Pyranoid enones

Carbohydrate Dienophiles. The most popular carbohydrate dienophiles to date have been pyranoid enones. Examples of Diels-Alder reactions involving carbohydrate 2,3-enones, 3,4-enones, and enolone esters are described below. In landmark studies reported by Fraser-Reid and co-workers, carbohydrate-derived 2,3-enones were shown to react with dienes to give cyclohexopyranosides (7- 3), Derivatives of methyl and ethyl 2,3-dideoxy- a D-g/ycero-hex-2-enopyranosid-4-ulose 1 underwent cycloaddition with butadiene in the presence of aluminum chloride, and with oxygen -substituted dienes in the absence of any catalyst. Annulated pyranosides 2 and 3 were obtained... 

The effect of high pressure on cycloaddition reactions involving carbohydrates as substrates has been extensively investigated by Jurczak and coworkers (6-S). In their studies of Diels-Alder reactions of pyranoid enones, improvements in stereoselectivity were observed when the reactions were carried out at high pressure (6). 

Photochemical cycloadditions have been among the least widely studied cycloaddition reactions of carbohydrate derivatives, however, some noteworthy examples have been described in the earlier as well as more recent lierature.. Photoannulations of pyranoid enones with both vinyl acetate and ethylene have been described by Fraser-Reid, Hicks, and Primeau 49). Cycloaddition of vinyl acetate to 86 gave the cyclobutano pyranoside 87 as a mixture of diastereomers. This reaction was explored as an approach to the asymmetric synthesis of the insect pheromone grandisol. 

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