In an article (photo of relevant portion) that appeared in the Middle East Journal in 1987 entitled The New Iranian Left, Nozar Alaolmolki explains how it happened:
...the leftists were able to mobilize more than half-a-million supporters and sympathizers for the May Day rally in Tehran alone. This trend continued during the next few months until the Islamic Republic consolidated itself and then turned against the leftists. The Tudeh Party was spared initially, but by 1983 all leftist organizations, including the Tudeh, were banned and a large number of their active members executed, imprisoned, forced underground or otherwise eliminated from the scene.Ironically, before his overthrow, the Shah fled to Egypt.
Fast forward to 2011 and the only differences between the situation between Iran and Egypt have to do with the brand of Islam behind the revolution, the name of the two countries' respective leaders, and geography. The uprising in that country is backed by the Muslim Brotherhood, which has the support of the left. Specifically, the Obama administration and the likes of Bill Ayers, Bernadine Dohrn, and Code Pink, were all instrumental in forming the Free Gaza Movement, a group allied with the Muslim Brotherhood and Hamas.
For as intellectual as Ayers, Dohrn, and the rest of the elite leftwing in the United States who either support or act as apologists for Muslim Brotherhood-linked groups like CAIR like to be portrayed, they sure are stupid.
Go HERE for more on the Iranian Revolution.