Tricyclic sulfur heterocycles

Tricyclic sulfur heterocycles 341 were prepared utilizing an intramolecular [4 + 2] cycloaddition. Heating of allenyl sulfides 340 to 110 °C leads to Diels-Alder products 341 in reasonable yields (Scheme 8.93) [163], Unfortunately, this method does not allow general access to these heterocycles, since a particular substitution pattern of the substrate is required. No reaction occurred with substrates lacking the thioacetal moiety. 

The tricyclic fused heterocyclic system 236 containing a phosphorus atom was constructed by the Diels-Alder reaction. Thus, diazaphospholopyridine 235 was treated with 2,3-dimethylbutadiene in the presence of sulfur or selenium to give the product 236 (Equation 27) <2002JOC9162, 2002T1573, 2005T10521>. 

Plant metabolites that are capable of becoming toxic in sunlight or UVA are produced by a wide variety of biochemical pathways and thus are a structurally diverse group of natural products. Both linear and cyclic photosensitizers are known from plants. Linear phototoxins are generally derived from fatty acid precursors and typically possess conjugated double and triple bond systems. The majority of cyclic photosensitizers, on the other hand, are bi- and tricyclic aromatic molecules that may contain nitrogen, oxygen or sulfur as heterocyclic elements. 

The effect of temperature and stoichiometry on the thiomethylation of hydrazine has been reported <2004RCB1717>. Heterocyclization of hydrazine with an excess of a CH2O-H2S mixture (1 6 4), in the temperature range from 0 to 20 °C, gives the tricyclic 11 and tetracyclic 360 nitrogen-and-sulfur-containing heterocycles. The nature of the product is affected substantially by the reaction temperature. At 20 °C, compound 11 is obtained in 30% yield and 360 in 18% yield. With a ratio of hydrazine CH20 H2S of 1 6 4, and a 0°C reaction temperature, an increased yield of 360 to 31% was observed (Scheme 74). PMR and initio calculations were used to confirm the structures of the products and are discussed further in Sections 9.09.2 and 9.09.3.1. 

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