Phenylboronic acid compounds and intermediates and processes for the preparation thereof
View Patent ↗Vitamin D derivatives, notably non-steroidal vitamin D derivatives, are prepared from novel disubstituted phenylboronic acid compounds having the formula (I): and also from the novel intermediates having the formulae (1), (2), (3) and (10):
1. A disubstituted phenylboronic acid compound of the following structural formula (I):
in which:
R1 is a hydrogen atom or an alkyl radical having from 1 to 4 carbon atoms,
R2 and R3, which may be identical or different, are each an alkyl radical having from 1 to 4 carbon atoms, and
R4 is the —B(OH) 2 radical or the radical of formula:
2. The disubstituted phenylboronic acid compound as defined by claim 1 , wherein formula (I), each alkyl radical having from 1 to 4 carbon atoms is a saturated or unsaturated, linear or cyclic, optionally branched such radical and can be interrupted by a heteroatom.
3. The disubstituted phenylboronic acid compound as defined by claim 2 , wherein formula (I), each alkyl radical is selected from the group consisting of methyl, ethyl, propyl, isopropyl, cyclopropyl, butyl, isobutyl and tert-butyl radicals.
4. A process for the preparation of a disubstituted phenylboronic acid compound (I) as defined by claim 1 wherein formula (I) R4 is the B(OH) 2 radical, comprising:
a) bromination of methyl 4-bromo-3-methylbenzoate into the compound (1):
b) substituting the bromine atom introduced in step a) by an alkyl radical R5 having from 1 to 4 carbon atoms to obtain a compound (2):
c) converting the ester function of the intermediate (2) or of methyl 4-bromo-3-methylbenzoate into a tertiary alcohol function by reaction with an organomagnesium compound of formula R2-MgX wherein X is a halogen and R2 is a methyl, ethyl, propyl or butyl radical, to obtain a compound (3):
d) converting the intermediate (3) into said disubstituted phenylboronic acid compound (I) in the presence of a base and a trialkyl borate, with the proviso that the steps a) and b) are omitted in the event that R1 is a hydrogen atom.
5. A process for the preparation of a disubstituted phenylboronic acid compound as defined by claim 1 wherein formula (I) R4 is the
radical, comprising:
a) bromination of methyl 4-bromo-3-methylbenzoate into the compound (1):
b) substituting the bromine atom introduced in step a) by an alkyl radical R5 having from 1 to 4 carbon atoms to obtain a compound (2):
c) converting the ester function of the intermediate (2) or of methyl 4-bromo-3-methylbenzoate into a tertiary alcohol function by reaction with an organomagnesium compound of formula R2-MgX wherein X is a halogen and R2 is a methyl, ethyl, propyl or butyl radical, to obtain a compound (3):
d) converting the intermediate (3) into an aryl boronate in the presence of a base and a boron tetraalkyl and then into said disubstituted phenylboronic acid compound (I), with the proviso that the steps a) and b) are omitted in the event that R1 is a hydrogen atom.
6. The process as defined by claims 4 or 5 , wherein step a) is carried out in the presence of at least one brominating agent selected from the group consisting of bromine, N-bromosuccinimide, sodium bromate and 1,3-dibromo-5,5-dimethylhydantoin and in a chlorinated or ether solvent.
7. The process as defined by claim 6 , wherein step a) is carried out in the presence of N-bromosuccinimide in dichloromethane.
8. The process as defined by claims 4 or 5 , wherein step a) is carried out in the presence of a free-radical initiator.
9. The process as defined by claims 4 or 5 , wherein step b) is carried out in the presence of an organometallic reagent R′1-M in which M is magnesium, copper or zinc.
10. The process as defined by claim 9 , wherein step b) is carried out in the presence of copper iodide and an organomagnesium compound R′1-MgX in which X is a bromine, chlorine or iodine atom.
11. The process as defined by claims 4 or 5 , wherein step b) is carried out in an ethereal solvent.
12. The process as defined by claims 4 or 5 , wherein step b) is carried out at a temperature of from −40° C. to −20° C.
13. The process as defined by claims 4 or 5 , wherein step c) is carried out in an ethereal solvent at a temperature of from −10° C. to +10° C.
14. The process as defined by claim 4 , wherein step d) is carried out in the presence of an ethereal solvent, a strong base and a trialkyl borate.
15. The process as defined by claim 14 , wherein step d) is carried out in the presence of tetrahydrofuran, butyllithium and triisopropyl borate, at a temperature of from −78° C. to −40° C.
16. The process as defined by claim 5 , wherein step d) is carried out in the presence of a DMF, tetrahydrofuran, DMSO or dioxane solvent, a dichloro [1,1′-ferrocenylbis(diphenylphosphane)]palladium(II) dichloromethane or Pd(dppf)Cl 2 catalyst, a potassium acetate or triethylarnine base, and pinacolborane or pinacoldiborane.