Question

Are any reagents needed for a 1,2-hydride or 1,2-alkyl shift?

Answer 1

If not, how do they occur?

Answer 2

They occur mostly under acidic conditions (though not always, see bottom of page) and not necessarily by means of a single reagent. They occur due to the formation of unstable carbocation intermediates that rearrange to yield more thermodynamically stable products.

http://chem.libretexts.org/Textbook_Maps/Organic_Chemistry_Textbook_Maps/Map%3A_Organic_Chemistry_With_a_Biological_Emphasis_(Soderberg)/15%3A_Electrophilic_reactions/15.07%3A_Carbocation_rearrangements