Asymmetric synthesis of β-hydroxythioacetamides mediated by enantiomerically pure sulphiny1 derivatives

otMwcno/85

s3.00+.00

Q1985lkgamooRouLtd.

Asymmetric

Synthesis

of fl-Hydroxythioacetamides

by Enantiomerically

Mauro

Cinquini,

Pure

Amedea and

Centro

C.N.R.

and

Manfredi,

Angelo

C. Golgi

Derivatives.

Henriette

Holinari

Restelli

Dipartimento

e Industriale Via

Sulphinyl

Mediated

di Chimica

Organica

dell'Universitl

19,

20133

Milano,

Italy.

(ReceivedinUK 3 June 1985)

Abstract. (1) was type

Enantiomerically prepared

starting

condensation

an entry

The recent the

of

and

have

to chiral In

line

recently

also

with

reported

a

number

by others

related

system,

double

this

11

equivalents.

new

chiral

the

Compound

(11

preparation

is possible,

6 months shown

was

excess for

configuration

at sulphur

As mentioned studied

its

(e.e.l.

analogous

aldol

above,

In

60%

compound

agreement

Andersen-type was

assigned

aid

with

syntheses to

having

a chiral

condensation.

Indeed,

as

that

an

synthesis3

and

pointed

sulphinyl of

pure

tested out

moiety

which

can

reaction

of the

the J-10

chiral

is

,

be

1

a the

acetate of

with

Multigram

yield.

a

plays and

en01 by

in

for

chirality

chiral

3-(heptafluoropropylhydroxymethylene)-d-camphorate C this reaction is stereospecific. and (11 Euihfc13.

enantiomeric

thought

enantiomerically

tris

collected

as well

toluene-e-sulphinate

the

in

aldol-type

prepared

synthesized

in

with

recognized

asymmetric

source

efficient

is a stable

we

already

menthyl

in the dark. 1 H nmr spectroscopy by

e.e.

enolates.

bases,

the

readily

is

i-)-(S)-

(11

As

the

N,N-dimethylthioacetamide

-metallated

(11

synthon

for

fully

open

valuable.

mediated 8-10 group,

own

group

in 40-90X

their

these

been

meantime

required

available

commercially

our

Aldol-

sulphinyl

diastereoselective

thioacetamide 11 reactions.

in

pattern

substitution

As

in

providing

role,

have

sulphoxide and

the

been

of

to

of 4-7

aldol-type 8

generation

would

e-tolylsulphinyl-N,N-dimethyl enantioselective

has

highly 2 On reported.

been

of

thioacetamides

thioamides

alla,

thioacetamides

toluene-e-sulphinate.

removal

phydroxy

synthetic versatility of 1 The stereoselective years.

condensations

least

(-l-(Sl-menthyl

subsequent

active

inter

sulphinyl-N,N-dimethylthioacetamide

e-tolyl

from

(1)

to optically

application,

entry

pure

scale

stored

for

shift

III

in

huge

amount

the

(+1-(R)

at

reagent

Europium

produced

a

3

of

98% data

absolute

(11. thioacetamide enolate 4929

synthon

generation

available,

from

we

(+)-(R)-(l)

hi. CMQW

4930

followed

by

mixtures.

aldehyde

addition

Subsequent

thioacetamides

removal

(71-(101

'H nmr

spectroscopy

Scheme

1.

gave of

in good

in the

et al.

adducts

the

sulphinyl

to excellent

presence

(Z)-(6)

as

group

e.e..

afforded

once

again

(Scheme

of Eu(hfcl3

diastereoisomeric fl-hydroxy

established

by

11.

S 11 LDA Me

* ..,JJS~

21 (-)-(Sl-p-Tol-i-OMenthy

NMe2

l 4

e-To1

b

NMe2

(+I-(Rldll

11 base 2) RCHO V

R

IyMe2 (71-(101

Me O(+lBF 3

4

(21-(61

NaBH4

0

OH

Nt4e2

R (121

R = Me

(21,

(71

(31,

(8)

(41,

(91,

(111

R = Prl

(51,

(101,

(121

R = Bui

R = Bui

R = Ph

(61

It

must

borohydride shown

by

sulphynil As

be

noted

reduction the

alkylation

of

an entry

to the

conversion

thioamide

expected

that allow

on

of

(1)

behaves

the

basis

(91

into

(111

as a chiral of

hydroxy

previous

thioamide

and

synthesis

ofyamino

(see

experimental).

synthon of a Famine 4-10 on related

work

subsequent alcohols, Thus

as the

carbanion. systems

the

4931

Asymmctricsyntbcsisof/Mlydroxytbioacetam&a

nature

of the

The

be crucial. as

base

Bu&gBr

was

comparable above

reductive

removal with

The

enantiomeric

the

quite

excess,

A

more

showed

condensation

of

discrimination

the

to

and

low

(Na/Hg.

on

the

account

in

of

base

-90°C

(9)

were

chemical

to

such

in

the

ratios

obtained

yields.

(1)

Na2HP04)

extent

for.

was

gave, the

As

after

products

previously'

and

the

result

more

bulky

55%).

gave (8)

as

a had

On

the

moderate opposite

indicated

observed

steric

best

by

C.O.

experimental).

amides,

decreasing

only

(10). (see

enantiomeric

the

(e.e.

not (7)

and

effects

the

90%).

stereoselection

sulphinyl

with

of

Indeed

(e.e.

aldehyde

(9)

Cotton

N.N-dimethyl

increasing

very

hydroxythioamides

those

trend

(7)

isobutyraldehyde

opposite

regular

out

molar

sulphinyl-thioamide

isovaleric

to

at

substrate-base

in

groups

a decrease

respect

which

but

R residue

with

but

magnesium

by working

and

of

difficult

and

a bulky

and

turned

stereoselection.

aldehyde

to

with

(+)-(R)-(l)

hydroxythioamides

sulphinyl

obtained

of

discrimination.

to high

is

with

spectra,

the

of

enolate

temperatures

purities,

acetaldehyde

chirality

substrate)

condensation"

leading

hand

obtained

of

as base,

of

1) was

pivalaldehyde other

were

mol

of chiral

used

moderate

effect

Table

the

higher

aldol

discrimination (see

generate

enantiomeric

mentioned

(7)-(10)

per

a decrease

BuLi

to

results

mol

step,

to

When in

best

(0.75

condensation leading

used

in

the

aldol-type

the

chiral

of

extent

hindrance

of the

aldehyde

R

residue. The and

absolute

hence

in

hydroxyamide

treatment

experimental) the

case

of

was

with

afforded

(S)

absolute

established

compounds

(-l-(5)-(12).

subsequent

have

configuration

the

Alkylation sodium

of

hydroxide

(-j-(12).

Thus

(-l-(10)

I-)-(10).

R

NMe2

R = He

(S)-(

(S)-(B)

R = Bui

(SI-(10)

(31,

(41,

products

with

and

Reaction

l

a further

with

(-j-(9),

Me30+BF4

and

conditions

(see

(+I-(7)

and

(+1-(B)

insight

('1) we

in the

attempted

9)

R = But

stereochemical

the

NMe2

R = Prl

isolation

path of the

of the

condensation

sulphinyl

adducts

(6).+ of

(+)-(R)-(l)

(4a),

Unfortunately

acetophenone

(10).

correlation

with

/u

(S)-(7)

To gain

of compound

S

?JL

aldehydes

case

chemical

configuration.

_

of

by

in phase-transfer

S

R

in the

(7)-(91,

being

(4b)*

the

with

in 95:5

reaction

Pr'CHO ratio,

is

afforded which

limited

to

only

could

two

be

aldehydes,

diastereoisomeric

separated

ketones

unreactive.

+ Compound (2) is unstable and must be directly desulphurized. 5 With a.b we indicate diastereoisomeric products.

by flash

such

as

M. CINQUINI et al.

4932

chromatography.

This

stereoselection

is

behaviour

not

of

formation

however minor

of

flash

ButCHO two

reaction

(3bI

A tentative

with

which

lead

was

assignment

isolated of

anti

C rests on the values of the B anti isomers (4a) and (3b) J = 7.15 isomers

(4b)

namely

values, sulphinyl

and

amide

with

major

diastereoisomer

= 8.5

Hz.

in both (6)

Thus

Table

Hz

behaves

in extensive

1. Enantioselective

R

of

=

was

all retro

in

66:33

Hz

and

4.1

Hz were

group,

a

(1)

resulted in 1 H nmr); (by

ratio

decomposition

PhCHO

was

respectively. for

condensed 9:1

in the

attempts

Hz,

observed'

anti

of

the

at

C,

for

the

for

the

(Similar adduct

of

a

a 3JH-Ca-C

-H

being

B predominant

desulphurization

of

aldol-reaction.

(+)-(R)-(l)

of p-hydroxythioacetamides

and

(7)-(10)

from

RCHO. 25 b

Yielda

D

e.e.

20

C

"D

(%I

d,e

75

+ 87.5

64

1.547

Me

8uLifse

15

+ 80

59

1.547

Bui

ButMgBr d,e

52

+ 41.5

40

PrL

BuhgBr

75

-105.0

90

1.520

Pri

BuiMgBrg

67

-100.0

81

1.520

Prl

BuLifge

15

-103.0

88

1.520

But

BuhgBr

40

- 63.0

55

1.528

Me

d,e

d,e

a Overall yields of (7)-(10) from (+)-(R)-(l). b c 1, CHCl 3' with the ' As determined by 'H NHR spectroscopy d 0.75

Mol.

equiv.

of

g 0.5

Mol.

temperature

equiv.

of

-78°C.

aid

of Eu(hfc13.

base.

e Condensation time 60 min. f 1.1 Mol. equiv. of base. base;

a

(+)-(R)-(l)

with

adduct

of reductive

the

with

ratio,

(%I

Bu&gBr

complete

case,

sulphinyl

in trace amounts. 11 relative stereochemistry or syn 35 H-Ca-C -H; coupling constants B Hz and J = 6.7 Hz, respectively,

Pr'CHO,

synthesis

Base

this

the

preferential

obtained

like

in

to

only

4.0

Uhen

a

sulphinylthioamide

the

J = 3.7

PriCHO).

Unfortunately

enolates

J

and

(anti)

PhCHO

cases.

resulted

(3a1,

J = 7.6

least

(3a,b)

to

and

syn

at

carbon

diastereoisomers

chromatography

product

that,

at the 7,8,10

unprecedented.

In the case the

indicates achieved

condensation

condensation

temperature

time

60 min.

-90°C.

condensation

4933

Asymmetricsyntbosisof/?-hydfoxytbioaatamides

Table

2. Diastereoselective magnesium

R

enolate

Yield

synthesis of

of

(+)-(R)-(l)

adducts and

(41

and

(61

[I

25c,d

m.p.

aD

BUL

85

66:33e

-94.5

130-132

Prl

77

95:5

-97.1

Ph

55

9O:lO

-71.5

138-140 f

a 0.75

Mol.

equiv.

time 60 min. b . Diastereoisomeric

of

Bu&gBr;

ratio

(d.r.1

condensation

was

from

RCHO.a

d.r.b

(961

(31,

temperature

established

by

-90°C;

'H NMR

C

condensation

spectroscopy.

' Of the major diastereoisomer. d c 1 in CHC13. e By 'H NMR. f Waxy solid

nD 25 1.595.

EXPERIMENTAL.

1 WP-80 and on a Varian H and l3 C NHR spectra were recorded on a Bruker XL-200 instruments, using tetramethylsilane as internal standard and CDCl measured on a Perkin Elmer 247 as solvent. Optical rotations were Elemental analyses were performed with a Perkin Elmer 240 spectrometer. Circular dichroism spectra were obtained with a Jobin-Yvonne instrument. Mark III dichrograph. Silica gel was used for analytical and column chromatography. Organic extracts were dried over sodium sulphate and filtered before removal of the solvent under reduced pressure. Anhydrous solvents were distjlled under nitrogen atmosphere before use, THF and diethylether from lithium alluminium hydride, methanol from magnesium turnings. All reactlons employing anhydrous solvents were run under argon. Aldehydes were commercial products and were distllled before use; (-l-($4 menthyl-e-toluene sulphingte. commercially available from Fluka. had U = -202.5 (c = 1, aceiqne) . N,N-dimethylthioacetamlde was prepared fol FowI! ng a reported procedure and cryfj allized from ethyl acetate: petroleum ether 2:l. It had m.p. 73-74°C (lit. m.p. 74OC). Synthesis of (+I-(RI sulphlnylthioacetamlde (1). To a strrred solution of dlisopropylamine (2.9 ml, 20 mmol) in THF (50 ml) at 0°C. a 1.35 N solution of n-BuLl in hexane (15 ml1 was added. The mixture stirred at 0°C for 15 was min. then -78°C and cooled at N.N-dimethylthioacetamide (20 mmoll In THF (20 al) was added dropwise. The reaction was warmed up at -4OOC. cooled again at -78°C and a solutlon of

4934

M. ClNQUINl rfa/.

(-I-(S)-menthyl toluene-p-sulphinate (2.94 g, 10 mmol) in THF (20 ml) was added and stirring was continued at -78'C for 15 min. The reaction was quenched with saturated ammonium chloride solution (30 ml) and the organic phase separated. The aqueous phase was extracted twice with dichloromethane (100 ml), and the combined organic phases dried and evaporated in vacua. The resulting oil was washed with pentane and then with diisopropylether to make it solid. It was crystallized from a2vixture ethyl acetate: petroleum ether 2:1, m.p. 96-98°C; yield 60%. = +176.1 (c = 1. CHCl 1. Found: F% 54.72; H% 6.28; NX 5.76. CllH15N0 requires: CX 54.74; H% 6.2%; NX 5.80. H NMR: 7.64-7.33 (AA'88' system, 4H'aromatic protons); 4.60-4.06 (A8 system, 2H. CH2-SO); 3.46-3.25 (2s, 6H, N(CH312); 2.43 (s, 3H, CH3-Ar). Synthesis of (7)-(10). The procedure for (-l-(9) is typical: to a stirred solution of (+I-(R$-(1) (242 mg, 1 mmol) in THF (50 ml) kept at -90°C. a 0.51 N solution of Bu-MgBr in diethylether (or 1.35 N solution of n-8uLi in hexane) was added (see Table 1 for base:substrate molar ratios). The enolate precipitated and gave a white suspension. After 30 min stirring at -90°C isobutyraldehyde (0.28 was added at once. After 2h condensation time the reaction was ml, 3 mmol) quenched by addition of saturated ammonium chloride solution (5 ml) and the organic phase separated. The aqueous layer was extracted twice with dichloromethane (2x5 ml), the combined organic phase dried and evaporated in vacua. The crude residue was taken into dry methanol (15 ml) and anhydrous sodium dihydrogen phosphate (1.2 g) was added. To the resulting slurry, cooled at -2O"C, 10% sodium amalgam (1.7 g) was added in one portion. The mixture was stirred at -20°C for 2 h. then filtered and added of saturated ammonium chloride solution (5 ml). The organic solvent was evaporated in vacua and the resulting aqueous phase extracted twice with dichloromethane (20 ml). The organic phase was dried and concentrated to give a crude oil purified by which was flash-chromatography (diethylether or diethylether/hexane as eluant) to give (-)-(9). Compounds (7)-(10) are thick oils. Compound (7): Cf 48.92; H% 8.90; NX 9.49. C H NOS requires: C% 48.94; HX 8.90; NX 9.51. H NMR 4.42 (bs, lH, OH); 4.146(!? part of an A8X system, lH, CH-0); 3.52-3.32 (2s. 6H. N(CH 1 1; 2.8-2.5 (A8 part of an A8X system, 2H. CH -CH); 1.29-1.28 (d, 3H. CH -iH?. HXT6.10; N% 7.43. C H NOS requires: c£ (8): CX, 57.07; C% 57.09; H% 10.12; N% 7.39. H NNR: 4.3-4.2 (X part of an gA EP system, 1H. CH-0); 3.5-3.3 (2s, 6H, N(CH 1 1; 2.7-2.5 (A8 part of an A8X system, 2H. CH -C=S); 1.95-1.8 (M part of an3AiHX system, lH, CH(CH I I; 1.6, 1.5-1.25, l.lg (A8 part of an ABMX system, 2H, Cti2-CH-(CH 1 ;?.9?,20.96-0.94, 0.93 (dd. 6H, HX !I.sl; N% 7.95. C H NOS requires: Compound (9): C4 54.83; 9.78; N% 7.99. H NMR: 4.16 (bs, 1H. OH); 483!6 (X part of an A8X system, lH, CH-0); 3.51-3.33 (2s. 6H. N(CH 1 1; 2.75-2.64 (A8 part of an A8X system, 1.83-1.67 (m, lH, C&!H3)2); 0.97, 0.96-0.94, 0.93 (dd. 6H, 2H.

(“,,

)CH$;(

’

NOS requires: C% 57.09; H% Com$oind (10): CX 157.06; HX 10.15; NX 7.39. C H N% 7.39. H NMR 3.83-3.75 (X part system, lH, CH-0); 10.12; 8f'% n A8X 3.51-3.33 (2s, 6H, N(CH 1 1; 2.91-2.56 (A8 part of an A8X system, 2H, Cli2-CHI; 2.82-2.80 (d, 13, ?TH); 1.0 (s, 9H, (CH313C). Synthesis of intermediates (31, (4) and (6) via magnesium enolates. The products of condensation between the sulphoxide (+)-(R)-(l) and the aldehydes were obtained as described above. The crude oil was then purified by flash-chromatography (diethyl ether or diethylether/hexane as eluant). The major isomer was obtained pure in each case; physical properties are reported in Table 2. Compounds (31, (4) and (6) are thick oils that become solids when stored in the refrigerator at -2OOC. H NO S requires: C% 58.68; HX Compound (3): Cl 58.70; HX 7.70; NX 4.25. C H: NMR (for the major produEP12?3a? 5.3 (AA'BB' system, 4H. 7.69; NX 4.28. aromatic protons); 4.61-4.44 (m, lH, CH-0); 4.11. 4.06 (d. 1H. CH-SO); (CH 1 N); 2.41 (s, 3H, CH -Arl; 1.6-1.5 (m, lH, 3.18-2.63 (2s. 6H, CH(CH ) 1; 1.27-1.24 (m, ??I?, CH -CH(CH 1 1; 0.96Fa.95-0.92. 0.91 (2d, 6H, = 4.0 Hz. d (for $h2e minor product) (4b): 7.3 (AA'88' (CH 13Cfi); J 4.97-4.72 (m, 1H. CH-0); 4.07. 3.97 (d. 1H. syT$eP, 4H. C#&>f#z protons); CH-SO); 3.13-2.62 (s. 3H, CH -Ar); 1.9 (m, lH, (2s. 6H, (CH3) N); 2.35 1.27-1.24 (m, 2H. CH2-C?i(CH312); 0.92, 0.88383. 0.79 (2d. 6H, -CH-(CH3121;

Asymmetricsyntbcdisof~llydroxytilionc&amide3

Attempts to separate the diastereoisomers by hy lead to extensive decomposition of (3b). : Ci 57.45; HX 7.42; NX 4.47. C H N02S requires: CX 57.47; HX H NHR (for the major produc 15 ?$a): 5.3 (AA'88' system, 4H, 7.40; N% 4.47. 4.67, 4.63-4.59. 4.55 (dd, 1". CH-0); 4.22-4.13 (d, 1". aromatic protons); 2.18-2.14 (111, lH,

lH, CH-0); 3.18-2.25 (2s. 6H. (CH ) N); 2.42 (s, 3H, CH -Ar); 1.6-1.5 (n, 1". CH(CH ) 1; 1.19, 1.02-0.91. 0.d32(2d, 6H, (CH ) CH), 3 963: C%,62.20; HX 6.08; NX 4.06. C H Na 5 requF8$!rC!i ;242:;";% Compound H NMF (for the major proi8c?!: 5.5-7.2 (m, 9H, aromatic 6.09; NX 4.03. 6.00, 5.89 (d, l", CH-0); 4.4 (bs, 1". OH); 4.3, 4.2 (d, l", protons); CH-SO); 2.9-2.4 (2s. 6H, (CH3)2N); 2.24 (5, 3H, CH3-Ar); Jc OH_CH2 = 8.15 case only the major diastereoisomer was obtained to HZ. In this \ ure enough allow the assignement for all the resonances. Synthesis of y-amino-alcohol (11). To a stirred suspension of He O'EF _ (3.70 mmol. 1.2 equiv.) in methylene chloride (3.7 ml) cooled at 0 3 C un d er argon, a solution of (-)-(9) (537.25 mg 3.07 mmol) in methylene chloride (3 ml) was added. The reaction mixture was stirred at 0°C for 5 min, the cooling bath was removed, and stirring was continued for 3 hours. The methylene chloride was removed in vacua, the residue was dissolved in anhydrous metvgnol (5 ml) and the resulting solution was cooled at 0°C. Excess Na8H was added in (300 mg. 8 mmol) portions over 5 minutes. The reaction m1 xture was stirred at 0°C for an additional 5 min. the cooling bath was removed and stirring was continued overnight. The organic solvent was then evaporated in vacua, the residue dissolved in methylene chloride and then filtered to remove the inorganic salts. The solution was treated with 10% aqueous HCl (5 ml), the aqueous layer separated, basified with 10% aqueous NaOH to pH = 10, and extracted with diethylether. The organic solvent was removed under reduced pressure to give compey nd (11) (65% y,&ld) as a thick oil. It had n = 1.542O,[U], = +11.77 (c = 0.6 in CHCl ). Found: CX 66Tl2; HX 13.21; & 9.65. C8HlgN0 requires: C% 66.15; HX 13l.19; HX 9.64. H NMR: 3.6-3.4 (X part of an AEMX system, lH, CH-0); 2.7-2.55 (A8 part of an AECIX system, 2H. E2-CHOH); 2.45-2.3 (CO part of an ABC0 system, 2H, CH -N); 2.24 (M part of an AEHX system, (s, 6". (CH ) -N); 1.6-1.3 1". -CH(CH;?2); 0.97, 0.96-0.94. d.&l (dd, 6H, (CH3)2CH). Conversion of hydroxythioacetamide (10) into hydroxyacetamide (12).15 To a stirred solution of hydroxythioacetamide (10) (0.61 g. 0.323 mmol) in methylene chloride (5 ml), trimethyloxonium fluoroborate (0.57 g. 0.388 mmol) was added. The solution was allowed to stand at r.t. overnight, then treated with an excess at 50% aqueous NaOH and the stirring was continued for 5 days. The organic layer was separated, washed with water (IxlOml), dried and the solvent evaporated under vacuum. The crude oil was purified by flash-chromatoe5aphy (diethylether:meth8nol $5.-5 as eluant) to give (12) in (c 1, CHC13). lit. [U]9 =-70.9 (c 1, CHCl3) for a 90% 20% yield.[a] p =-42 enantiomerica ly enriched compound. The product had8physical and spectral data in agreement with those reported in literature. Enantiomeric excess.determination. The enantiomeric purities of compounds (1) and (7)-(10) were checked by 'H NMR spectroscopy with the aid of the chiral shift reagent Eu(hfc)3 in conditions pre-established with their racemic counterparts, which were prepared by condensation of the lithium enolate of N.N-dimethylthioacetamide with the appropriate aldehyde at -4O'C. A 5:1 substrate: shift reagent molar ratio generally gave satisfactory peak-separation. A goqd agreement between the optical rotation values and the e.e. evaluated by H NMR was observed for (7)-(10). Circular Circular Compound 340 4 ax

dichroism measurements. dichroism measurements were carried on in CHCl c=10s3 mol/l (+)(7) and (+)(8) had two positive Cotton effect (Cl.',.) centered at nm and 4ax 270 nm..

4935

M. CINQvrm lf ul.

4936

Compound negative Compound negative

(-1 C.e. (-1 C.e.

(9) had centered (10) had centered

a positive at 335 ik a pos%ive at ax 330 !%

365

C.e. centered at 4 Ix nm and 270 nm. ;cnax C.e. ten2 %ed at nm and aa, 270 nm.

nm.

and

two

360

nm,

and

two

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