GB1582240A - Process for preparing 2-halo-(benzodioxan-2-yl) ethanol derivatives - Google Patents

Description

(54) PROCESS FOR PREPARING 2-HALO-[BENZODIOXAN-2-YL]ETHANOL DERIVATIVES (71) We, JOHN WYETH & BROTHER LIMITED a British Company of Huntercombe Lane South, Taplow, Maidenhead, Berkshire, SL6 OPH, do hereby declare the invention for which we pray that a patent may be granted to us and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to a process for preparing ethanol derivatives useful as chemical intermediates.

In our copending cognate UK Patent Applications Nos. 51781/76 and 45142/77 (Serial No. 1582239) there are described and claimed compounds of formula

wherein X represents oxygen or sulphur; Y represents -CHOH- or

Z represents

or a direct bond; R represents cycloalkyl having 5 to 7 ring carbon atoms or an optionally substituted aryl, or heteroaryl radical, or when Z is a direct bond R can also represent hydrogen; R1 represents hydrogen or lower alkyl; R2 represents hydrogen, halogen, lower alkyl or lower alkoxy, R3 represents lower alkyl or hydrogen; and and ss each represent hydrogen or together represent a direct bond between the carbon atoms to which they are attached and acid addition and quaternary ammonium salts thereof.

The term "lower" as used herein in connection with a group or molecule means the group or molecule contains 1 to 6 carbon atoms.

Compounds of formula I, wherein Y is CHOH and cc and (3are a direct bond, having the erythro configuration of asymmetric centres are particularly preferred, being active in reducing heart rate. Such erythro compounds of formula I may be prepared by reacting compounds of formula

having the erythro configuration, where R' and R2 are as hereinbefore defined with compounds of formula R-Z-N=C=X (Ill) wherein X, R and Z are as defined in connection with formula I, R being other than hydrogen. Usually the reaction to form the compound of formula I takes place at room temperature.

Erythro compounds of formula II may themselves be prepared by reacting an appropriate erythro 2-halo-1-[1,4-benzo-dioxan-2-yl]ethanol with 4-benzamidopiperidine, hydrolysing the product to remove the benzoyl group to give erythro 4-aminopiperidine derivatives of formula II: which compounds may be alkylated to give 4-loweralkylamino derivatives.

We have now surprisingly found a route for the preparation of the 2-halo-1-[1,4benzodioxan-2-yl-]ethanol derivatives which provides the erythro form in excess of the threo form.

Accordingly, this invention provides a method for preparing an erythro-2-halo-1-[1,4 benzodioxan-2-yl]ethanol having the formula

OH R2- f CH-CH2ho109en (i\) in excess of the threo form, which comprises reducing a ketone of formula

C.

2 f C-CH2 hologen O (V) in which formulae R2 is as hereinbefore defined, with an alkali metal borohydride at a temperature at or below -20 C, e.g. from -20 to -100 , preferably from -50" to -90 , most preferably about -70 C.

This reaction may be carried out in the presence of an alkanol having 1 to 3 carbon atoms, e.g. methanol. When reduction is carried out at about -70 C the erythro isomer can be produced substantially in excess of the threo isomer. For example reduction at -700C in methanol gave a 7:3 ratio of erythro to threo isomer.

The erythro compounds of formula IV may also be used directly in a process for preparing erythro compounds of formula I wherein X represents oxygen, and R is other than hydrogen. Such a process comprises reacting an erythro compound of formula IV with a compound of formula

wherein X, Z, R and Rl are as defined above in connection with formula I; being other than hydrogen. Such a reaction is conveniently carried out.in the presence of base, e.g. an alkali metal carbonate such as potassium carbonate or a lower alkyl amine, e.g. triethylamine, in a suitable inert solvent, e.g. dimethylformamide, dichloromethane, isopropanol.

The following Example 1 illustrates the invention; Example 2 illustrates the use of the intermediate.

EXAMPLE 1 Erythro-1 - (1, 4-Benzod ioxan-2-yl-) -2-bromoethanol 2-Bromoacetyl-1,4-benzodioxan(53.8g) in methanol (500 ml) was cooled to -70 C.

Sodium borohydride (10.3g) was added and the solution stirred at -700C for 12 hours. The solution was treated with hydrobromic acid until acidic and the solvent evaporated. The residue was dissolved in ether and the ether extracts were washed with sodium bicarbonate solution; then water and dried (MgSO4) and evaporated to give a white solid. This was recrystallised eight times from petroleum spirit 60-80 to give 14 grams of the title compound.

EXAMPLE 2 Erythm-4-benzarnido-1 (1, 4-benzodioxan ioxan-2-yl-) -2-hydrnxyethyI}pipeiidine (a) Erythro l-(1,4-benzodioxan-2-yl-)-2-bromoethanol (7.()3g 0.031 m),4benzamidopiperidine (5.59g 0.027m) and triethylamine (4g 0.04m) were refluxed in ethanol (250mls) for 24 hours. The solvent was evaporated and the residue dissolved in chloroform and the chloroform extract washed with water, dried (MgSO4) and evaporated to give a white solid (7.95g 65%). This solid (1.5g) was dissolved in the least amount of methanol and acidified with ethanolic HC1. The title compound crystallised, was filtered off and dried (1.04g) Melting Pt. 246-249"C Microanalysis: C22H"N204.HCl requires C, 63.08%; H, 6.50%; N, 6.69%; Found: C, 62.99%; H, 6.55%; N, 6.39% (b) Erythro 4-amino-1-[2- (1, 4-óenzod ioxan-2-yl-)-2-hyd roxyethyll iperid ine Erythro-4-benzamido l -[2-( l,4-benzodioxan-2-yl-)-2-hydroxyethyl fpiperidine (t4 .23g) prepared according to Example 3(b) was suspended in 6 N hydrochloric acid (250 mls) and boiled under reflux for 8 hours. The solid was filtered off and washed with water. The aqueous filtrate and washings were treated wtih anhydrous potassium carbonate powder until basic and these extracted with chloroform. The combined chloroform extracts were washed with water, dried (MgSO4), and evaporated to give title compound (10.4 g 1(10%).

WHAT WE CLAIM IS: 1. A process for preparing an erythro 2-halo-1-[1,4-benzodioxan-2-yl-]ethanol having the formula

OH 2 CH-CH2hologen O (1V) in excess of the threo isomer, wherein R2 is hydrogen, halogen, lower alkyl or lower alkoxy which comprises reducing at a temperature at or below -20"C, a corresponding compound of formula

0 R24 f C-CHi holc9en with an alkali metal borohydride, in an alkanol solvent having 1 to 3 carbon atoms.

2. A process as claimed in Claim l where halogen is bromine.

3. A process as claimed in Claim 1 or Claim 2 in which solvent is methanol.

4. A process as claimed in any one of Claims l to 3 which is effected at a temperature from -20 C to -100"C.

5. A process as claimed in any one of Claims 1 to 3 which is effected at a temperature about -70";.

6. A process as claimed in Claim I substantially as hereinbefore described with reference to Example l.

7. A compound of formula IV as defined in Claim l whenever prepared by a process as claimed in Claims l to 6.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (7)

**WARNING** start of CLMS field may overlap end of DESC **. and the chloroform extract washed with water, dried (MgSO4) and evaporated to give a white solid (7.95g 65%). This solid (1.5g) was dissolved in the least amount of methanol and acidified with ethanolic HC1. The title compound crystallised, was filtered off and dried (1.04g) Melting Pt. 246-249"C Microanalysis: C22H"N204.HCl requires C, 63.08%; H, 6.50%; N, 6.69%; Found: C, 62.99%; H, 6.55%; N, 6.39% (b) Erythro 4-amino-1-[2- (1, 4-óenzod ioxan-2-yl-)-2-hyd roxyethyll iperid ine Erythro-4-benzamido l -[2-( l,4-benzodioxan-2-yl-)-2-hydroxyethyl fpiperidine (t4 .23g) prepared according to Example 3(b) was suspended in 6 N hydrochloric acid (250 mls) and boiled under reflux for 8 hours. The solid was filtered off and washed with water. The aqueous filtrate and washings were treated wtih anhydrous potassium carbonate powder until basic and these extracted with chloroform. The combined chloroform extracts were washed with water, dried (MgSO4), and evaporated to give title compound (10.4 g 1(10%). WHAT WE CLAIM IS:

1. A process for preparing an erythro 2-halo-1-[1,4-benzodioxan-2-yl-]ethanol having the formula

OH 2 CH-CH2hologen O (1V) in excess of the threo isomer, wherein R2 is hydrogen, halogen, lower alkyl or lower alkoxy which comprises reducing at a temperature at or below -20"C, a corresponding compound of formula

0 R24 f C-CHi holc9en with an alkali metal borohydride, in an alkanol solvent having 1 to 3 carbon atoms.

2. A process as claimed in Claim l where halogen is bromine.

3. A process as claimed in Claim 1 or Claim 2 in which solvent is methanol.

4. A process as claimed in any one of Claims l to 3 which is effected at a temperature from -20 C to -100"C.

5. A process as claimed in any one of Claims 1 to 3 which is effected at a temperature about -70";.

6. A process as claimed in Claim I substantially as hereinbefore described with reference to Example l.

7. A compound of formula IV as defined in Claim l whenever prepared by a process as claimed in Claims l to 6.