UPDATE 1-Behind the scenes of Sanofi's boardroom bust up
* Board votes unanimously to remove CEO Viehbacher
* Relations had deteriorated between chairman, CEO
* Tensions fired up around mature products review
* Viehbacher wanted free hand to steer company (Recasts with eviction of CEO, Weinberg quotes, background)
By Natalie Huet and Noëlle Mennella
PARIS, Oct 29 (Reuters) - A boardroom tussle brewing for months at Sanofi came to a head on Wednesday when France's top drugmaker fired its chief executive, wiping more billions off its share price.
While the showdown played out in leaks to national newspapers has stunned investors as a "how not to do it" guide to corporate governance, the writing was on the wall in the deteriorating relationship between Chairman Serge Weinberg and CEO Chris Viehbacher.
The decision, which will see Weinberg take the helm until a new CEO is found, follows a dramatic few days during which Viehbacher had to present quarterly results without being able to reassure investors of his board's support.
Instead, German-Canadian Viehbacher told Reuters on Tuesday that Weinberg had declined to clarify his future at a meeting the previous day, confirming reports of increasingly frosty relations between the CEO and the rest of the board. Continuación...