Synthetic Photochemistry. XXXV. A Synthesis of Bis (dehydroxy) xanthocidin Methyl Ester from the Partially Optical Active Photoisomer of β-Cyclodextrin-included 2-Methoxytropone

A. Mori, Yasuhiro Shimada, H. Takeshita
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Abstract

Starting from the partially-optical active 7-methoxybicyclo[3.2.0]hepta-3,6-dien-2-one, a photoisomer of 2-methoxytropone obtained from the B-cyclodextrin inclusion complex, bis(dehydroxy)xanthocidin methyl ester was synthesized. In 1978, we found2' a photoisomerization of troponoids under a-and P-cyclodextrin (CDX)-included conditions to give bicyclo(3.2.0]hepta-3,6-dien-2-ones with a remarkable rate enhancement and with much improved yields for proto-photoisomers in various dispersion media. The photoproducts derived from tropolone (la) and 2-methoxytropone (lb) were optically active, and by using these optically active specimens, we have carried out a mechanistic investigation of the "antara-antara"-3, 3-sigmatropy;3' the thermolysis of optically active 1-methoxybicyclo[3.2.0]hepta-3,6-dien-2-one (2) to optically active 3-methoxybicyclo[ 3.2.0 ]hepta-3, 6-dien-2-one (3), ruled out an involvement of radical intermediate.`•5•6) Obviously, the photoproduct (2) is good starting material for polysubstituted cyclopentane derivatives, and by this mean we have now synthesized a dialkyl derivative (4) of sarkomycin (B)7' which can be, in same time, designated as a bis(dehydroxyl) derivative of xanthocidin8' from 7-methoxybicyclo[3.2.0Ihepta-3, 6-dien-2-one (5). The findings will be described in this paper. An a-methylenecyclopentanone antibiotic, xanthocidin (A) was first isolated from a Streptomlces species, IVo.51--4by Asahi et al.8' and its racemic form has been synthesized by Smith9' via the key intermediate, bis(dehydroxy)-4, 5-dehydroxanthocidin (C). The above mentioned readines$ in furnishing the cyclopentene synthons prompted us to carry out the experiments on the synthesis of this methylene cyclopentanone relative, methyl ester of bis(dehydroxyl) derivative (4) of A'O' as follows. Prolonged irradiation of lb under the B-CDX-inclusion conditions in cyclohexane afforded optically active 5'i' via the proto-photoisomer (2),i2' 1-methoxyl isomer, in 470/o yield with 550/o enantiomeric excess. Optical activities of these compounds were determined by derivation to 3oxocyclopentaneacetic acid (6). By the Grignard reaction of 5 with isopropylmagnesium bromide and subsequent quenching of the resultant magnesium enolate with methyl iodide, 4-isopropyl-7-methoxy-3-methylbicyclo[3.2.0]hept-6-en-2-one (7) was obtained in 630/o yield in a one-pot operation. The direction of the attack of bulky isopropyl group to the *Department of Molecular Engineering -20Partial Asymmertric Synthesis of Xanthocidin Derivatives from Troponoids
合成光化学。第45。含β-环糊精- 2-甲氧基tropone部分光学活性光异构体合成双(脱氢)黄原苷甲酯
从b -环糊精包合物得到的2-甲氧基tropone的光异构体7-甲氧基双环[3.2.0]庚-3,6-二烯-2- 1开始,合成了双(脱氧基)黄原苷甲酯。1978年,我们发现在含a-和p -环糊精(CDX)的条件下,类troponoids发生了光异构反应,得到了双环(3.2.0)庚-3,6-二烯-2- 1,其速率显著提高,在不同的分散介质中,原光异构体的产率也大大提高。邻苯二酮(la)和2-甲氧基tropone (lb)的光产物具有旋光性,利用这些旋光性样品,我们对“antara-antara”- 3,3 -sigmatropy(3)进行了机理研究;旋光性的1-甲氧基双环[3.2.0]庚-3,6-二烯-2- 1(2)热裂解为旋光性的3-甲氧基双环[3.2.0]庚-3,6-二烯-2- 1(3),排除了自由基中间体的参与。光产物(2)是制备多取代环戊烷衍生物的良好原料,由此我们合成了sarkomycin (B)7'的二烷基衍生物(4),同时可以将其命名为7-甲氧基双环[3.2.0 ihepta3,6 -二烯-2-one(5)]的黄药苷8'的双(去羟基)衍生物(5)。本文将对研究结果进行描述。一种A -亚甲基环戊酮类抗生素黄药(xanthocidin, A)首次从链霉菌IVo中分离得到。51—4由Asahi et al.8'和它的外消旋形式已由Smith9'通过关键中间体,双(脱氢)- 4,5 -去羟基anthocidin (C)合成。上述提供环戊烯合成物的读式促使我们进行实验合成亚甲基环戊酮的近亲,A' o '的双(去羟基)衍生物(4)的甲酯如下。在b - cdx包合条件下,lb在环己烷中长时间辐照,通过原光异构体(2),i2' 1-甲氧基异构体获得了光学活性5'i',产率为470/o,对映体过量为550/o。这些化合物的光学活性是通过衍生得到3oxocypentaneacetic acid(6)来测定的。通过5与异丙基溴化镁的格氏反应,然后用碘化甲基将生成的烯酸镁猝灭,得到4-异丙基-7-甲氧基-3-甲基双环[3.2.0]庚-6-en-2-one(7),收率为630/o。大体积异丙基的攻击方向* *分子工程系-20 -部分不对称合成由troponoid合成的黄原苷衍生物
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