3- Amino-4-chromanone

Chromanone, 3-acetamido-2-methyl-reduction, 3, 729 Chromanone, 3-amino-synthesis, 3, 734 Chromanone, 3-arylidene-thermoisomerization, 3, 722 Chromanone, 3-benzylidene-thermolysis, 3, 728 Chromanone, 3-bromo-2-hydroxy-benzofuran from, 3, 729 Chromanone, 6,8-dimethyl-hydroxymethylation, 3, 731 Chromanone, 2,3-epoxy-as synthon, 3, 735... 

A typical second step after the insertion of CO into aryl or alkenyl-Pd(II) compounds is the addition to alkenes [148]. However, allenes can also be used (as shown in the following examples) where a it-allyl-r 3-Pd-complex is formed as an intermediate which undergoes a nucleophilic substitution. Thus, Alper and coworkers [148], as well as Grigg and coworkers [149], described a Pd-catalyzed transformation of o-iodophenols and o-iodoanilines with allenes in the presence of CO. Reaction of 6/1-310 or 6/1-311 with 6/1-312 in the presence of Pd° under a CO atmosphere (1 atm) led to the chromanones 6/1-314 and quinolones 6/1-315, respectively, via the Jt-allyl-r 3-Pd-complex 6/1-313 (Scheme 6/1.82). The enones obtained can be transformed by a Michael addition with amines, followed by reduction to give y-amino alcohols. Quinolones and chromanones are of interest due to their pronounced biological activity as antibacterials [150], antifungals [151] and neurotrophic factors [152]. 

Macrocyclic derivatives of type 361 (Fig. 142) can be prqyared from bis-Mannich bases of diketones and o-phenylenediamines, as the replacement of both the amino groups of the base takes place instead of the expeeted cyclization involving the earbonyl groups. Seven-membered ring compounds having canccrostatic properties, such as 362, are similarly derived by condensation of the Mannich ba.scs of chromanone. ... 

Monoacyl-type protecting groups are not recommendable for N -protection, since racemi-zation of the related amino acid derivatives during carboxy activation for their coupling represents a serious problem. Consequently, Ai-acyl derivatives such as formyl or tri-fluoroacetyl have been used mainly for side-chain protection. Nevertheless, some new N -derivatives, which address this problem, have been proposed. With the quinone-derived acyl-type protecting group 3-methyl-3-(2,4,4-trimethyl-3,6-dioxocyclohexa-l,4-dienyl)butyryl (74) (Scheme 39) racemization is almost totally suppressed, and it is readily cleaved with sodium dithionite with formation of the chromanone byproduct The Al -(alkyldisulfa-... 

The palladium-catalyzed deprotection and E D P was then applied to the synthesis of 3-substituted 4-chromanones from cyclic P-keto esters 51 [29]. Among the amino alcohols tested, cinchonine 43 led to optically active chromanone 52 with a moderate 22% ee (Scheme 7.23), far from the enantioselectivity induced by aminoborneol (60% ee). 

With some conformationally less mobile substrates such as those in Eq. (38), ee values up to 82% and high diastereoselectivity, characterize the use of the N-pro-tected amino acid-ligated rhodium(II) catalysts for chromanone formation [56, 57]. 

Following the synthesis of chroman-3-ones from salicylaldehydes by reaction with acrylonitrile and subsequent hydrolysis and a Curtius reaction, their behaviour towards the protected p-amino ketone 51 has been studied. Both 5- and 8-methoxychromanones afforded 57/-benzopyrano[3,4-6]pyridines whereas other chromanones gave spirocyclic aminochromans <04S121>. 

Other different chiral carbene catalysts have been developed by other authors and tested specifically in intramolecular Stetter reactions (Scheme 6.10). This is the case of menthol-derived thiazolium salt 121 ° and tripeptide 122 incorporating a thiazolylalanine amino acid as constituents, which were used as pre-catalysts in the same reaction shown in Schemes 6.3 and 6.4 leading to chromanones. However, these two new catalytic systems, although active and able to promote rather efficiently the reaction, only furnished moderate levels of enantioselection. In a different approach, a C2-symmetric imidazoli-dinium salt 123 has been employed to generate the corresponding catalytically active carbene species and employed in the cyclization of 7-oxo-2-pentenoates leading to chiral cyclopentenones. In this case, this intramolecular Stetter reaction proceeded with moderate to good yields and enantioselectivities up to 80% ee. 

Methoxy 3- [a-hydroxylainino-veratry 1]-chromanon-(4) oxim oder 3 Hydroxyl amino 7-methoxy 3>veratxyl-onroma non (4)-oxim 18 ll 493. 

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