Phosphoranes condensation with

A basically different approach to sialic acid synthesis was recently described by Mirzayanova et al. (1970) (Figure 13). N-Acetyl-o-manno-samine was subjected to the cyanohydrin reaction, the cyano group converted to an aldehyde, and the latter condensed with phosphorane XLVII via the Wittig reaction. Mild hydrolysis gave a crystalline product that was identical to natural NANA in elemental analysis, optical rotation, melting point, chromatographic behavior, and color reactions. 

In a similar way the use of the 2-methyl-3-isothiocyanato-4-thiocyanato-hept-3-ene (252) prepared from thiocyanogen and the oxoal-kylene phosphorane (251) yields the 2-anilino-4-propyl-5-isopropyl-thiazole (253) by condensation with aniline (Scheme 128). 

Trimethylstannyl)ethylidene]phosphoranes have been generated by conjugate addition of trimethylstannyllithium to triphenylvinylphosphonium bromide30 and, more efficiently, by deprotonation of the corresponding / -(trimethylstannyl)phosphonium salt31, and condensed with aldehydes and ketones. 

The 1,3,2-dioxaphosphorinans (101 R = Cl, NMe2, or OMe), derived from trans-2-hydroxymethylcyclopentanol, condensed with perfluorobiacetyl to give the expected phosphoranes.64 That from (101 R = OMe) probably had the relationship of methoxy to ring junction shown in (102) it slowly isomerized in solution at 40 °C to a 60 40 mixture with the isomer (103). The corresponding isomerizations... 

Formate esters behave as typical carbonyl compounds in reactions with a number of ylides, eliminating phosphine oxide and forming vinyl ethers, e.g. (33).35 Stabilized phosphoranes are able to condense with the carbonyl group of cyclic thioanhydrides (34).38 Quinoline derivatives, e.g. (35), are obtained from the condensation of dicar-boalkoxy-ylides with isocyanates.37 Benzoyl isothiocyanates and keto-phosphoranes give quantitative yields of (36), which are unreactive in Wittig reactions but can be readily oxidized by selenous acid.38 The products obtained from reactions (Scheme 9) with the triazolinedione (37) depend upon the stability of the ylide used.39... 

After these results had established the feasibility of generating and utilizing a carbohydrate phosphorane, the two systems that had been reported earlier were examined in order to determine if similar conditions would allow them to undergo the Wittig reaction. The ylide derived from phosphonium salt I condensed with both benz-aldehyde and U-chlorobenzaldehyde to produce good yields of olefinic products Villa and Vlllb. The ylide derived from phosphonium salt II also was successfully condensed with benzaldehyde, but the yield of IX was only 30 , presumably because of its extremely poor solubility even in an HMPA-THF solvent mixture. Both of these systems supported the tenet that it was possible to use unstabilized carbohydrate phosphoranes if the conditions are proper and if the g-oxygen is attached to the carbohydrate through another set of bonds. 

The highly unstable trimethylsilylformaldehyde is prepared by Swern oxidation at very low temperature. An in situ condensation with a stabilized phosphorane delivers a silylolefin. If the solution of trimethylsilylformaldehyde is allowed to reach 0°C, no condensation product is obtained, which proves that trimethylsilylformaldehyde is not stable in... 

These in situ oxidations, followed by condensation with a phosphorous reagent, are normally not possible on ketones, because of their lack of reactivity with stabilized phosphoranes and phosphonate anions. Nevertheless, one-pot condensation with ketones can occur in very favourable... 

The 1,3-ditelluretane 88 is obtained as a minor product along with the 1,3-ditellurafulvene 89 by the reaction of phenylacetylide with tellurium followed by acidification with trifluoroacetic acid (Scheme 27) <2003TL2397>. In the reaction of trimethylsilylethynyl tellurolate, use of tifluoroacetic acid in /-butyl alcohol at — 20°C leads to the formation of the 1,3-ditelluretane 90, presumably via the telluraketene 91. Vilsmeier-Haack reaction on the crude ditelluretane 90 furnishes dialdehydes 27 and 92 in 10% yield. 1,3-Ditelluretanes 27 and 92 can be transformed into other derivatives, as shown in Scheme 28. An /. // mixture of 27 and 92 condenses smoothly with phosphorane to give diester product 93. The reaction with diesterdithiole phosphonate or dithiole phosphonate affords 1,3-ditelluretane derivative 94 or 95, respectively. 

The ( )-double bond at C-6 of a racemic JH1 is formed by condensation of ethyl ketone 178 with phosphorane 194 in the New Brunswick synthesis. In this synthesis about 40 % (Z)- and 60 % ( )-isomer were formed which were separated by preparative gas chromatography. Compound 182 was converted into ( )-JHl by use of the phosphonate method 148,149) (Scheme 36). Applying two Wittig reactions and a phosphonate condensation the same authors could prepare racemic JH2 171148,149) (Scheme 36). 

Citranaxanthene 543 is found in citrus fruits and is used as a food dye like P-carotene. The same phosphonium salt synthon 505 as used for the vitamin A synthesis is monoolefinated with the polyene dialdehyde 539. The Wittig reaction of the resulting 540 with phosphorane 541 followed by aldol condensation of the obtained 542 with acetone gives citranaxanthene 54 3 255,263) (Scheme 92). In the preparation of the polyenedial 539 l,4-dibromo-2-butene 544 is reacted with trimethyl... 

Charge a single-necked round-bottomed flask (100 mL) with phosphorane 9 (1.1 g, 1.65 mmol), a magnetic stirrer bar, o-xylene (20 mL), and a catalytic amount of hydroquinone. Furnish with a reflux condenser closed by a mercury valve or a septum/balloon combination and flush the entire set-up with nitrogen. Stir and heat the mixture to 145°C for 10 h. 

Z)-condenses with aldehydes in a (Z)-stereoselective Wittig reaction to afford diethyl acetals of (Z)-a,jS-unsaturated aldehydes in 57-86% yield. Hydrolysis of the acetals with p-TsOH as catalyst in acetone-water or with moist silica gel (2 days at 23°) affords the corresponding (Z)-unsaturated aldehydes in 47-98% yield. The product usually contains 4-14% of the (E)-isomer. These results contrast with those of Wittig reactions of formylmethylenetriphenylphosphorane and l,3-dioxolan-2-ylmethylenetriphenyl-phosphorane (5, 269), which afford (E)-unsaturated aldehydes. 

The dialdehyde 150 was condensed with malononitrile to give the donor-acceptor compound 151 <20020L2581>. Condensation with different phosphoranes and phosphonates gave the dendralene-type vinylogs of tetrathiafulvalene 50-52 and the donor-acceptor compound 152 <20020L2581>. 

Pyrones are obtained as side products (or possibly intermediates) by condensation with one mole of acylmethylene-phosphorane. ... 

The synthetic route to 619 is a rather lengthy 27-step sequence outlined in Scheme 87 [192]. The first key reaction is a Wittig olefination of 606 with phosphorane 620 to give 621 with > 98% Z-selectivity. Subsequent Claisen rearrangement of the free alcohol 622 provides 623 with >98% stereoselectivity. Dieckmann condensation followed by decarboxylation gives the thermodynamically more stable ran -cyclopentanone 624 trans cis ratio = 7 1). 

Vilsmeier reaction to the chloroaldehyde (106), followed by reductive meth-ylation, yielded the aldehyde 107 (Scheme 14) with the precedented stereochemical outcome. Attempted halogenation of the derived neopentyl-type alcohol was unsuccessful under a variety of conditions, so an alternative scheme involving two successive Wittig-type reactions was developed. The aldehyde 107 was converted to the unsaturated aldehyde 108 by the method of Nagata and Hayase. Reduction with triethylsilane and tris (triphenylphosphine) rhodium chloride was followed by condensation with isopropylidene phosphorane to give the desired product 109. 

Reaction (7.283) can be used to obtain a tetra azaphosphorane which will condense with its fluoro derivative to give a bis phosphorane with a P-P bond [10]. 

Reactions with Aldehydes. The sulfonyl-stabilized phosphorane reagent has been used for Wittig alkenation of aldehydes. For example, condensation with isonicotinaldehyde gave the a,p-unsaturated sulfone as a single fisomer in 76% yield (eq 3). It is noteworthy that analogous reaction with (methylsulfonylmethy-lene)triphenylphosphorane produced the corresponding methyl-sulfonyl alkene as a 1 1 mixture of the E/Zisomers. ... 

The sulfone-alkylation method of Julia (1968) was a significant advance in retinoid total synthesis and has potential utility for labeled s)mthesis work. But the most useful reactions that have been adapted for the preparation of labeled retinoids are the well-developed procedures for the Wittig (Pommer, 1960) and the Homer-Emmons reactions (Bautagy and Thomas, 1974). These reactions are for synthesis of unsaturated and trans- and cw-a,p-enone compounds from the condensation of aldehydes and ketones with phosphoranes and with phos-phonoacetates, phosphonoacetonitrile, and oxophosphonates. These reactions suggest profitable application to the synthesis of retinoids, including labeled materials. 

Condensation of o-acyloxybenzyl bromides with phosphoranes gives chromenes (Scheme 51) and a simple variation gives isochromenes. Application of the procedure to acyclic dibromo-compounds yields dihydrofurans or dihydropyrans. ... 

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