Tetrahedron Letters No. 27, PP 2367- 2370, 1978. © Pergamon Press Ltd. Printed in Great Britain. 0040-4039/78/0701-2367#02.00/0 THE STRUCTURE AND ABSOLUTE CONFIGURATION OF CHONDROCOLACTONE, A HALOGENATED MONOTERPENE FROM THE RED ALGA CHONDROCOCCUS HORNEMANNI, AND A REVISED STRUCTURE FOR CHONDROCOLE A Frank X. Woolard and Richard E. Moore Department of Chemistry, University of Hawaii, Honolulu, Hawaii 96822 *i Donna Van Engen and Jon Clardy Ames Laboratory-USDOE and Department of Chemistry, Iowa State University, Ames, Iowa 50011 (Received in USA 28 March 1978; received in lie for publication 4 M~y 1978) In an investigation of volatile compounds from Hawaiian marine algae$ we found that a cyclic halogenated monoterpene, chondrocole A, is a major constituent in the essential oil of a Chondrococcus hornemanni found in the vicinity of the Halona Blowhole, Oahu. From spectral evidence, mainly PMR and mass spectral data, we assigned structure I to chondrocole A. m Further study, however, in particular an X-ray crystallographic analysis of a closely-related metabollte, chondrocolactone (2), has now shown that this structure is incorrect and that chondrocole A has structure 3. ,j 3 R ~~~, 4",R ,d B I 1 RI=CI, R2-Br 2 3 RI-- Br, R2=CI Chondrocolactone (2) was isolated from the CH2CI 2 extract of the alga, using conventional silica gel chromatography (elution with i:i CH2Cl2-hexane), as colorless needles, mp i07-i08 ° 24 (recrystallization from CH2Cl2-hexane) ; [~]D -48 @ (CH2C12, c 0.62). The PMR spectrum of 2 (Table i) was similar to that of 3 except that the signal for the C-2 protons was missing. The presence of an oxo group on C-2 (~,8-unsaturated y-lactone functionality) was indicated by the 2367