Intramolecular reactions, miscellaneous

Amongst miscellaneous intramolecular reactions noted have been intramolecular alkylation of an a,j8-unsaturated ketone at the 7-position [synthesis of ( )-isolongifolene] and an application of intramolecular diyl trapping to the synthesis of linearly fused tricyclopentanoids. The key step in the last example is illustrated from compound (50) it is expected to have utility in syntheses of various natural products. 

Miscellaneous Reactions. Ahyl alcohol can be isomerized to propionaldehyde [123-38-6] in the presence of sohd acid catalyst at 200—300°C. When copper or alumina is used as the catalyst, only propionaldehyde is obtained, because of intramolecular hydrogen transfer. On the other hand, acrolein and hydrogen are produced by a zinc oxide catalyst. In this case, it is considered that propionaldehyde is obtained mainly by intermolecular hydrogen transfer between ahyl alcohol and acrolein (31). 

Silylcuprates have been reported to undergo reactions with a number of miscellaneous Michael acceptors [65]. Conjugate addition to 3-carbomethoxy acyl pyri-dinium salts [65a] affords 4-silyl-l,4-dihydropyridines. Oxidation with p-chlorand generates a 4-acyl pyridinium salt that gives the 4-silylnicotinate upon quenching with water, and methyl 4-silyl-2-substituted dihydronicotinates upon quenching with nucleophiles (nucleophilic addition at the 6-position). The stabilized anion formed by conjugate addition to an a, j8-unsaturated sulfone could be trapped intramolecularly by an alkyl chloride [65b]. 

Lithium butyldimethylzincate, 221 Lithium sec-butyldimethylzincate, 221 Organolithium reagents, 94 Organotitanium reagents, 213 Palladium(II) chloride, 234 Titanium(III) chloride-Diisobutylalu-minum hydride, 303 Tributyltin chloride, 315 Tributyl(trimethylsilyl)tin, 212 3-Trimethylsilyl-l, 2-butadiene, 305 Zinc-copper couple, 348 Intramolecular conjugate additions Alkylaluminum halides, 5 Potassium t-butoxide, 252 Tetrabutylammonium fluoride, 11 Titanium(IV) chloride, 304 Zirconium(IV) propoxide, 352 Miscellaneous reactions 2-(Phenylseleno)acrylonitrile, 244 9-(Phenylseleno)-9-borabicyclo[3.3.1]-nonane, 245 Quina alkaloids, 264 Tributyltin hydride, 316 Conjugate reduction (see Reduction reactions)... 

Section 1.13.5 Miscellaneous reactions. Takeshita and coworkers reported the remarkable use of intramolecular ene reactions to form cycloheptanes and cyclooctanes. Pyrolysis of (216) in toluene at 200 C gives 97% of the cycloheptane (215). Reaction of (216) with SnCU in THF gives 85% of cyclooctane (217), which is an intermediate in the synthesis of cycloaraneosene. 

Miscellaneous Reactions. Intramolecular Wittig reactions of vinyl phos-... 

The following sections will discuss applications of Grignard reagents for metallation. The general categories are intramolecular rearrangements, enolates, and miscellaneous reactions. Eliminations are covered in a separate section. 

Miscellaneous. The phosphonium salt (92) has been shown to be an excellent reagent for the carboalkenylation of carbonyl compounds. For example, the sodium enolate (93) and (92) give a cyclic product (94) which is thought to arise from a stabilized ylide by cyclization via an intramolecular Wittig reaction. 

Miscellaneous coupling reactions. Heck reaction and subsequent intramolecular Michael reaction are probably involved in the aminoarylation of 3-cyclohexenones/ ... 

Miscellaneous ring closure reactions involving carbon-carbon bond formation are shown in Scheme 72 and 73. An oxidation-cyclization-oxidation process was effected by PCC to convert alcohols 197 to 4-piperidones 198 <04JOC3226>. Intramolecular alkylation was used to covert chiral enaminone 199 to 200, a key intermediate in the total synthesis of lepadin alkaloids... 

One of the two reaction types which dominate the synthetic utility of arynes as reactive intermediates is cycloaddition. Cycloadditions can be subdivided into several categories. For example, benzynes undergo [4+2] and [2+2] cycloadditions as well as 1,3-dipolar cycloadditions, the ene reaction, and miscellaneous others. These reactions may occur in an inter- or intramolecular mode. Further, multiple and tandem aryne reactions can be used for multiple-bond construction in a single step. Each of these reaction types, as well as a few miscellaneous reactions, is discussed in the following sections. 

Finally, a few miscellaneous methods for the syntheses of 1,3,2-dioxathiane 2-oxides and 2,2-dioxides have been reported. For example, germacrene-D 199 dropped into an ice-cooled mixture of ether and concentrated sulfuric acid causes the precipitation of sulfate 200 as colorless crystals <1988CPB3161>. The formation of the intramolecular cyclic sulfate was proven by IR and H and NMR spectroscopy (Scheme 57). The treatment of 2,5-norborna-diene with Phl/oleum provided a mixture of cyclic sulfates in 72% yield with the six-membered stmcture 202 being preferred (Scheme 57) <1986ZOR450>. Finally, a few 1,3,2-benzodioxathiins 204 were synthesized from the enaminones 203 by reaction with oleum or chlorosulfuric acid <1991AP949>. 

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