Ring expansions, three atom

Three atom ring-expansion of cyclopropenyl azides and diazo-compounds provides a useful route to triazines and pyridazines respectively 278). 

A palladium-catalyzed three-component reaction with 2-iodobenzoyl chloride or methyl 2-iodobenzoate, allene and primary aliphatic or aromatic amines to prepare fV-substituted 4-methylene-3,4-dihydro-1 (27/)-isoquinolin-1 -ones was disclosed <02TL2601>. A synthesis of 1-substituted 1,2,3,4-tetrahydroisoquinolines via a Cp2TiMe2-catalyzed, intramolecular hydroamination/cyclization of aminoalkynes was also reported <02TL3715>. Additionally, a palladium-catalyzed one-atom ring expansion of methoxyl allenyl compounds 79 to prepare compounds 80 that can serve as precursors to isoquinolones was reported <02OL455,02SL480>. 

Ring enlargement reactions also take place in 2-oxocycloalkane-l-carbonitri-les substituted in 1-position by an co-alkylester or ketone [17]. The introduction of cyano groups into the a-position of cycloalkanones can be carried out in CH2C12 with C1S02NC0 in dimethylformamide [18]. Two and three carbon atom ring expansion reactions are possible by this method. In most cases the yields are low, which is in contrast with the results of the lactonisation (compare... 

In contrast, three- and four-carbon atom ring expansions proved more successful. Similar results were observed in case of cyclopentanones and cyclohepta-nones [31], and in various heterocyclic systems (N, O, S) [32]. 

The cation radical 88 is obtained in low yield by the reaction of thietane with hydroxy radicals. A three-electron bond between the two sulfur atoms was proposed. The ring-expansion of thietanes to 1,2-dithianes by treatment with elemental sulfur will be discussed in Section II.5.K. 

Cyclopropylcycloalkanones (38) undergo three-atom photochemical ring expansion into a mixture of trans and cis cyclonon-4-enones 39 and 40 (equation 29) . 

Table 4. Mean values of the expansion coefficients for the CH2, NH, and C—C groups in three-atom rings...

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