This invention provides compounds of Formula I, methods for their preparation and use for preparing compounds of Formula II wherein R1, R2, R3, R5, R6, X and n are as defined in the disclosure. This invention also discloses preparation of compounds of Formula III wherein R1, R2, R7, R8, R9 and n are as defined in the disclosure. This invention also pertains to certain compounds of Formula 4 and 6 used to prepare compounds of Formula I. wherein R1, R2, R5, X and n are as defined in the disclosure.