3714
bromic acid at 100" for 2 hr, followed by work-up, gave added in 15 min under a nitrogen atmosphere at 55". 3,5-dimethyl-2-cyclopentenone10in 83 yield. In a After stirring for 3 hr the mixture was neutralized with similar manner IIb was converted to 2-methyl-2-cyclodilute hydrochloric acid and then worked up. Distillapentenone (IIIb)" in 44% yield. When IIc was extion at 120-125" (5 mm) gave the adduct IId (806 mg, posed to this acidic condition, the resulting product 60%). Successively alcohol IId (476 mg, 2 mmol) was proved to be 3-butyl-2-methyl-2-cyclopentenone ( I I I C ) ~ ~mixed ~ ~ with 47 hydrobromic acid (3 ml) and heated at ( 5 6 z yield), and none of the corresponding posi100" for 9 hr. Work-up and tlc purification (silica gel, tion isomer, 2-amyl-2-cyclopentenone, was detected. ether-hexane (3 : l), R f = 0.7) gave dihydroisojasmone It should be noted that the original methyl group is not (IIId) (196 mg, 5973, bp 130" (bath temperature) (3 incorporated into the five membered ring and a long mm). alkyl side chain resides at the 3-position. Accordingly The present simple procedure coupled with the selecdihydroisojasmone (IIId)12 was obtained from IId tive dichlorocarbene addition possesses wide applicabil(59% yield). Acid treatment of alcohol IIe resulted in ity. Extention of this reaction is being explored. the formation of 2-methyl-3-propenyl-2-cy~lopentenone~ Acknowledgment. We thank Dr. Hisashi Yamamoto ( 7 0 z yield). Under this acidic condition the anticifor helpful discussions. pated isoallethrone (IIIe) isomerized to more thermodynamically stable conjugated dienone. Finally the Tamejiro Hiyama,* Masao Tsukanaka, Hitosi Nozaki sequence was used to prepare 2,3-decamethylene-2Department of Industrial Chemistry, Kyoto Unicersity Yosliidu, Kyoto, 606 Japan cyclopentenone (IIIf), a versatile intermediate of pyridoReceiued March 2, 1974 muscone, l 3 muscone, l 4 and [ lO]metacyclophane synthesis. l 5 From 2-cyclododecylidene ethanol (If) the enone IIIf was obtained in 37 overall yield. The mechanism of the cyclopentenone formation, Structure of Bacteriochlorophyll b1 which is not clear yet, can be rationalized by the following scheme. Conjugate dehydration of I1 gives IV,16 Sir : which easily ionizes to yield the pentadienyl cation V. Bacteriochlorophyll b (Bchl b)* is the principal green Thermal conrotatory ring closure17 of V produces the pigment of the photosynthetic bacterium Rhodopseucyclopentenyl cation. Deprotonation, l 6 followed by domonas viridis. The electron excitation spectrum of hydrolysis of the resulting chlorodiene, produces 111.l8 Bchl b is similar to but even more strongly red shifted than that of the bacteriochlorophyll a (Bchl a), 1. It enables this bacterium t o use light down to 9800 cm-I (1020 nm), the least energetic light used by any known photosynthetic organism. The close structural relationship between Bchl a and b was established by Iv V Brockmann and Kleber,4 who converted both to 2desvinyl-2-acetylpyromethylpheophorbide a5 and esA typical experiment is illustrated by the preparation tablished Mg as the central metal and phytol as the of dihydroisojasmone. To a solution of 3-methyl-2esterifying alcohol. The most distinct difference benonenol (Id) (880 mg, 5.64 mmol) and cetyltrimethyltween Bchl a and b is the easy conversion of the latter ammonium bromide (50 mg) in chloroform (3 ml), into products related to chlorophyll a (Chl a), which aqueous sodium hydroxide (1.5 g in 1.5 ml of water) was corresponds formally to oxidation of the macrocycle (IO) The primary product may be the isomer IIIa, which is, however, from the tetrahydro- to the dihydroporphyrin level. recorded to isomerize to the obtained compounds under acidic condiAs cis chlorins are easily oxidized to porphyrins and tions: I. N. Nazarov and A. N. Elizarova, Otd. Khim. Nauk, 295 (1951); Chem. Abstr., 46,914h (1952). show a red-shifted visible absorption spectrum com(11) H. N. AI-Jallo and E. S. Waight, J. Chem. SOC.E, 73 (1966). pared to the corresponding trans epimers,6 Brockmann4 (12) A. L. Voitsekhovskaya, N. A. Kosul'nikova, 'I, A. Rudol'fi, V. M. Dashunin, and V. N. Belov, Zh. Vses. Khim. Obshchest., 10, 702 in 1970 formulated Bchl b as the 3,4-cis epimer of Bchl (1965); Chem. Abstr., 64, 9588a (1966); A. L. Voitsekhovskaya, N. A. a (structure 2). Kosul'nikova, T. A. Rudol'fi, R. I. Sharapova, V. M. Dashunin, and At the end of the same year, Baumgarten7 proposed V. N. Belov, Zh. Org. Khim., 3, 18 (1967); Chem. Abstr., 66, 9 4 7 1 2 ~ (1967). structure 3 for Bchl b, which formulates Bchl b as the (13) I
