The instant claim for contribution is based upon allegations of breach of duty that were previously raised by plaintiff, and rejected on the merits, in a legal malpractice action litigated by the parties in Supreme Court, Westchester County. Plaintiff is thus collaterally estopped from relitigating her essential breach of duty claims ( see Ryan v. New York Tel., 62 NY2d 494, 500). Moreover, inasmuch as this action and the prior action are premised on the identical underlying transactions, the unappealed dismissal on the merits of the prior action is entitled to res judicata effect with respect to the instant action ( see O'Brien v. City of Syracuse, 54 NY2d 353, 357; Barrett v. Kasco Constr. Co., Inc., 84 AD2d 555, affd 56 NY2d 830).