Is it permissible for the wealthy to avoid paying zakat on their profits from projects and properties by investing them in new projects before the year is complete?

There is no harm in moving money around, but for a merchant, the dropping of zakat depends on the type of assets. Assets not intended for sale, like hotels, are not subject to zakat. However, raw materials and goods in shops are trade assets, and zakat is obligatory on them. Their zakat cycle is not interrupted by their purchase. If a Muslim buys an asset for personal use (qinyah) to escape zakat, the zakat obligation does not drop, and he will be punished with the opposite of his intention.