Hydrazones intermolecular reactions

In a combination of photochemical cyclization and a radical reaction Yoshimatsu et al synthesized 2-azabicyclo[33.0locta-3,7-diene 169 from the trienal hydrazone 166.1891 The domino process was initiated by irradiation of 166 at 400-500 nm in benzene. The transformation may include an intermolecular [2+2]-cyclization, followed by ring opening to give... 

Intermolecular coupling between ketones and 0-methyl oximes, hydrazones and nitrones is achieved on reduction at a tin cathode in isopropanol [105]. It is not clear which of the reacting species accepts the initial electron in these processes. The reaction with 0-methyloximes, followed by catalytic reduction of the first formed O-methylhydroxylamine, is a convenient synthetic route to 2-amino-alcohols. 

In contrast to the hydrazones mentioned above, a,/ -unsaturated N -sulfonyl imines react as electron-deficient diene component in aza Diels-Alder reactions. In addition to several investigations dealing with their intermolecular cycloadditions under thermal and under high pressure conditions [231-234], Boger s... 

Similarly to the asymmetric synthesis by imines and oxazoline, there is also a chiral hydrazone, (S)-l-amino-2-(methoxymethyl)pyrrolidine 51a, which gives chiral hydra-zones on reaction with aldehydes and ketones104, and is able to form an intermolecular chelate with the methoxy group. Enders and coworkers used this system for enantioselec-tive aldol reaction105, and for synthesis of chiral ketone104 and aldehyde106 (equation 30). 

Intermolecular alkyl radical addition to imine derivatives was studied in aqueous media using indium as a single electron transfer radical initiator. The one-pot reaction based on radical addition to glyoxylic hydrazone provided a convenient method for preparing the a-amino acids. Indium-mediated radical addition to an electron-deficient C=C bond also proceeded effectively to provide a new carbon-carbon bond-forming method in aqueous media (Scheme 7.11).15... 

PhI(OTf)2 is an effective oxidant for the direct formation of bicyclic diazenium salts from a variety of linear hydrazone precursors. This oxidative cyclization is postulated to occur by the iodine(III)-mediated formation of an l-aza-2-azoniaallene salt intermediate. A direct intermolecular allylic amination has been achieved with up to 99% yields using metal-free conditions. The reaction employs a hypervalent iodine(lll) reagent as an oxidant and bistosylimide as a nitrogen source. Mechanistic studies including isotope labelling and Hammett correlation indicated that depending... 

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