Piperidinone oxidation

Piperidin-4-one N-oxide, 2,2,6,6-tetramethyl-solvent effects, 2, 146 Piperidinones stability, 2, 159-161 synthesis, 2, 81, 95 from S-aminopentanoic acids, 2, 402 Piperidin-2-ones IR spectroscopy, 2, 130 synthesis... 

A novel one-pot tandem oxidation-cyclization-oxidation process was successfully applied in the transformation of unsaturated alcohols 250 [Eq. (5.315)].860 The intermediate aldehyde formed by oxidation with pyridinium chlorochromate (PCC) undergoes a carbonyl-ene cyclization followed by an additional oxidation to form 3-substituted piperidinones. 

The kinetics of the oxidation of piperidinone thiosemicarbazones by chloramine-T have been studied in acetic/perchloric acid media.95... 

Oxidation of piperidinone thiosemicarbazones with chloramine-T (CAT) is first order in CAT and fractional order in the substrate. The reaction showed an inverse fractional order dependence on acidity. A plausible mechanism has been indicated 98 Kinetics of oxidation of -propylamine and n-bulylaminc by CAT and chloramine-B (CAB) have been determined and mechanisms have been proposed.99 Mechanisms have been proposed and rate laws derived for the oxidation of dimethylglyoxime100 and p-crcsol101 with CAT. 

Primary amines form Schiff bases, (CH )2C=NR. Ammonia induces an aldol condensation followed by 1,4-addition of ammonia to produce diacetone amine (from mesityl oxide), 4-amino-4-methyl-2-pentanone [625-04-7], (CH3)2C(NH2)CH2COCH3, and triacetone amine (from phorone), 2,2,6,6-tetramethyl-4-piperidinone [826-36-8]. Hydroxylamine forms the oxime and hydrazine compounds (RNHNHJ form hydrazones (RNHN=C(CH3)2). Acetone and nitrous acid give the isonitroso compound which is the monoxime of pymvaldehyde [306-44-5], CH COCH=NOH. 

A more economical use of 40, in terms of carbon atoms and chiral centers, was devised to produce the heteroyohimbine alkaloid ajmalicine and its 19-epimer [54]. As shown in Scheme 11.13, deoxygenation of 40 at C6 followed by oxidative cleavage of the vinyl group gave the corresponding aldehyde 43, which was equilibrated to the equatorial isomer 44. Subsequent reaction with tryptamine gave the piperidinone 45. Bisher-Napieralsky cyclization provided the alkaloid skeleton, which was elaborated to ajmalicine 46. 

Both enantiomers of 272 were synthesized from (V-methyl-4-piperidinone and 1,3,5-trimethoxybenzene [604], The 3 -hydroxyl was introduced with hydroboration of an alkene and then inversion via oxidation to the ketone and NaBH4 reduction. Introduction of the chromone moiety via acylation of the phenyl ring, followed by O-demethylation, provided 272 [604]. Subsequently, additional analogs of 272 were synthesized and tested for biological activity [609]. 

Chiral hydrazones derived from SAMP or RAMP are used in the asymmetric synthesis of 4,5,6-trisubstituted and 6-substituted piperidinones <97LA1115>. Chiral 2-substituted piperidines are prepared by the addition of Grignard reagents to chiral imines followed by oxidation of the terminal double bond and reductive cyclization <97JOC746>. 

This section deals with oxidation reactions as an initiative step of the domino process in combination with many other organic transformations. In 2004, Snaith and coworkers [3] demonstrated a simple and efficient method to synthesize 3-substituted 4-piperidinones 4 using a domino oxidation/carbonyl-ene/oxidation reaction (Scheme 9.1). This domino reaction comprises oxidation of unsaturated alcohol 1 using PCC (pyridinium chlorochromate) to give the corresponding aldehyde 2, followed by a carbonyl-ene type reaction to yield the secondary cyclic alcohol 3, which was oxidized under the reaction conditions to give 3-substituted 4-piperidinones 4 in good yields. 

Quantum mechanical studies of the mechanism of gold-catalysed rearrangements of acetylenic amine-A -oxides to piperidinones or azepanones show a concerted 1,5 hydrogen shift (Scheme 112). ... 

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