## 2 The Phytochemistry of _Artemisia annua_ L. (Qinghao)
### Monoterpenoids
#### 2.5.3 Monocyclic Monoterpenes  
Two unusual cyclopentane monoterepneoids, \(\alpha\)-campholenal ([4501-58-0]) (**284**) [19] and cyclopentene, 4-ethenyl-1,5,5-trimethyl- ([1727-69-1]) (**285**) [23] are reported from _A. annua_. Both are probably derived from cleavage reactions of the corresponding bicyclic monoterepneoids (see Section 2.5.4). 2-Ochtoden-1-al [26532-25-2] (**286**) [25] is another unusual six-membered monoterepene, belonging to the ochtodane class of monoterepneoids (3-ethyl-1,1-dimethylcyclohexane, 9 CI). The vast  
\begin{table}
\begin{tabular}{c c}  & **(273  
majority of monocyclic monoterepenes from _A. annua_, however, are _p_-menthanes (Table 25), incorporating a six-membered ring, which is formed directly by cyclization of an LPP/NPP precursor. \begin{table}
\begin{tabular}{|l|l|l|l|} \hline Name & Alternative Name(s) & CAS number & References \\ \hline _p_-Menth-3-ene (287) & & [500-00-5] & [50] \\ _p_-Mentha-2,4-diene (288) & & [586-68-5] & [25] \\ _q_-Phellandrene (289) & _p_-Mentha-1,5-diene & [99-83-2] & [32] \\ _p_-Phellandrene (290) & _p_-Mentha-1(7),2-diene & [55-10-2] & [22, 25, 45] \\ _q_-Terpinene (291) & _p_-Menthan-1,3-diene & [99-86-5] & [19, 32, 40, 41, 45, 66, 74] \\ \hline \(\gamma\)-Terpinene (292) & _p_-Menthan-1,4,diene & [99-85-4] & [19, 28, 32, 40, 41, 43, 66] \\ \hline Terpinolene (293) & _p_-Mentha-1,4(8)-diene & [586-62-9] & [32, 43] \\ \hline Limonene (294) & _p_-Mentha-1,8-diene & [138-86-3] & [24, 31, 34, 43, 45, 50, 66, 111] \\ \hline _p_-Cyrene (295) & 1-Methyl-4-isopropyl benzene & [99-87-6] & [19, 24, 25, 28, 29, 32, 34, 38, 40, 43, 45, 48, 73, 74] \\ \hline Cuminic alcohol (296) & _p_-Mentha-1,3,5-trien-7-ol & [536-60-7] & [51] \\  & 4-Isopropylbenzyl alcohol & & \\ \hline Cuminal (297) & Cuminaldehyde & [122-03-2] & [23, 25, 32, 43, 45] \\  & _p_-Menthan-1,3,5-trien-1-al & & \\  & _q_-Isopropylbenzaldehyde & & \\ \hline Carvacrol (298) & _p_-Mentha-1,3,5-trien-2-ol & [499-75-2] & [31, 32, 43] \\ \hline Thymol (299) & _p_-Cymen-3-ol & [89-83-8] & [19, 32, 43] \\  & _p_-Mentha-1,3,5-trien-3-ol & & \\ \hline _p_-Cymen-8-ol (300) & 2-(4-Methylphenyl)-2-propanol & [1197-01-9] & [19, 25, 32] \\ \hline Menthol (301) & _p_-Menthan-3-ol & [89-78-1] & [23, 25, 30, 60, 111] \\ \hline \hline \(\beta\)-Terpineol (302) & _p_-Menth-8-en-1-ol & [7299-41-4] & [43] \\ _cis-p_-Menth-2-en-1-ol (303) & & [29803-81-4] & [19, 45] \\ _trans-p_-Menth-2-en-1-ol (304) & & [29803-82-5] & [19, 45] \\ \hline _p_-Menth-2,8-dien-1-ol (305) & 1-Methyl-4-(1-methylylethyl)-2-cyclohex-1-ol & [3886-78-0] & [32] \\ \hline _trans_-Carveol (306) & _p_-Mentha-1,8-dien-6-ol, _trans_- & [1197-07-5] & [19, 25, 41, 43, 45] \\ \hline _cis_-Carveol (307) & _p_-Mentha-1,8-dien-6-ol, _cis-_ & [1197-06-4] & [19, 41, 43] \\ \hline _trans_-Carvyl acetate (308) & _p_-Mentha-6,8-dien-2-ol, acetate, _trans_- & [1134-95-8] & [19, 31] \\ \hline _cis_-Carvyl acetate (309) & _p_-Mentha-6,8-dien-2-ol, acetate, _cis-_- & [1205-42-1] & [19] \\ \hline Carvone (310) & _p_-Mentha-1,8-dien-6-one & [99-49-0] & [19, 24, 25, 28, 32, 43] \\ \hline _p_-Mentha-1(7),5-dien-2-ol (311) & & [30681-15-3] & [43] \\ \hline _p_-Mentha-1(7),8-dien-2-ol (312) & & [35907-10-9] & [51] \\ \hline _p_-Mentha-1-en-5-ol (313) & & [55708-42-4] & [22] \\ \hline _p_-Mentha-1,4(8)-dien-3-ol (314) & & [6753-08-8] & [32] \\ 3-Cyclohexene-1-methanol 2-hydroxy- & & [138913-54-9] & [25] \\ \(q\),n,4-trimethyl-1, 1-acetate (315) & & [491-07-6] & [45] \\ \hline _iso_-methone (316) & _p_-Mentha-1-en-3-one & [89-81-6] & [24] \\ \hline Piperientone (317) & _p_-Menth-1-en-4-ol & [562-74-3] & [19, 30, 31, 32, 34, 41, 43, 45, 51, 66] \\ \hline \end{tabular}
\end{table} 
Table 25: _p_-Menthane Monoterpenoids, 8 CI (1-Methyl-4-(1-methylylethyl)cyclohexane, 9 CI). **Table 25.**_Cont._