Process for preparing 4-substituted piperidines

A process for preparing a compound of formula I:

• 31
• wherein Pg represents a suitable nitrogen protecting group;
• X represents a heterocycle, substituted heterocycle, substituted alkenyl or substituted aryl wherein the substituted heterocycle, substituted alkenyl or substituted aryl are substituted with from 1 to 3 suitable activating groups;
• and
• R1, R2, R3, R4, R5, R6, R7, and R8 each independently represent an alkyl, alkenyl, cycloalkyl, aryl, substituted aryl, heterocycle, or substituted heterocycle, comprising treating a compound of formula II:
• 32
• wherein the substituents are defined as above, with triethylsilane and trifluoroacetic acid.

A process for preparing a compound of formula Ia:

• 33
• wherein X represents a heterocycle, substituted heterocycle, substituted alkenyl or substituted aryl wherein the substituted heterocycle, substituted alkenyl or substituted aryl are substituted with from 1 to 3 suitable activating groups;
• and
• R1, R2, R3, R4, R5, R6, R7, and R8 each independently represent an alkyl, alkenyl, cycloalkyl, aryl, substituted aryl, heterocycle, or substituted heterocycle, comprising treating a compound of formula II:
• 34
• wherein Pg represents a suitable nitrogen protecting group and the remaining substituents are defined as above, with triethylsilane and excess trifluoroacetic acid.