Diene synthesis regiocontrolled

Dehalogenation 246, 412 Dehydration 56 Dehydrohalogenation 246 Deoxygenation 26 Dialkylamine melhylation 148 Diazo reaction 128,313 Diene synthesis 40,95,413 Diene synthesis regiocontrolled 86 Diene synthesis steieoeonttoDed 86,281 Oimenzatton 178 Displacement 121,267... 

Highly uMtr-diastereofacial selective cycloaddition of isoprene (2) with 4-isopropyl-2-cyclohexenone allowed a short regiocontrolled and stereocon-trolled synthesis [13] of jS-cadinene and (y2-cadinene, Scheme 3.3). High anti-diastereofacial selectivity also occurs in the Diels-Alder reaction of optically active cyclohexenones 6-9 (Figure 3.2), readily available from the chiral pool, with open chain dienes [14-16]. Their cycloadducts are valuable intermediates in the synthesis of optically active sesquiterpenes in view of the easy conversion of the gem-dimethylcyclopropane and gem-dimethylcyclobutane in a variety of substituents. 

Resorcinols. Condensation of this diene with the ketal of a fi- keto acid derivative results in a resorcinol with complete regiocontrol. Thus, the TiCl4-catalyzed reaction of 1 with ketal ester 2 results in the resorcinol 3 in 72% yield. However, use of the acid chloride 4 corresponding to 2 in the same reaction results in the isomeric resorcinol, methyl olivetolate (5). The regiocontrol is based on the reactiv ity order acid chloride > ketal > ester. The resorcinol 5 was used in a biomimetic synthesis of the chromene A1 -tetrahydrocannabinol (6), a component of marijuana. 

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