Cyclopropanone selenoacetals

A THF or ethereal solution of selenoacetals derived from aldehydes must be added to n-BuLi or s-BuLi in hexane to avoid side reactions, i. e. their metalation is achieved not by the butyllithium but by the selanylalkyllithium produced in situ [11] (Scheme 10). Moreover, it was observed that selenoacetals formed from aromatic aldehydes and ketones, cyclopropanones are more reactive than those derived from aliphatic carbonyl compounds [11]. The second factor governing the reaction is the steric hindrance around the reactive site. Selenoacetals derived from aldehydes react in a few minutes but those derived from ketones... 

Sulfur and selenium substituents can serve both as the activating group and as the leaving group. Thus, thio- and selenoacetals of aldehydes bearing a leaving group on the jS-carbon atom readily afford cyclopropanone thio- and selenoacetals, respectively. 1,3-Bis (phenylthio) propanes as well as 3-halopropyl sulfides " provide cyclopropyl sulfides... 

The reaction of l-metallo-l,l-bis(seleno)a]kanes with electrophiles is another interesting approach to selenoacetals (Schemes 76 and 77), - which inter alia allows the synthesis of l,l-bis(seleno)cyclo-propanes (Scheme 26, a, b and d Scheme 77, c) and also permits the synthesis of functionalized selenoacetals by concomitant C—C bond formation (Scheme 79). Other methods listed above are of limited use. The substitution of dihaloalkanes by selenolates is the method of choice for the synthesis of bis(seleno)methanes (Scheme 72, a), and can be applied to the synthesis of the relatively unhindered selenoacetal of cyclopropanone (Scheme 72, b). 

Among the a-heterosubstituted cyclopropylmetals a-selenocyclopropyllithiums represent some of the most valuable synthetic intermediates. They are quantitatively prepared from selenoacetals of cyclopropanones and butyllithiums, are thermally stable at------78° for several hours and are parti-... 

Synthesis of 1-Seleno eyclopropyllithiums by Selenium-Metal Exchange from Selenoacetals of Cyclopropanones... 

Scheme 30), and cyclisation to the selenoacetals of cyclopropanones was achieved by treatment with -BuLi in THF (Scheme 30). The carbon-selenium bond of the functionalized orthoester is specifically cleaved at —78 °C but cyclisation of the resulting a-lithio-y-tosyloxy selenoacetal takes place at a higher temperature (between —50 °C and 0 °C). 

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