Friedel-Crafts Acylations 1 he leveling off noted two years ago and the decline last year in the number and variety of Friedel-Crafts acylations seem to have stabilized. The fertile ingenuity of organic chemists continues to provide unique and interesting examples of this important reaction. This reaction class still continues to provide one or more key links in the successful synthesis of complex molecules in such diverse fields as dyes, perfumes, steroids, terpenes. alkaloids, and antibiotics as well as many more directly obvious applications.The tabulation form established in previous reviews is undergoing an experimental test of major importance. The tables with complete lists of references will be provided separately by the editor in photoprint form for those who need them. CatalystsThe importance of polyphosphoric acid as a mild reagent for effecting ringclosure acylations is a significant factor in the appearance of an extensive review of this reagent's utility (60).Zinc oxide is claimed to be a very effective nonhalogen catalyst for aryl acylations (61). Better yields with less undesirable by-products are obtained when nitromethane is included in the reaction medium for acylating phenols and phenol ethers. Tetrachloroethane seemed to be the most desirable solvent (64). Silicon tetraacetate gave only moderate or fair yields of 2-acetylthiophene with stannic chloride, zinc Cilio-. LeROI NELSON is associate professor of organic chemistry at Brigham Young University. He graduated from Utah State Agricultural College and obtained his Ph.D. from Purdue University in 1952. Previous experience includes postdoctoral research at UCLA and teaching at Purdue and Wayne Universities. Nelson is a member of the ACS,