He met in secret in 1991, I think in June, with his Belarusian and and Ukrainian counterparts and decided to break up the Union (I don't know the details and don't think anybody does, except the people concerned).
The pan-Union vote on whether or not to preserve the Union -- the yeas making up 70% of the vote, the Baltics abstaining, was in September.
The abortive coup to throw Gorbachev from power was in August. There is some speculation that Gorbachev himself was behind the coup, that it was mainly really a show of force to scare Yeltsin into behaving, and that Yeltsin realized this and used it to whip up public fears of a return to Stalinism.
The CPSU voted to dismantle the USSR -- 85% voting in favor of discarding it, including Zyuganov -- was I believe in November. (Note how glaringly this contrasts with the popular vote.)
According to Gorbachev, the Yeltsinites were deliberately aggravating the economic situation -- for instance, they had given orders to food tranports not to bring produce into Moscow.
How these events should be linked together, I don't know.
Chris Doss The Russia Journal