Corporate transformations can take on different forms. Which of the following is not one of the common approaches mentioned as imposing duties on the board?

The option involving private transfers of immaterial quantities of publicly-traded stock on a stock exchange is not typically considered a common approach that imposes specific duties on the board. Corporate transformations often involve significant changes in company structure or strategy, which typically triggers a heightened level of scrutiny and responsibility for the board of directors.

On the other hand, sales of subsidiaries, mergers and acquisitions, and restructuring for financial stability are all substantial events that involve the board taking on significant duties. These processes require the board to make strategic decisions, assess risks, and act in the best interests of shareholders, which underlines their fiduciary responsibilities. In contrast, private transfers of small amounts of stock do not represent the same level of corporate transformation or impact, hence, the board's responsibilities in such situations are less pronounced.