N.Y. Real Prop. Law § 267
A conveyance of, or charge on, an estate or interest in real property, containing a provision for the revocation, determination or alteration of the estate or interest, or any part thereof, at the will of the grantor, is void, as against subsequent purchasers and incumbrancers, from the grantor, for a valuable consideration, of any estate or interest so liable to be revoked or determined, although the same be not expressly revoked, determined or altered by the grantor, by virtue of the power reserved or expressed in the prior conveyance or charge. Where a power to revoke a conveyance of real property or the rents and profits thereof, and to reconvey the same, is given to any person, other than the grantor in such conveyance, and such person thereafter conveys the same real property, rents or profits to a purchaser or incumbrancer for a valuable consideration, such subsequent conveyance is valid, in the same manner and to the same extent as if the power of revocation were recited therein, and the intent to revoke the former conveyance expressly declared. If a conveyance to a purchaser or incumbrancer, under this section, be made before the person making it is entitled to execute his power of revocation, it is nevertheless valid, from the time the power of revocation actually vests in such person, in the same manner, and to the same extent, as if then made.
N.Y. Real Prop. Law § 267