A-Sinensal

The main components are limonene (65-75%) and q-terpinene (16-22%). The characteristic feature of mandarin oil is its content of a-sinensal (0.2-0.5%), methyl A-methylanthranilate (0.3-0.6%, which is responsible for fluorescence), and long-chain unsaturated aliphatic aldehydes [369, 370a, 370d, 370e, 381, 394c, 414-421b]. 

The oils have a high terpene hydrocarbon content (>90%, mainly (+)-limonene), but their content of oxygen-containing compounds differs and affects their quality. Important for aroma are aldehydes, mainly decanal and citral, and aliphatic and terpenoid esters. The sesquiterpene aldehydes a-sinensal [17909-77-2] and/3-sinensal [6066-88-8], which contribute particularly to the special sweet orange aroma, also occur in other citrus oils, although in lower concentration [369-370a, 370d, 394,421, 430-438]. 

Scheme 23.13 Biocatalytic-chemocatalytic reaction sequence to produce a-sinensal from trans-nerolidol. 1 Aspergillus niger sp., Aspergillus niger ATCC 9142, Rhodococcus rubropertinctus DSM 43197 2 chemical conversion steps...

Trans P-sinensal 441 is obtained from the aldehyde 438 prepared by selective ozonolysis of trans-famesene 437. Wittig olefmation of 438 with 1-formylethylidene-phosphorane 440 gives trans P-sinensal 441. Reaction of 438 with 1-ethoxycarbonyl-ethylidene-triphenylphosphorane 439 yields the ethyl ester 442, from which 441 can also be obtained 237 (Scheme 77). Furthermore, a working group of the BASF synthesized a-sinensal 443 and p-sinensal 441 using Wittig reactions 238). 

BUchi has used Mander s approach as a key step in his synthesis of a-sinensal (212 Scheme 50), and Corey has applied the ylidic 3,2-rearrangement to the efficient preparation of 3-cyclopentenones. Thus, base treatment of the sulfonium salt (213) first gave the rearranged product (215). Thermal vinylcyclo-propane ring expansion then produced the spiro compound (216). Deprotection finally gave the noncon-jugated cyclopentenone (217 Scheme 51). 

Italian mandarin oils are characterised by the terpenes limonene (app. 70%) and y-terpinene (app. 20%). Apart from a-sinensal and long-chain saturated aldehydes there is a number of sensorially important unsaturated aldehydes with citrus-like, aldehy-dic, fatty and waxy flavour. Also the potent C-11-hydrocarbons (l,3E,5Z)-undeca-triene, (1,3E,5E,8Z)-, (l,3E,5Z,8Z)-undecatetraene and methyl N-methylanthranilate characterise the typical taste and odour of red mandarin [76]. The latter compound, which also causes the fluorescent character of mandarin oil, is a main constituent of mandarin leaf oils (see Petitgrain oils). 

When compared to Italian mandarin oils, other mandarin [77] or tangerine oils such as Dancy [76] or Murcott tangerine [78] are even more dominated by limonene (app. 95%). Moreover, the composition of the flavour compounds and, therefore, the entire flavour profile, is considerably less complex [76], This is also evident in the rather different content of methyl N-methylanthranilate and a-sinensal. Apart from the... 

The aim of this book is to show you how this planning is done to help you learn the disconnection or synthon approach to organic synthesis. This approach is analytical we start with the molecule we want to make the target molecule) and break it down by a series of disconnections into possible starting materials. In the last chapter of the book we shall discuss the synthesis of the natural product a-sinensal (1) and we shall devise a route using five different, easily available starting materials (2-7). 

No-one could look at the structure of a-sinensal and immediately write down the five starting materials. We arrive at these only after a prolonged analysis with many disconnections. This book shows you the systematic... 

ISO standard 3528 shows character and data for this oil. a Sinensal is a marker for mandarin essential oil. Adulteration is made by synthetic methyl n metl l anthranilate, as well as methyl anthra-nilate. Orange terpenes and limonene (80°), dipentene, citronellal, and citral are used for blending. Detection is done by GC-MS but improved results show multidimensional chiral separation. Dugo and Mondello (2011) reported the following chiral data (5) (+) a-thujene (0.3%-1.9%) (/ )-(-)-a thujene (98.1%-99.7%) (/ )-(+)-a pinene (41.7% 54.5%) (S)-(-)-a-pinene (45.5-58.3) ... 

Hydroxy-frani-nerolidol (472a) is an important precursor in the synthesis of interesting avor of a-sinensal. Hrdlicka et al. (2004) reported the biotransformation of trans- (469) and CM-nerolidol (462) and cis-/trans-mixture of nerolidol using repeated batch culture of A. niger grown in... 

The aldehydes a-sinensal and p-sinensal with a veiy low odor threshold occur as minor compounds in essential oils from various Citrus species. 

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