Alkoxy 3- alkyl

Synthetic applications of the asymmetric Birch reduction and reduction-alkylation are reported. Synthetically useful chiral Intermediates have been obtained from chiral 2-alkoxy-, 2-alkyl-, 2-aryl- and 2-trialkylsllyl-benzamides I and the pyrrolobenzodlazeplne-5,ll-diones II. The availability of a wide range of substituents on the precursor benzoic acid derivative, the uniformly high degree of dlastereoselection in the chiral enolate alkylation step, and the opportunity for further development of stereogenic centers by way of olefin addition reactions make this method unusually versatile for the asymmetric synthesis of natural products and related materials. 

Benzoxathiolium salts have proven to be effective masked acylating agents (79S223). 2-Substituted 1,3-benzoxathiolium tetrafluoroborates have now been utilized in the preparation of esters. Reaction of the salt (334) with two equivalents of an alcohol gave the 2-alkoxy-2-alkyl-benzoxathiole (335). Hydrolysis of (335) with red mercury(II) oxide and boron trifluoride etherate in aqueous THF delivered ethyl benzoate in excellent yield (Scheme 72). 

The stereoselectivities in the cleavage of the C—Hg bond with NaBHa depend upon the nature of the radical intermediates and the reaction conditions. Recent attempts to find optimal conditions for this stereoselective cleavage have been published. " The principle is given in Scheme 27 for the oxymercur-ation-demercuration of a,P-unsaturated esters, generating two asymmetric centers in the 3-alkoxy-2-alkyl ester. 

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