Enantioselective process
View Patent ↗An enantioselective process for preparing intermediates useful in the preparation of the chiral tricyclic compound of formula I is disclosed.
1. A process for the preparation of a compound represented by formula V
which comprises (1) contacting a compound represented by formula IIA
with at least about an equivalent amount of phosphorous acid in the presence of catalytic amount of an alkali iodide or iodine and hydrobromic acid in water to form a reaction mixture, and then adding to the reaction mixture at least about an equivalent of hypophosphorous acid to form a compound represented by formula IIIA
(2) contacting the resulting compound represented by formula IIIA with at least about an equivalent amount of bromine in the presence of an organic acid and a lower alkanol to form a compound represented by formula IVA
2. The process of claim 1 which further comprises the step of contracting the compound represented by formula IVA with at least about equivalent amount of hypophosphorous acid and the presence of sodium nitrite in a aqueous acidic medium to form the compound represented by formula V
3. The process of claim 1 wherein a mixture a compound of IIA and a compound represented by formula IIB:
is present in the contacting step (1) and a compound represented by formula IVB
is also formed in step (2).
4. A process of preparing compounds represented by formulas IVA and IVB
which comprises contacting compounds represented by formulas IIA and IIB
with at least about an equivalent amount of phosphorous acid in the presence of at least a catalytic amount of sodium iodide, hydrobromic acid, in water to form a reaction mixture and adding to the so-formed reaction mixture at least about an equivalent amount of hypophosphorous acid, and continuing the contacting for a time sufficient to form a reaction mixture comprising the compounds represented by formulas IIIA and IIIB, and contacting the resulting reaction mixture with at least about an equivalent of bromine in the presence of an organic acid and a lower alkanol to form a compound represented by formula form a mixture comprising the compounds represented by formulas IVA and IVB.