Partially hydrogenated terpenes

Suitable plasticizers include phthalates, phosphates, partially hydrogenated terpenes, adipates, chloroparaffins, castor oil, etc. It is best that the plasticizer does not contain water since it will interfere with the cure of polyurethanes. 

The special potential for constructing double bonds stereoselectively, often necessary in natural material syntheses, makes the Wittig reaction a valuable alternative compared to partial hydrogenation of acetylenes. It is used in the synthesis of carotenoids, fragrance and aroma compounds, terpenes, steroides, hormones, prostaglandins, pheromones, fatty acid derivatives, plant substances, and a variety of other olefinic naturally occurring compounds. Because of the considerable volume of this topic we would like to consider only selected paths of the synthesis of natural compounds in the following sections and to restrict it to reactions of phosphoranes (ylides) only. 

Methylhept-2-en-6-one, usually referred to simply as methylhep-tenone, is a useful synthon for the total synthesis of terpenes. One early synthesis of this intermediate employed the Carroll reaction, the substrate for which is prepared by the addition of acetylene to acetone and subsequent partial hydrogenation to 2-methylbut-3-en-2-ol, as shown in Scheme 4.5. Addition of acetylene to methylheptenone gives dehydrolinalool, which can be hydrogenated to linalool using a Lindlar catalyst. 

QuassMoids). A group of structurally complex tri-terpenes with various tetra- and pentacyclic C -, C -, C20-, and C25-skeleton. The C2o picra ane system is the most widely distributed. Q. occur principally in the wood of the tree Quassia amara indigenous to Brazil and Surinam as well as the Caribbean Picrasma ex-celsa (Simaroubaceae). They have antifeedant effects on insects and taste very bitter. The most important representative of the Q. is quassia (2,12-dimethoxy-picrasa-2,12-diene-1,11,16-trione, nigakilactone D) C22H28O6, Mr 388.46, mp. 221-222 °C, [aJo +34.5° (CHCI3) - a partially hydrogenated phenanthiene derivative. 

The reaction of monodeprotonated [ C2]acetylene with carbonyl compounds has been exploited as a means of extension of the carbon chain of various terpenes and steroids by two [ " C]carbon atoms. In the simplest case, reaction of potassium [ C2]acetylide with steroid ketone 1 and subsequent acid catalyzed cleavage of the enol ether protecting group gave 17a-[ C2]ethynyltestosterone (2). The sequential addition of deprotonated [ C2]acetylene to carbonyl compounds opens access to symmetrical or unsymmetrical [2,3- C2]alkyn-l,4-diols is exemplified in the synthesis of all-tran -/3-[15,15 - C2]-carotene ([ C2]provitamin A). Thus, treatment of lithium [ C2]acetylide with terpene aldehyde 2 followed by double deprotonation of the resultant alkynol 4 and reaction with a second equivalent of 3 provided alkyne-l,4-diol 5 the requisite key intermediate. Subsequent acid-catalyzed dehydration of 5 followed by Lindlar s catalyst-mediated partial hydrogenation and photoisomerization afforded the final product". ... 

Stereoselective reduction of some triazolodiazines (derivatives of ring systems 33 and 37) bearing chiral terpene residues has been elaborated by Groselj el al. <2006TA79>. With catalytic hydrogenation, partial saturation of the six-membered ring was experienced, while reaction with borane-methyl sulfide resulted in formation of triazole-boron complexes. 

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