv.) was slowly

added. After stirring the reaction mixture for 30 min, electrophile

(1.1 equiv.) was added and stirring was continued for at least 2 h.

The solvent was removed under reduced pressure, then the crude

product was purified by column chromatography and – if neces-

sary – by HPLC and/or recrystallisation.

3

CH(CH₂)₂], 6.86 (d, J_H,H= 7.9 Hz, 2 H, m-CH_Ar), 7.40 (d, J_H,HN-[(tert-Butylimino)methyl]-NЈ-ethyl-4-methylbenzamide (10e): Ob-

= 7.9 Hz, 2 H, o-CH_Ar), 8.08 (m, 1 H, NCH) ppm. ¹³C NMR

tained from N-(tert-butyl)-NЈ-ethylcarbodiimide (8d; 0.252 g,

10

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Synthesis of N-Acyl- and N-Sulfonylformamidines

2 mmol) and 4-methylbenzoyl chloride (0.340 g, 2.2 mmol) accord-

ing to the general procedure. Pure product 10e (0.246 g, 1.0 mmol,

50%) was obtained by column chromatography (n-pentane/diethyl

ether, 8:1 + 10% triethylamine) and subsequent HPLC (cyclohex-

N,NЈ-Dicyclohexyl-N-tosylformimidamide (11b): Obtained from

N,N-dicyclohexylcarbodiimide (8c; 0.412 g, 2 mmol) and 4-toluene-

sulfonyl chloride (0.763 g, 4.4 mmol) according to the general pro-

cedure. Pure 11b (0.529 g, 1.46 mmol, 73%) was obtained by col-

umn chromatography (n-pentane/diethyl ether, 2:1 + 10% triethyl-

ane/ethyl acetate, 5:1) as a colourless oil. ¹H NMR (300 MHz,

3

C₆D₆): δ = 1.06 [s, 9 H, C(CH₃)₃], 1.28 (t, J_H,H= 7.0 Hz, 2 H, amine), a second column chromatographic purification (cyclohex-

3

NCH₂CH₃), 1.98 (s, 3 H, Aryl-CH₃), 4.15 (q, J_H,H= 6.9 Hz, 1 H,

ane/ethyl acetate, 5:1 + 10% triethylamine) and subsequent HPLC

(cyclohexane/ethyl acetate, 5:1) as a colourless solid (m.p. 81–

83 °C). ¹H NMR (300 MHz, C₆D₆): δ = 0.90–1.78 (m, 20 H, CH₂),

3

NCH₂CH₃), 6.84 (d, J_H,H= 7.9 Hz, 2 H, m-CH_Ar), 7.28 (d, J_H,H

= 8.0 Hz, 1 H, o-CH_Ar), 8.18 (s, 1 H, NCH) ppm. ¹³C NMR

(75 MHz, C₆D₆): δ = 13.3 (NCH₂CH₃), 21.2 (Aryl-CH₃), 30.3 1.86 (s, 3 H, CH₃), 2.90 [m, 1 H, CH(CH₂)₂], 4.22 [m, 1 H,

3

[C(CH₃)₃], 37.6 (NCH₂CH₃), 54.9 [NC(CH₃)₃], 128.7 (i-C_Ar), 129.2 CH(CH₂)₂], 6.76 (d, J_H,H= 8.0 Hz, 2 H, m-CH_Ar), 7.71 (d, J_H,H

(o-CH_Ar), 133.5 (m-CH_Ar), 140.8 (Aryl-CH₃), 145.5 (NCHN), = 8.0 Hz, 2 H, o-CH_Ar), 8.55 (s, 1 H, NCH) ppm. ¹³C NMR

171.3 (NCO) ppm. IR (neat): ν = 2968 (m), 2934 (w), 2874 (vw),

(75 MHz, C₆D₆): δ = 21.2 (CH₃), 24.8, 25.7, 26.2, 26.8, 29.6, 35.2

˜

1668 (w), 1630 (vs), 1612 (s), 1510 (w), 1450 (w), 1433 (w), 1404 (CH₂), 58.7, 65.5, 127.2, 123.0 (CH_Ar), 139.0 (i-C_Ar), 143.6 (p-C_Ar),

(m), 1366 (s), 1333 (s), 1258 (m), 1206 (m), 1177 (w), 1085 (s), 1022 145.3 (NCN) ppm. IR (neat): ν = 2929 (s, CH_aliph.), 2922 (s, CH_al-

˜

(w), 937 (w), 874 (w), 754 (m), 631 (m), 606 (m), 550 (m), 540 (m), _iph.), 2827 (w, CH_aliph.), 2358 (m), 2343 (m), 2331 (m), 1645 (s,

515 (m), 494 (s), 459 (s), 447 (s), 420 (s). HRMS (ESI): m/z calcd.

C=N), 1597 (m), 1494 (m), 1454 (s), 1361 (s), 1332 (s), 1219 (s),

for C₁₅H₂₃N₂O⁺247.1805; found 247.1792. C₁₅H₂₂N₂O (246.17): 1161 (s), 1153 (s), 1161 (s), 1153 (s), 1024 (s), 989 (s), 958 (s), 893

calcd. C, 73.13; H, 9.00; N, 11.37; found C, 72.90; H, 8.84; N,

11.45.

(m), 813 (s), 756 (s), 669 (s), 664 (m), 615 (m). HRMS (ESI): m/z

calcd. for C₂₀H₃₁N₂O₂S⁺363.2101; found 363.2107. C₂₀H₃₀N₂O₂S

(362.53): calcd. C 66.26, H 8.34, N 7.73; found C 65.94, H 8.45, N

7.73.

N-[(tert-Butylimino)methyl]-N-ethylpivalamide (10f): Obtained from

N-(tert-butyl)-NЈ-ethylcarbodiimide (8d; 0.252 g, 2 mmol) and piv-

aloyl chloride (0.265 g, 2.2 mmol) according to the general pro-

cedure. Pure 10f (0.065 g, 0.31 mmol, 15%) was obtained by col-

umn chromatography (n-pentane/diethyl ether, 10:1 + 10% triethyl-

amine) and subsequent HPLC (cyclohexane/ethyl acetate, 5:1) as a

X-ray Crystal Structure Analysis of 11b:^[25]C₂₀H₃₀N₂O₂S; M =

362.52; colourless crystal; 0.50ϫ0.12ϫ0.05 mm; a = 5.6170(1), b

= 19.7269(4), c = 17.5765(4) Å, β = 90.706(1)°; V = 1947.43(7) Å³;

ρ_calc= 1.236 gcm^–3; μ = 0.182 mm^–1; empirical absorption correc-

tion (0.914 Յ T Յ 0.991); Z = 4; monoclinic; space group P2₁/c

(No. 14); λ = 0.71073 Å; T = 223(2) K; ω and φ scans, 14930 reflec-

tions collected (Ϯh, Ϯk, Ϯl), [(sinθ)/λ] = 0.60 Å^–1, 3357 indepen-

dent (R_int= 0.056) and 2901 observed reflections [IϾ2σ(I)], 227

refined parameters, R = 0.048, wR²= 0.128, max. (min.) residual

electron density 0.22 (–0.39)eÅ^–3, hydrogen atoms calculated and

refined as riding atoms.

1

colourless oil. H NMR (300 MHz, C₆D₆): δ = 1.15 [s, 9 H, C(O)-

3

C(CH₃)₃], 1.16 [s, 9 H, NC(CH₃)₃], 1.19 (t, J_H,H= 7.0 Hz, 3 H,

3

NCH₂CH₃), 4.06 (q, J_H,H= 6.9 Hz, 2 H, NCH₂CH₃), 8.45 (s, 1

H, NCH) ppm. ¹³C NMR (75 MHz, C₆D₆): δ = 13.3 (NCH₂CH₃),

28.6 [C(O)C(CH₃)₃], 30.6 {NC(CH₃)₃, 37.7 [NC(CH₃)₃]}, 39.9

(NCH₂CH₃), 55.0 [C(O)C(CH₃)₃], 145.1 (NCHN), 177.0

(NCO) ppm. IR (neat): ν = 2970 (m), 2934 (w), 2911 (vw), 2876

˜

(vw), 2361 (vw), 1670 (m), 1630 (vs), 1508 (vw), 1476 (m), 1433

(vw), 1408 (w), 1362 (m), 1344 (w), 1314 (m), 1261 (m), 1198 (s),

1107 (s), 1026 (vw), 947 (w), 885 (vw), 824 (w), 662 (w), 631 (s),

596 (w), 550 (s), 542 (s), 530 (s), 505 (vs), 491 (vs), 484 (vs), 474

(vs), 463 (vs), 432 (vs), 426 (vs), 417 (vs), 407 (vs). HRMS (ESI):

m/z calcd. for C₁₂H₂₅N₂O⁺213.1961; found 213.1980. C₁₂H₂₄N₂O

(212.19): calcd. C, 67.88; H, 11.39; N, 13.19; found C, 67.51; H,

11.22; N, 13.18.

NЈ-tert-Butyl-N-ethyl-N-tosylformimidamide (11c): Obtained from

N-(tert-butyl)-NЈ-ethylcarbodiimide (8d; 0.252 g, 2 mmol) and 4-

toluenesulfonyl chloride (0.419 g, 2.2 mmol) according to the gene-

ral procedure. Pure 11c (0.065 g, 0.31 mmol, 15%) was obtained by

column chromatography (n-pentane/diethyl ether, 4:1 + 10% trieth-

ylamine) and subsequent HPLC (cyclohexane/ethyl acetate, 5:1) as

a colourless solid (m.p. 82–84 °C). ¹H NMR (300 MHz, C₆D₆): δ

3

= 1.11 [s, 9 H, NC(CH₃)₃], 1.16 (t, J_H,H= 7.0 Hz, 2 H,

N,NЈ-Diisopropyl-N-tosylformimidamide (11a): Obtained from N,N-

diisopropylcarbodiimide (8a; 0.252 g, 2 mmol) and 4-toluenesulf-

onyl chloride (0.835 g, 4.4 mmol) according to the general pro-

cedure. Pure 11a (0.407 g, 1.44 mmol, 72%) was obtained by col-

umn chromatography (n-pentane/diethyl ether, 2:1 + 10% triethyl-

amine) and subsequent HPLC (cyclohexane/ethyl acetate, 2:1) as a

colourless solid (m.p. 61 °C). ¹H NMR (300 MHz, C₆D₆): δ = 1.06

3

NCH₂CH₃), 1.84 (s, 3 H, Aryl-CH₃), 3.64 (q, J_H,H= 7.0 Hz, 1 H,

3

NCH₂CH₃), 6.71 (d, J_H,H= 8.0 Hz, 1 H, m-CH_Ar), 7.62 (d, J_H,H

= 8.3 Hz, 1 H, o-CH_Ar), 8.44 (s, 1 H, NCHN) ppm. ¹³C NMR

(75 MHz, C₆D₆): δ = 21.1 (Aryl-CH₃), 13.2 (NCH₂CH₃), 30.3

[NC(CH₃)₃], 39.2 (NCH₂CH₃), 55.1 [NC(CH₃)₃], 128.6 (o-CH_Ar),

130.0 (m-CH_Ar), 138.6 (i-C_Ar), 142.8 (p-C_Ar), 143.6 (NCHN) ppm.

IR (neat): ν = 3053 (w), 2968 (m), 2934 (w), 2874 (w), 1649 (vs),

˜

3

[d, J_H,H= 6.3 Hz, 6 H, CH(CH₃)₂], 1.33 [d, J_H,H= 6.9 Hz, 6 H,

1599 (w), 1497 (w), 1452 (w), 1379 (w), 1362 (m), 1344 (m), 1331

(m), 1308 (m), 1250 (m), 1204 (m), 1177 (s), 1155 (s), 1123 (w),

1090 (m), 1032 (w), 1020 (m), 1009 (s), 978 (m), 961 (w), 893 (s),

816 (m), 800 (w), 772 (vw), 731 (s), 658 (s), 583 (s), 554 (s), 542 (s),

490 (s). HRMS (ESI): m/z calcd. for C₁₄H₂₂N₂O₂S⁺283.1475;

found 283.1472. C₁₄H₂₁N₂O₂S (281.39): calcd. C 59.54, H 7.85, N

9.92; found C 59.21, H 7.95, N 9.81.

3

CH(CH₃)₂], 1.83 (s, 3 H, CH₃), 3.13 [sept, J_H,H= 6.3 Hz, 1 H,

3

H(CH₃)₂], 4.44 [sept, J_H,H= 6.9 Hz, 1 H, CH(CH₃)₂], 6.70 (d,

³J_H,H= 7.6 Hz, 2 H, m-CH_Ar), 7.64 (d, J_H,H= 7.6 Hz, 2 H, o-

3

CH_Ar), 8.49 (s, 1 H, NCH) ppm. ¹³C NMR (75 MHz, C₆D₆): δ =

19.5, 25.1 [CH(CH₃)₂], 21.1 (CH₃), 50.5, 58.1 [CH(CH₃)₂], 127.3,

129.9 (CH_Ar), 138.5 (i-C_Ar), 143.6 (p-C_Ar), 144.8 (NCN) ppm. IR

(neat): ν = 3001 (w, CH_Ar), 2986 (s, CH_aliph.), 2931 (s, CH_aliph.),

˜

2872 (s, CH_aliph.), 2360 (w), 2341 (w), 1681 (w), 1651 (vs, C=N),

1598 (m), 1465 (m), 1454 (m), 1384 (s, SO2), 1348 (s), 1307 (w),

X-ray Crystal Structure Analysis of 11c:^[25]C₁₄H₂₂N₂O₂S; M =

282.40; colourless crystal; 0.20ϫ0.13ϫ0.02 mm; a = 18.1418(9), b

1236 (m), 1192 (s), 1168 (s), 1151 (m), 1085 (s), 1010 (s), 931 (s), = 7.3029(4), c = 12.9482(7) Å, β = 104.649(2)°; V = 1659.71(15) Å³;

893 (w), 840 (m), 813 (w), 667 (s), 632 (s). HRMS (ESI): m/z calcd. ρ_calc= 1.130 gcm^–3; μ = 1.735 mm^–1; empirical absorption correc-

for C₁₄H₂₃N₂O₂S⁺283.1475; found 283.1468. C₁₄H₂₂N₂O₂S

(282.23): C, 59.54; H, 7.85; N, 9.92; found C, 59.32; H, 7.94; N,

9.69.

tion (0.723 Յ T Յ 0.966); Z = 4; monoclinic; space group P2₁/c

(No. 14); λ = 1.54178 Å; T = 223(2) K; ω and φ scans, 13199 reflec-

tions collected (Ϯh, Ϯk, Ϯl), [(sinθ)/λ] = 0.60 Å^–1, 2762 indepen-

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E.-U. Würthwein et al.

FULL PAPER

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Received: February 7, 2013

Published Online: ᭿

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E.-U. Würthwein et al.

FULL PAPER

Hydroalumination

J. Hellmann, I. Rhotert, H. Westenberg,

R. Fröhlich, B. Wibbeling, W. Uhl,

E.-U. Würthwein* ........................... 1–14

N-Acyl- and N-Sulfonylformamidines from

Cyanamides and Carbodiimides by Hydro-

alumination and Subsequent Treatment

with Electrophiles

Keywords: Acylation / Aluminium / Syn-

thetic methods / Hydrides / Density func-

tional calculations

In a simple one-pot procedure cyanamides

are converted into NЈ,NЈ-disubstituted N-

acyl- or N-sulfonylformamidines by hydro-

alumination and subsequent treatment

with acyl- or sulfonyl chlorides. Carbodi-

imides react similarly, forming N,NЈ-disub-

stituted N-acyl- and N-sulfonylformamid-

ines. The intermediate aluminium com-

pounds and several products were charac-

terised, including by X-ray crystallography.

14

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Article Doi

N-acyl- and N-sulfonylformamidines from cyanamides and carbodiimides by hydroalumination and subsequent treatment with electrophiles

DOI: 10.1002/ejoc.201300208

Source and publish data:

Authors:

Article abstract of DOI:10.1002/ejoc.201300208

Full text of DOI:10.1002/ejoc.201300208

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