Patent ID: 7674922

Claim:
A process for preparation of a product compound of the formula: wherein: R 1 is H, substituted or unsubstituted alkyl, carboxylic ester, or acyl; R 2 is H, OH, protected hydroxyl, substituted or unsubstituted alkyl, alkenyl, alkynyl, acyl, aryl, or heteroaryl; R 3 is H, substituted or unsubstituted alkyl, carboxylic ester, or acyl; and R 4 is H, substituted or unsubstituted alkyl, silyl, hetero-substituted or unsubstituted acyl, alkylsulfonyl, arylsulfonyl, alkylphosphoryl, or arylphosphoryl; said process comprising: treating a first intermediate compound of the formula: with an organoaluminum-based Lewis acid catalyst, under conditions effective to produce the product compound.