Ring synthesis 1.2.3.4- tetrahydro-1 -methyl

The ring synthesis of the tetrahydro-1,3-azoles is simply the formation of N,N-, N,0-or A, S-analogues of aldehyde cyclic acetals the ring synthesis of the 4,5-dihydro-heterocycles requires an acid oxidation level in place of aldehyde. A good route to the aromatic systems is therefore the dehydrogenation of these reduced and partially reduced systems. Nickel peroxide, " manganese(IV) oxide, copper(II) bromide/ base, and bromotrichloromethane/diazabicycloundecane have been used. The example shown uses cysteine methyl ester with a chiral aldehyde to form the tetrahydrothiazole. 

Lumazine, 1,3,6,7,8-pentamethyl-5,6,7,8-tetrahydro-rearrangement, 3, 308 Lumazine, 5,6,7,8-tetrahydro-autoxidation, 3, 308 oxidation, 3, 306 Lumazine, 1,3,6,7-tetramethyl-ring transformations, 3, 308 Lumazine, 1,3,5,6-tetramethyl-5,6,7,8-tetrahydro-synthesis, 3, 316 Lumazine, 2-thio-reactions, 3, 300 sulfurization, 3, 296 Lumazine, 4-thio-methylation, 3, 299 reactions, 3, 300 Lumazine, 1,3,7-trimethyl-acylation, 3, 290 Lumazine, 1,6,7-trimethyl-bromination, 3, 302 synthesis, 3, 295 Lumazine, 3,6,7-trimethyl-... 

Thiazole, 4-methyl-5-(2-hydroxyethyl)-in thiamine biosynthesis, 1, 97 Thiazole, 4-methyl-2-methylami nosynthesis, 6, 300 Thiazole, 4-methyl-2-phenyl-alkylation, 6, 256 mercuration, 6, 256 Thiazole, 2-(methylthio)-methylation, 6, 290 thermodynamic values, 6, 291 Thiazole, 2-methylthio-5-phenyl-synthesis, 5, 153 Thiazole, 4-methyl-5-vinyl-occurrence, 6, 327 Thiazole, 2-phenyl-acetylation, 6, 270-271 Conformation, 6, 237 synthesis, 5, 113, 6, 306 Thiazole, 4-phenyl-conformation, 6, 237 2,5-disubstituted synthesis, 6, 304 Thiazole, 5-phenyl-conformation, 6, 237 Thiazole, 2-phenyl-5-triphenylmethyl-synthesis, 6, 265 Thiazole, 2-(2-pyridyl)-metal complexes, 5, 51 6, 253 Thiazole, 4-(2-pyridyl)-metal complexes, S, 51 6, 253 Thiazole, tetrahydro-ring cleavage, 5, 80 Thiazole, 2,4,5-trimethyl-occurrence, 6, 327... 

A variety of l,2,3,4-tetrahydro-j8-carbolines have been prepared from 3-piperidone phenylhydrazone derivatives. Used initially to obtain pentacyclic derivatives (35) related to the yohimbe alkaloids, this route was later extended to the synthesis of tetracyclic compounds (36). l-Methyl-5,6,7,8-tetrahydro-j8-carboline (37) was prepared in low yield by heating cyclohexanone 2-methyl-3-pyridylhydrazone with zinc chloride, a synthesis probably based on the similar preparation of the tetracyclic compound 38 starting from the corresponding quinolylhydrazine. Abramovitch and Adams extended this approach to the cyclization of cyclohexanone 3-pyri-dylhydrazone (39) itself. The main product was 6,7,8,9-tetrahydro-8-carboline (40), a smaller amount of the j8-isomer (41) also being obtained. This provides a convenient and readily reproducible route to the otherwise difficultly accessible 8-carboline ring system. The favored attack at carbon-2 over carbon-4 of the pyridine nucleus... 

The cycloadducts formed from the Diels-Alder reaction of 3-amino-5-chloro-2(17/)-pyrazinones with methyl acrylate in toluene are subject to two alternative modes of ring transformation yielding either methyl 6-cyano-l,2-dihydro-2-oxo-4-pyridinecarboxylates or the corresponding 3-amino-6-cyano-l,2,5,6-tetrahydro-2-oxo-4-pyridinecarboxylates. From the latter compounds, 3-amino-2-pyridones can be generated through subsequent loss of HCN <96 JOC(61)304>. Synthesis of 3-spirocyclopropane-4-pyridone and furo[2,3-c]pyridine derivatives can be achieved by the thermal rearrangement of nitrone and nitrile oxide cycloadducts of bicyclopropylidene <96JCX (61)1665>. 

Hydrolytic reactions can also be applied in the synthesis of aldehydes or ketones via the corresponding 1,3-oxazine derivatives. The anion formed from 3-methyl-2-(4-pyridyl)tetrahydro-l,3-oxazine 155 on treatment with BuLi proved to react with various electrophiles (alkyl halides, carboxylic esters, acid chlorides, or aldehydes) exclusively at position 2 of the 1,3-oxazine ring and not at the pyridine nitrogen atom. The readily formed 2,2-disubstituted-l,3-oxazine... 

The synthesis of a new series of tetrahydro-oxazolo[4,5-d]-1,2,3-triazoles (102) has been reported. The triazolium imide 1,3-dipole (104) reacted with ( )-cinnamaldehyde in refluxing ethyl methyl ketone. It is significant that it was to the C=0 bond of the a,/ -unsaturated aldehyde that the cycloaddition took place, yet analogous addition to benzaldehyde or aliphatic ketones was not possible. The primary products of the cycloaddition reaction (105) underwent a sigmatropic rearrangement to furnish the new ring system (102) as shown in Scheme 23 <90JCS(P1)2527>. 

A partial synthesis of burnamicine (131) from geissoschizine methyl ether (130) takes advantage of the c/D ring cleavage of tetrahydro-/3-carbolines by means of ethyl chloroformate (Scheme 13),79 which simultaneously introduces a function into position 3, thereby facilitating the formation of the 3-oxo-substituent. An exactly analogous route was used for the synthesis of 19,20-dihydroburnamicine (133) from hirsutine (132). 

The cycloadducts of cyclooctatetraene and its substituted derivatives with 4-phenyl- and 4-methyl-37/-triazole-3,5(4//)-dione and diethyl diazenedicarboxylate are intermediates in the synthesis of polycyclic structures5 10 l2 23. Furthermore, pyrolysis of the diethyl diazenedicarboxylate cycloadduct 12 affords diethyl 1.2.4a,8a-tetrahydro-l,2-cinnolinedicarboxylate with undetermined stereochemistry of the ring fusion23. 

In CHEC-II(1996), there are two reactions involving the synthesis of 2,3-dihydro-l//-l,3-diboroles by transformation of other rings <1996CHEC-II(3)767>. One of these reactions involves thermal ring contraction of 1,4,5,6-tetra-methyl-l,2,3,4-tetrahydro-l,4-diborinine 66 at 160°C to 4,5-diethyl-l,2,3-trimethyl-2,3-dihydro-l//-l,3-diborole 67. Uhm heated a solution of compound 66 in toluene in a pressure tube at the same temperature and obtained 1,2,3,4,5-pentamethyl-2,3-dihydro-l//-l,3-diborole 68 (Scheme 11) <2005JKC329>. 

The first representative of ring system Type III was obtained by Sorrentino during the synthesis of 1,2,3,5-tetrahydro-3//-l,4-benzodiazepines. Ring expansion of 2-halomethyl-1 -methyl-4-phenyl-1,2,3,4-tetrahydroquinazo-lines to 1,4-benzodiazepines involves the formation of azirino[2, l-6]quina-zolines of type 30. This step is followed by cleavage of the C—N bond of the aziridine ring by the action of sodium borohydride. 

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