Aldehydes cyclization

A further application of ring-closing metathesis in seven-membered heterocyclic ring formation is in the synthesis of the trans-fused oxpane systems. This process involved tandem RCM/allylstannane-aldehyde cyclizations and interaction of the process provides access to trans-fused polyoxepanes <00S883>. 

A new synthesis of dibenzo[a,g]quinolizinium derivatives also makes use of an aldehyde cyclization (Scheme 80) (75JAP(K)7596599). In one example, a benzyl bromide bearing an acetal-masked aldehyde group in the ortho position (126) was allowed to react with the anion (127) generated by the action of phenyllithium on a Reissert compound. The condensation product was heated with alkali to cleave the benzoyl and cyano groups to yield the isoquinoline (128), then the acetal was cleaved and the resulting aldehyde cyclized to (129), presumably under acid conditions. 

M. C. McIntosh and S. M. Weinreb, A strategy for synthesis of conduritols and related cyclitols via stereodivergent vinylsilane-aldehyde cyclizations, J. Org. Chem. 56 5010 (1991). 

Azomethine imines can cycloadd to an internal C—C triple bond producing new bicyclic pyrazoline systems. Thus, imine (161), prepared in situ from the corresponding aldehyde, cyclized to a tricyclic pyrazoline (Scheme 50).78 ... 

Other activated methylene compounds have been used in the aldehyde cyclizations as well.8-11 Aminopyridines containing an alkoxycarbonyl... 

Tandem RCM/allylstannane-aldehyde cyclizations are successfully used for the iterative synthesis of /ra/w-fused oxepane systems, particularly, three tricycles modeling different fragments in brevetoxins and ciguatoxins <2000S883>. Grubbs catalyst <1996JA100> was used on RCM step of the tandem while the procedure similar to that proposed by Yamamoto et al. <1991TL7069> was applied on the second step. 

Diene/aldehyde cyclization. Ene-type reaction is induced by Ni(cod)2-Pli3P in THE at room temperature. 

Aminocinnamonitriles may be obtained from benzaldimines by a palladium-mediated reaction with acrylonitrile these are then cyclized (without purification) by heating in mesitylene. When acrylonitrile is replaced by styrene, and mercury(II) oxide added (to oxidize the imine group to the aldehyde), cyclization gives 3-phenylisoquinolin-l-ones in good yield. 

The (2,4-dinitrophenyl)osazone (15) is oxidized by periodate, consuming 2 moles per mole and liberating formaldehyde and another aldehyde. This second aldehyde cyclizes to give a crystalline compound, probably a pyrazole or dihydropyridazine. Color reactions and the chromatography of the osazone are discussed in Section VI (see p. 199). 

Benzo[h] thiophene undergoes selective Rieche formylation (65%) in the 3-position with dichloromethyl butyl ether and TiCl4.508 2-Bromo- and 3-methylbenzo[h]thiophene are similarly formylated in the vacant thiophene position.345 508 The diarylmethane compounds 121 (Ar = thiophene, benzo-[h]thiophene, or benzene) undergo Rieche formylation, but the resulting aldehyde cyclizes under the conditions of the reaction, to give the annelated products 122.509... 

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