Alkenes from acetates

It is possible to prepare 1-acetoxy-4-chloro-2-alkenes from conjugated dienes with high selectivity. In the presence of stoichiometric amounts of LiOAc and LiCl, l-acetoxy-4-chloro-2-hutene (358) is obtained from butadiene[307], and cw-l-acetoxy-4-chloro-2-cyclohexene (360) is obtained from 1.3-cyclohexa-diene with 99% selectivity[308]. Neither the 1.4-dichloride nor 1.4-diacetate is formed. Good stereocontrol is also observed with acyclic diene.s[309]. The chloride and acetoxy groups have different reactivities. The Pd-catalyzed selective displacement of the chloride in 358 with diethylamine gives 359 without attacking allylic acetate, and the chloride in 360 is displaced with malonate with retention of the stereochemistry to give 361, while the uncatalyzed reaction affords the inversion product 362. 

Table 3. Preparation of 2-Chloro-l,l,l trifIuorO 2-alkenes from Aldehydes, Zinc, and Acetic Anhydride [63]...

Normally, the dominant products are the alkene and acetate ester, which arise from the carbocation intermediate by, respectively, elimination of a proton and capture of an acetate ion.269... 

Alkenes from vie -diols.2 The 2-dimethylamino-l,3-dioxolanes 1, obtained by reaction of a 1,2-diol with N,N-dimethylformamide dimethyl acetal in quantitative yield, when treated with ethyldiisopropylamine (4 equiv.) and triflic anhy-... 

Hydrogenation using Raney nickel is carried out under mild conditions and gives cis alkenes from internal alkynes in yields ranging from 50 to 100% [356, 357, 358, 359, 360]. Half hydrogenation of alkynes was also achieved over nickel prepared by reduction of nickel acetate with sodium borohydride (P-2 nickel, nickel boride) [349,361,362] or by reduction with sodium hydride [49], or by reduction of nickel bromide with potassium-graphite [363]. Other catalysts are palladium on charcoal [364], on barium sulfate [365, 366], on... 

O 16.14% crysts (from acet, benz or ethyl acetate), mp 206.5-07.5° 214.5-15.5°, de-pending on cryst size, rate of heating solv used fairly sol in hot benz CCI4 diffc sol in eth, acet, eth acet acet ac insol in ale was obtd by ozonolysis of 1,1-diphenyl-l-alkenes In CCI4 and hydrolysis of the ozonide No expin of this compd occurred when heated to its mp, but when heated for 5 mins at 214-15°, it decompd comjietely to benzo-phenone... 

This subject has recently been reviewed.647 Several additional papers have appeared on the catalytic oxidation of alkenes by 02 in the presence of PdCl(MeCN)2N02(148).64S Terminal alkenes and trans- cyclooctene yield the corresponding ketones, cyclopentene and cyclohexene the corresponding allyl alcohol, and bicyclic alkenes the corresponding epoxide. Heterometallacy-clopentanes such as (152) have been isolated from the reaction of (148) with norbornene (dicy-clopentadiene), and characterized by X-ray crystallography.6486 Glycol monoacetates were obtained from the reaction of (148) with terminal alkenes in acetic acid.649... 

Homer-Wadsworth-Emmons reactions of ketones and aldehydes with phosphono-acetate esters, (R20)2P(=0)CH2C02R1, produce E/Z mixtures of a, /Tunsaturated esters. Use of the conventional reagent, sodium hydride, gives some selectivity. The combination of tin(II) triflate and A -cthylpipcndine enhances—and sometimes also reverses—the selectivity in most cases studied.71 Six-membered oxo-coordinated tin intermediates are proposed to control the selectivities observed. A similarly selective synthesis of trisubstituted exocyclic alkenes from cyclic ketones has been reported.72... 

Cyclic orthoesters derived from gem-diols offer a further route to alkenes. As part of a three-step conversion, they may be ring opened with hydrobromic acid to give O-acyl bromodeoxy compounds that undergo reductive elimination with copper-zinc. In this way, unsaturated nucleosides have been made by way of mixed 2y3,-bromo-2y3,-deoxy-3,/2, carboxyl-ates.174 A more direct route to alkenes from cyclic orthoesters involves heating in acetic anhydride together with zirconium oxide.175... 

Triethysilyl-protected peroxycarbenium ions (42), generated from acetals (41) on treatment with SnCL, have been developed as the optimal reagents to effect addition to alkenes, which gives rise to a variety of 1,2-dioxolanes (43) in 28-92% yields. This novel method allowed the synthesis of plakinic acid analogues in three steps from the corresponding ketone and alkene.53... 

Alkenes from diols. Reaction of v/c-diols with two secondary hydroxyls or one primary and one secondary alcohol with chlorodiphenylphosphine (2 equiv.), imidazole (4 equiv.), and iodine (2 equiv.) results in alkenes. The reaction presumably involves a vic-iododiphenylphosphinate, which can be isolated in some cases and converted to an alkene with zinc in acetic acid. 

As shown in Table 2, reaction of heteroaromatic compounds with alkynoates occurs under very mild conditions [4, 6]. Heteroaromatic compounds such as pyrroles, furans, and indoles readily hydroarylate alkynoates at room temperature in the presence of a catalytic amount of Pd(OAc)2 in acetic acid or CH2C12, usually affording ds-heteroarylalkenes. This reaction provides a synthetic route to hetero-arylalkenes, especially ds-alkenes, from simple heteroaromatic compounds. 

In an attempt to synthesize (Z)-l,2-dihalo-l-alkenes from bromoboration adducts of 1-alkynes with B-X-9-BBN, all efforts have been unsuccessful. Fortunately, it has found that the haloboration of 1-alkynes with tribromoborane, followed by the reaction with iodine or bromine chloride in the presence of sodium acetate gives the expected (Z)-l,2-dihalo- 1-alkenes stereospecifically (>98%) in good yields (Eq. 122)187>. 

As depicted in the following scheme, a homoallyl alcohol derived from a norbomyl a-diketone underwent a lead(IV) acetate reaction in MeOH, resulting in the formation of a novel methoxy substituted spirocyclic tetrahydrofuran <07CC4239>. It is believed that the addition of the methoxylead(IV) acetate species across the alkene from the less sterically hindered side to form a plumbonium cation leads to the major product after subsequent cyclization and reductive elimination. Moreover, construction of tetrahydrofurans by a Pd(II)/Pd(IV)-catalyzed aminooxygenation of homoallyl alcohols was also reported <07AGE5737>. 

Diphenyl carbonate from dimethyl carbonate and phenol Dibutyl phthalate from butanol and phthalic acid Ethyl acetate from ethanol and butyl acetate Recovery of acetic acid and methanol from methyl acetate by-product of vinyl acetate production Nylon 6,6 prepolymer from adipic acid and hexamethylenediamine MTBE from isobutene and methanol TAME from pentenes and methanol Separation of close boiling 3- and 4-picoline by complexation with organic acids Separation of close-boiling meta and para xylenes by formation of tert-butyl meta-xyxlene Cumene from propylene and benzene General process for the alkylation of aromatics with olefins Production of specific higher and lower alkenes from butenes... 

Palladium metal is too active a catalyst to allow the hydrogenation of an alkyne to stop after one equivalent of H2. To prepare a cis alkene from an alkyne and H2, a less active Pd catalyst is used— Pd adsorbed onto CaC03 with added lead(II) acetate and quinoline. This catalyst is called the Lindlar catalyst after the chemist who first prepared it. Compared to Pd metal, the Lindlar catalyst is deactivated or poisoned. ... 

An alternative approach to the commonly utilized cleavage of allylic isoprenoid compounds (Scheme 16) using attack of +2e in place of H at a Pd° ir-allyl complex also requires a catalyst addition.Electrolysis of allylic acetates with Pb cathode and Pt anode in the presence of Pd(PPh3)4 in MeCN, gave moderate yields of the inner alkenes from both terminal and inner acetates (equations 92 and 93). Control of the regioselectivity was clearly dictated by the attack of H+ from the less-hindered side of the allylic carbanions. 

---