Piperidine, structure

Chart 1. Experimental reactivity diagrams from piperidino-dehalogenation. Rates relative to a given position (= 1). Reactions in piperidine, structures 25-28 in alcohol, structures 29-31. Data deduced from refs. 18, 20, 29, 42, 43 and 98. 

Piperidine. Structure, Preparation, Reactivity, and Synthetic Applications of Piperidine and its Derivatives by M. Rubiralta, E. Glralt and A. Diez... 

Phenothiazine antipsychotics can be divided in the aliphatic phenothiazines with a dimethylamino-propyl group, those with a piperazine structure and agents with a piperidine structure. 

Undoubtedly, the two main areas of interest and controversy in this general area are (i) tautomerism, particularly in the vinylogous amides 2- and 4-pyridinone and related compounds, and (ii) the question of conformation in piperidine structures. 

Similarly, fV-BOC-aminoalcohols can be subjected to Mitsunobu reaction conditions to yield the piperidine structure 10 (Equation 26) <2004JOC2229>, which is an intermediate in the synthesis of galactohomonojirimycin (BOC = /-butoxycarbonyl). Cyclization of an iV-BOC derivative of an aminoalcohol mesylate was reported in the synthesis of enantiopure 3-hydroxy-4-phenylpiperidine derivatives starting from L-phenylglycine <2004TL987>. 

Although a number of alkaloids belonging to the simple arylquinolizidine class and the lactonic type had been synthesized, no successful synthesis of cyclophane alkaloids was accomplished until that of lythranidine (94), a unique alkaloid with a 2,6-trans disubstituted piperidine structure, was reported (28, 29). Quinolizidine metacyclophane alkaloids lythrancepines II (95) and III (96) have also been synthesized recently (30, 31). A review on the synthesis of lythranidine (94) is available in Japanese (32). 

The biomimetic construction of piperidine skeletons from N-methylhomoallyl-amines is performed by means of the ruthenium-catalyzed oxidation and subsequent olefm-iminium ion cyclization reaction. trans-l-Phenyl-3-propyl-4-chloropiper-idine 57 ivas obtained from N-methyl-N-(3-heptenyl)aniline stereoselectively via 56 upon treatment ivith a 2 N HCI solution (Eq. 3.72). This cyclization is the first demonstration of biomimetic formation of piperidine structure using N-methyl group, and can be rationalized by assuming the formation of iminium ion 58 by protonation of the oxidation product 56, subsequent elimination of f-BuOOH, nucleophilic attack of an alkene, giving a carbonium ion, which is trapped with Cl nucleophile from the less hindered side. 

Of all the photostabilizers now in commercial use, those based on the hindered piperidine structure have attracted the most interest. On the commercial front, several workers have shown how effectively photostabilizers operate in a polymer, and in one article Karrer has described in considerable detail methods of their preparation. On the scientific front there has been considerable activity into their mode of operation. It is now well established that these hindered-piperidine stabilizers operate through a radical scavenging mechanism to produce a substituted hydroxyalmine, as in Scheme 32. 

The ability of these energy quenchers to stabilize polypropylene fibers to weathering permitted the development of many new end-uses, but their capabilities have been surpassed by a new group of stabilizers that contain a hindered piperidine structure. As shown above, these HALS compounds can be very good long-term thermal stabilizers. Hindered piperidines react with hydroperoxides during polypropylene processing to form nitroxyl radicals (II) that arc effective polymer radical traps [134]. These nitroxyl radicals react with polymer free radicals to form the polymeric hydroxylamine (III). 

Coniine, a-propylpiperidine, is found in spotted hemlock— Conium maculatum (Apiaceae). It is a piperidine structure with a short ahphatic side chain, and is a volatile oily compound. Coniine is very toxic and causes death by paralysis. 

Conhydrine is an alkaloid having a hydroxylated piperidine structure that is present in many natural products and therapeutics. This oxygenated alkaloid was isolated from the seeds and leaves of hemlock Conium maculatum Asymmetric hydrogenation of ketone rac-116 was performed in i-PrOH by using catalyst Ru[(5)-Xyl-SDP][(R, R)-DPEN] Cl2 (5a,R,R)-113b) at S/C= 10,000 to give (—)-a-conhydrine in 96% yield with 97% ee and 91 9 anti-... 

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