Piperidine formation

New cyclizations via photochemically generated aminyl radicals have been reported, including further examples of the Hofmann-Loeffler-Freytag reaction.313 Intramolecular addition of an aminyl radical, generated by photochemically induced nitrogen chlorine bond homoysis, is also accompanied by cyclization as illustrated by the conversion of the unsaturated N-chloroamide 378 to the pyrrolidine 379.314 Piperidine formation can also... 

Another form of olefin metathesis widely used for piperidine formation is ring-rearrangement metathesis (RRM), as shown below. The versatility of this reaction can be seen in its ability... 

A second sample of DNA is treated with a piperidine-formate buffer of pH 2 in the cold. This promotes the acid depurination of both guanine and adenosine. 

Give an explanation for this stereochemical outcome of piperidine formation. 

The combination of palladium(II) catalysts with stoichiometric amounts of cop-per(I I) salts as oxidants allowed the subsequent development of further diamination reactions. A particularly attractive approach to cychc guanidines 144 from easily accessible precursors 143 was realized within such a diamination reaction of alkenes (Scheme 16.38) [SK)]. It is interesting to note that the reaction proceeds already with copper(II) dichloride and with unprecedentedly enhanced rates also for piperidine formation. The selection of carbamate protecting groups readily provides the free guanidinium products within a single-step transformation. 

A similar approach was used for intramolecular aminofluorination of unactivated olefins mediated by the chiral hypervalent iodine(III) reagent 40 leading to the enantioselective formation of fluorinated piperidine ring derivatives (Scheme 18) [63]. Reagent 40 performs the aminofluorination of pentenamines showing total regioselective control for the 6-endo cyclization products in favour of piperidine formation in excellent enantiomeric excesses (up to 81% ee, 99% ee after recrystallization). 

G G -t A C + T C A > C DMS- Acid Hydrazine- Hydrazine- ( + 1.5 M NaCl) NaOH Piperidine Acid Piperidine Piperidine Piperidine Piperidine Piperidine formate Piperidine Piperidine Hperidine... 

Depurination reaction with 0.13 M aqueous piperidine formate at pH 2.0, 20°C, and for 60 min. The depurination is followed by strand scission in the presence of piperidine. 

Sherman ES, Fuller PH, Kasi D, Chemler Sr., Pyrrolidine and piperidine formation via copper (II) carboxylate-pro-moted intramolecular carboamination of unactivated olefins diastereoselectivity and mechanism. J. Org. Chem. 2007 72 (10) 3896-3905. 

The piperidine formation reaction has been applied for the total synthesis of allopumiliotoxine 267A [82]. 

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