Syntheses s. a. Diene

Sydnones s. Isosydnones Syntheses (s. a. Diene syntheses, Friedel-Crafts -)... 

The method has been applied in asymmetric and regioselective syntheses of several natural compounds. Two simple examples are the commercial syntheses of the gipsy moth hydrophobic sex attractant, disparlure (RE. Rossiter, 1981, 1985) and < mono-epoxidation of a diene in a leukotriene B4 synthesis (L.S. Mills, 1983). 

The [(s-trans-diene)ZrCp2] complex (s-trans-1) equilibrates with the [(s-cA-diene)ZrCp2] isomer (x-cA-l) via a reactive high lying (r 2-butadiene) metallocene intermediate (2) [A(s-trans-1 s-cis-l, 283 K) = 22.7 0.3 kcal mol-1]. Syntheses of the (butadiene)zirconocene system carried out under kinetic control invariably led to pure s-trans-1, whereas a ca. 1 1 equilibrium of s-trans-1 and. v-ci.v-l was obtained under conditions of thermodynamic control.5,6 The cr,7i-structured s-cis-l isomer undergoes a dynamic ring-flip automerization process (see Scheme 2) that is rapid on the NMR time scale [AG futom = 12.6 0.5 kcal mol ].5... 

Green has also used the method of H+ addition to a -CHO-substituted (allyl)metal complex for the preparation of (s-trans-diene) complex derivatives of a Group 8 metal. The Ru complex 35 was synthesized in that way.33 Stable [(s-tra ,s-r 4-conjugated diene) Ru(acac)2] isomers have been described34 and related [(s-tra s-r 4-diene)Ru(trispyrazolylbo-rate)Cl] systems are stable and isolable.35 Eventually, Mashima et al. have described the reaction of all-tra ,s-l,8-diphenyloctatetraene with [Ru(acac)3] under reducing conditions. A dimetallic complex (36) was isolated and characterized by X-ray diffraction, that contained a linear array of two (s-tra ,s-r 4-diene)Ru subunits36 (see Scheme 10). 

Previous syntheses of tricarbonyl( /-diene)iron complexes have relied mainly on the reaction of Fe(CO)s, Fc3(CO)i2, or Fc2(CO)9 with the free diene. The use of the first two carbonyls suffers from the prolonged reflux times and/or ultraviolet irradiation necessary to obtain reaction and the consequent low yields and mixtures of complexes obtained with heat- and ultraviolet-sensitive dienes. The latter reagent, although utilized at lower temperatures, may react with polyenes (n > 3) to give mixtures containing, in addition to the expected product, binuclear derivatives containing a metal—metal bond.2... 

The complex functions as a convenient source of the tricarbonyliron moiety by displacement of the unsaturated ketone. For example, reaction with 1,3-cycloheptadiene results in a 78% yield of (//-l,3-cycloheptadiene)tricar-bonyliron. More importantly, it may be used in syntheses of tricarbonyl-(diene)iron complexes where the iron carbonyls are not satisfactory. Several complexes of sensitive heptafulvenes have been prepared in this way, and the reagent has been used in the synthesis of tricarbonyliron complexes of several steroids. 

Only two reports have appeared on the formation and properties of linear unsaturated polycarbostannanes and this is a fruitful area for continued study. Such materials have been synthesized by acylic diene metathesis (ACDMET) of bis(4-pentenyl)dibutyltin either with Schrock s Mo-alkylidene, Mo(=CHMe2Ph)( A-2,6-C6H3 - i -Pr2)(OCMe(CF3 )2)2, or with the aryloxo-tungsten catalyst W(0)Cl2(0-2,6-C6H3-Br2)2, Equation 3.8.8). ... 

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