| 主权项 |
1. A process for the preparation of a compound of formula I, wherein: R1 represents hydrogen, C1-18 alkyl, C2-18 alkenyl, C2-18 alkynyl or C3-18 cycloalkyl, (which latter four groups are optionally substituted by one or more halo atoms) or a suitable hydroxy protecting group; R2 represents hydrogen or C1-18 alkyl, C2-18 alkenyl, C2-18 alkynyl or C3-18 cycloalkyl, (which latter four groups are optionally substituted by one or more halo atoms), or a suitable nitrogen protecting group; and R3 represents hydrogen, —OH, C1-18 alkyl, C1-18 alkoxy, C2-18 alkenyl, C2-18 alkynyl, C3-18 cycloalkyl, (which latter five groups are optionally substituted by one or more halo atoms) or —ORp wherein Rp is a suitable hydroxy protecting group; or which process comprises contacting a compound of formula II, wherein R1a, R2a and R3a are defined according to R1, R2 and R3, respectively, with: (i) a rhodium complex; and (ii) an organic additive selected from the group consisting of: (a) alcohols of formula IIIa, wherein Rx1, Rx2 and Rx3 independently represent hydrogen, a C1-6 alkyl group, a C2-6 alkenyl group, an aryl group or a heteroaryl group (which latter four groups may be optionally substituted by one or more halo atoms or C1-4 alkyl groups); or any two of Rx1, Rx2 and Rx3 are linked together, along with the requisite carbon atom to which they are attached, to form a 4- to 8-membered cyclic alcohol, optionally containing one or more unsaturated bonds within the ring, and which ring is optionally substituted by one or more halo atoms or C1-4 alkyl groups; (b) ketones of formula IIIb, wherein Rx4 and Rx5 independently represent a C1-4 alkyl group, a C2-4 alkenyl group, an aryl group or a heteroaryl group (which four groups may be optionally substituted by one or more halo atoms or C1-4 alkyl groups); or Rx4 and Rx5 are linked together, along with the requisite carbon atom to which they are attached, to form a 4- to 8-membered cyclic ketone, optionally containing one or more unsaturated bonds within the ring, and which ring is optionally substituted by one or more halo atoms or C1-4 alkyl groups; (c) ethers of formula IIIc, wherein Rx6 and Rx7 independently represent a C1-4 alkyl group, or a C2-4 alkenyl group (which groups may be optionally substituted by one or more halo atoms or C1-4 alkyl groups); or Rx6 and Rx7 are linked together, along with the requisite oxygen atom to which they are attached, to form a 4- to 7-membered cyclic ether, optionally containing one or more unsaturated bonds within the ring, and which ring is optionally substituted by one or more halo atoms or C1-4 alkyl groups; and (d) thioethers of formula IIId, wherein Rx8 and Rx9 independently represent a C1-4 alkyl group, or a C2-4 alkenyl group (which groups may be optionally substituted by one or more halo atoms or C1-4 alkyl groups); or Rx8 and Rx9 are linked together, along with the requisite sulfur atom to which they are attached, to form a 4- to 7-membered cyclic thioether, optionally containing one or more unsaturated bonds within the ring, and which ring is optionally substituted by one or more halo atoms or C1-4 alkyl groups. |
