This paper discusses the discovery of uncommon taste or trigeminal active compounds and their associated sensory analysis using human tasting panels with the aim of enhancing the overall taste experience whilst reducing where possible the sugar and salt content of foods. The first example outlines the discovery of the sensory quality attributes of (R)-2-(carboxymethylamino)propanoic acid, named (R)-strombine, as assessed by a panel of 47 subjects to confirm its contribution to the typical taste of scallop muscle. The second example discusses the pungency and trigeminal effect of polygodial, which is compared with piperine and capsaicin, as well as the elucidation of a new structure eliciting a trigeminal effect, (+/-)-trans-2,3,3a,7a-tetrahydro-1 H-indene-4-carbaldehyde, discovered in Amomum tsao-ko. Finally, the time intensity trigeminal effect of (-)-menthol is compared with (1R,2RS,4RS)-1-isopropyl-4-methylbicyclo[3.1.0]hexan-2-ol, named dihydroumbellulol, a new cooling compound obtained by hemi-synthesis from umbellulone extracted from Umbellularia californica Nutt.

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The cycloadditions of met hoxydehydrobenzenes containing a 3met hoxy group and 3met hoxyfuran are highly regioselective. The adducts, 1,4-dihydro-2-methoxy-1,4-epoxynaphthalenes, undergo mild acid-catalysed hydrolysis providing, first, an isolable 1,2,3,4-tetrahydro-2-methoxy-1,4-epoxynaphthalen-2-01, and then a 3,4-dihydro-l,4-epoxynaphthalen-2(1 H ) -o n e . The chemistry of these ketones is explored. One of them, 3,4-dihydro-5-methoxy-l,4-epoxynaphthalen-2( 1 H ) -one, readily undergoes catalytic reduction t o yield the hexahydro-l,4-epoxynaphthalene-2,5( 1 H,4aH)dione. The X-ray molecular structure of this dione and of the 2-monobrosyl ester of the derived diol are reported. Treatment of the above adducts with trifluoroacetic acid and acetic anhydride provides a convenient synthesis of 1 -acetoxy-2-methoxynaphthalenes.14 could be isolated by fractional crystallization of the crude epoxynaphthalen-2(1H)-one 23 (Scheme 4) (1-H, 6, 5.29 and product. The structural assignment of the hemiacetal 14 is 4-H, 8, 5.88). Therefore the 5-methoxy ketone 15 is that based on its spectral data. The IR spectrum exhibited a band at ketone in which 1-H resonates at 6, 5.01 and 4-H at 6, 5.89. 3370 cm-' attributed to an OH stretching frequency. The ''C and the 8-methoxy ketone 16 is the one in which 1-H resonates NMR spectrum revealed a signal for the methoxy group of the at 6, 5.24 and 4-H at 6, 5.69. in their respective ' H NMR hemiacetal at 6, 50.06, a quaternary carbon atom attributed to spectra. Similar assignments allow distinctions to be made C-2 resonating at 6, 106.39, and the methylene carbon signal between the pairs of ketones 31/32 (Scheme 5), 38/39 (Scheme 6) at 6, 43.02 was attributed to C-3. Nuclear Overhauser effect and 52153 (Scheme 8). (NOE) difference spectroscopy gave evidence for the stereochemistry and the results are shown in Fig. I . Significant interactions are those between the endo-methoxy group at C-2 and both the bridgehead proton 1-H and 3-H,,d,, and between 3-H,,, and the eso-hydroxy group at C-2. Nucleophilic attack by water therefore occurs exclusively from the e.uo-face of the adduct and this mode of attack presumably reflects the unhindered nature of this face of the molecule compared with the endo-face. The spectroscopic properties of the hemiacetal 4 derived from the parent adduct 2 are similar to those of the methoxy derivative 14. In this case the infrared O H stretching 23 9% 19 5% n 39 7% 9 3%* See under section 5.6.

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An economical and practical synthesis of rac‐(Z)‐β‐santalol was accomplished. The key coupling step is based on a Scriabine‐inspired reaction of a dienyl diacetate substrate and an alkene. The total synthesis was achieved in five steps (longest linear sequence) in 19 % overall yield from cyclopentadiene.

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Using titanium tetraisopropoxide, the enantiopure tethered lactaldehyde (α′ S,2S)-2-(3′-hydroxy-α′-methyl-benzyloxy)propanal (6) is cyclized with complete regio- and diastereoselectivity ortho to the phenolic hydroxyl group to give (1S,3S,4R)-3,4-dihydro-1,3-dimethyl-2-benzopyran-4,5-diol (7). Similar cyclization of the epimeric (α′ R,2S)-lactaldehyde (25) yields solely the corresponding (1R,3S,4R)-4,5-diol (34). The 4,5-diacetate (26), but not (35), undergoes conformational inversion of the heterocyclic ring through significant 4,5-peri interactions between the adjacent acetoxy substituents. Spontaneous cyclizations of the corresponding phenoxide ions of the lactalde-hydes (6) and (25), generated by fluoride from their silyl ethers, led to the related 4,7-diols with high regioselectivity through ring-closure para to the aromatic oxygen.

The synthetic challenges associated with the selective synthesis of α-Santalene (1), (Z)-α-Santalol (2), β-Santalene (3), and most importantly (Z)-β-Santalol (4) have interested the world's synthetic chemists for decades. These molecules, lovely examples of nature's exquisite creations, have been isolated from East Indian Sandalwood Oil (Santalum album L.) and have stimulated chemists to develop new and efficient methodologies to synthesize them. The synthesis and evolution of various approaches to the [2.2.1]bicycloheptane ring system present in β-Santalene (3) and the even more challenging selective synthesis of the (Z)-allylic alcohol sidechain present in both (Z)-α-Santalol (2) and ((Z)-β-Santalol (4) will be covered in this review.