Carbonyl, addition lithio reagent

The carbanions of 1-alkenyl sulphoxides 400 also react with carbonyl compounds to give the corresponding condensation products384 (equation 237). Solladie and Moine have used this type of reaction in their enantiospecific synthesis of the chroman ring of a-tocopherol 401. Addition of the lithio reagent 402 to the aldehyde 403 affords the allylic alcohol 404 in 75% yield as a sole diastereoisomer481 (equation 238). 

A marked improvement on what amounted to pyrolysis consists in treatment of the dienone with strong base. In the case at hand, the carbonyl group at position 17 needs to be protected against attack by the lithio reagent. The ketone at position 17 is therefore first converted to its trimethylenedioxy acetal 2-7 by reaction with propylene-1,3-diol in the presence of a small amount of acid. Treatment of this l,4-dien-3-one with lithium metal in the presence of diphenylmethane leads to the trimethylenedioxy acetal, 2-9, of estrone. The diphenylmethane present in the reaction mixture presumably quenches the extruded methyllithium to prevent its addition to the starting dienone. Treatment with dilute acid then restores the carbonyl group to afford estrone (1-2). 

The lithio derivative (97) can be used as both a formyl and carboxyl acyl anion equivalent, and this species undergoes conjugate addition to a,6-unsaturated carbonyl groups to give 1,4-adducts in good yield. This versatile reagent has also been used to prepare a-hydroxy aldehydes and ketones. 

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