CA Civ Code Section 3386

Notwithstanding that the agreed counterperformance is not or would not have been specifically enforceable, specific performance may be compelled if:

(a)

Specific performance would otherwise be an appropriate remedy; and

(b)

The agreed counterperformance has been substantially performed or its concurrent or future performance is assured or, if the court deems necessary, can be secured to the satisfaction of the court.