2.3- dimethyl-4-carboxylic acid, ring

Ring cleavage of l-oxo-l,2,3,4-tetrahydro-jS-carboline derivatives (374) may be accomplished by base-catalyzed hydrolysis to yield tryptamine-2-carboxylic acids (375). In the case of the 1,9-dimethyl derivative decarboxylation accompanied acid-catalyzed ring-opening, and the corresponding tryptamine (376) was obtained directly. 

Notable examples of general synthetic procedures in Volume 47 include the synthesis of aromatic aldehydes (from dichloro-methyl methyl ether), aliphatic aldehydes (from alkyl halides and trimethylamine oxide and by oxidation of alcohols using dimethyl sulfoxide, dicyclohexylcarbodiimide, and pyridinum trifluoro-acetate the latter method is particularly useful since the conditions are so mild), carbethoxycycloalkanones (from sodium hydride, diethyl carbonate, and the cycloalkanone), m-dialkylbenzenes (from the />-isomer by isomerization with hydrogen fluoride and boron trifluoride), and the deamination of amines (by conversion to the nitrosoamide and thermolysis to the ester). Other general methods are represented by the synthesis of 1 J-difluoroolefins (from sodium chlorodifluoroacetate, triphenyl phosphine, and an aldehyde or ketone), the nitration of aromatic rings (with ni-tronium tetrafluoroborate), the reductive methylation of aromatic nitro compounds (with formaldehyde and hydrogen), the synthesis of dialkyl ketones (from carboxylic acids and iron powder), and the preparation of 1-substituted cyclopropanols (from the condensation of a 1,3-dichloro-2-propanol derivative and ethyl-... 

The A -acyl derivatives of 4-substituted-3,4,5,6-tetrahydro-27/-l,3-oxazin-2-ones proved to behave as effective chiral auxiliaries in asymmetric enolate alkylations and aldol reactions, the stereoselectivities of which were found to be higher for 4-isopropyl than for 4-phenyl derivatives <2006OBC2753>. The transformations of 4-isopropyl-6,6-dimethyl-3-propa-noyl-3,4,5,6-tetrahydro-2/7-l,3-oxazin-2-one 251 to 252 or 253 proceeded with excellent diastereoselectivities (Scheme 47). 6,6-Dimethyl substitution within the oxazine ring facilitated exclusive exocyclic cleavage upon hydrolysis of the C-alkylated and the aldol products 252 and 253, to furnish a-substituted carboxylic acids 254 or a-methyl-/ -hydroxycarboxylic acids 256. 

More recently [31] the same authors reported the synthesis of Co(OMTPC)PPh3 via self-condensation of 3,4-dimethyl-2-(a-hydroxybenzyl)-pyrrole-5-carboxylic acid. The procedure represents the first example of direct formation of the corrole ring from a monopyrrolic precursor. 

The construction of a thieno[3,2-Z>]pyridine by pathway M involves the successive formation of the N(l)-C(2) and C(3)-C(4) bonds of the pyridine fragment. Various 3-aminothiophene-2-carboxylic acid derivatives are most often used as the starting reagents with 2C-components, which introduce carbon atoms C(2) and C(3) into the pyridine ring. For example, the reaction of amino ester 155 with dimethyl acetylenedicarboxylate (156) involves intramolecular cyclocondensation followed by hydrazinolysis to give derivatives of the new heterocyclic system thieno[2, 3 5,6] pyrido[2,3-<7]pyridazine (157) (1991JHC205, 1990SPH203). 

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