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New insights into the AKD sizing mechanism Kyle J. Bottorff and Mark J. Sullivan, Hercules Incorporated, Wilmington, Delaware, USA Keywords: Alkylketene dimers, AKD, Reaction mechanisms, Solid State "C NMR, Sizing, P-Keto acid, P-Keto calcium salt, P-Keto ester, AKD oligomers. SUMMARY: Paper samples sized with 13C labeled alkylketene dimer (AKD) dispersions were characterized by solid state carbon NMR resulting in direct evidence supporting the forma- tion of AKD-cellulose P-keto esters on AKD sized paper. A series of AKD reaction products that may

synthesized in turn, from the P-keto ester 6. For the synthesis of 6 we started with enone 1, readily prepared following a known procedure.6 The analysis of the IH NMR spectrum of the reaction product of its reduction revealed the presence of a 2: 1 mixture of allylic alcohols and also that the acetal moiety had been hydrolyzed, presumably during the work-up, giving directly 8. Scheme 1 @ C02Me - 4 5 683 0 I JJ pc"o C02Me 6 684 J. A. BACIGALUPPO eta/. We have found no precedent in the literature for the hydrolysis of acetals under these conditions. Without

sterically congested enamides 14. 3. P-Hydroxy Esters Enantiomerically pure P-hydroxy esters have served extensively as valuable chiral building blocks in synthetic organic and natural product chemistry.17 One of the most direct routes to enantiomerically-enriched P-hydroxy esters is through asymmetric hydrogenation of the corresponding P-keto esters, and several highly enantioselective catalyst systems have been developed for this transformation. For example, Ru-BINAP catalysts have been shown to provide a wide range of P- hydroxy esters with very high selectivity

2 SYNTHESIS OF KEY INTERMEDIATE (4 ) FROM THE SEVEN-MEMBERED p-KETO ESTER ( 5 ) 2.1 Model test of the formation of hydroazulene by pinacol coupling A Michael addition of compound (10) to acrolein gave keto- aldehyde (ll), which was subjected to pinacol coupling to afford the diol (12). Diol (12) was oxidized to the hydroxy-ketone (13) with DMSO and trifluoroacetic anhydride. However, oxidation of (12) with PPC gave (13) in very poor yield, the major product being the open-ring compound (11). Compound (13) proved to be a mixture of trans and cis isomers

16 (67%) as the monohydrate. Reaction of 16 with the phenethylamine derivative 17 afforded the keto-imine 18 (61%). This reaction appeared to take place by initial formation of a Schiff base at the central carbonyl, followed by a Pictet- Spengler cyclization and rapid oxidative decarboxylation of the resulting p-keto-ester. Methylation (SO%), and subsequent hydride reduction (72%) led directly to the cordrastines (diastereomeric ratio of 1 2 in favor of 20). Scheme 4 @Cl &olBu P O I B U ' PPh, Me0 C02Et Me0 ' CO,Et PPh3 Me0 2 equiv. Me0 1 4 1 5 Me0

agents constitute a versatile entrke to fbnctionalized amino acid derivatives. The synthesis of W-azirine-2-carboxylic esters fiom aziridine-2-carboxylic esters by an eliminative reaction is reported. An alternative preparation of 2H-azirine-2-carboxylic esters involves an alkaloid mediated synthesis from the oxime tosylates of p-keto esters by a modified Neber reaction. Aziridine-2-carboxylic esters are of interest in view of their structural relationship with a- as well as p-amino acids and the intrinsic high reactivity of the three-membered ring. Little

segments, we made a decision to embark on the development of a general strategy for the synthesis of these molecules.To initiate the synthesis of batzelladine A (lo), we first investigated a synthetic protocol for the 0 1998 IUPAC, Pure and Applied Chemistry70,303-306 Anti-HIV compounds 305 NH NH 10 11 left hand bicyclic guanidine segment (11) starting from ethylacetoacetate (scheme 5). It was first converted into the a-alkylidene-p-keto ester derivative (12) and then subjected to conjugate addition with concomitant cyclisation using 0-methylisourea to give 13

followed by immediate protection of the unstable alcohol gave ethoxyethyl ether 12 (Scheme 3). Diazo transfer reaction of the p-keto ester 12 under standard conditions furnished diazo compound 13, which was subjected to copper-mediated cyclopropanation to give the bicyclic ketone 14. Reduction of ketone 14 with sodium borohydride, acetylation of the resultant alcohol, hydrolysis of the ethoxyethyl ether, and subsequent ozonolysis of the olefin furnished the aldehyde 11. Scheme 3.a 12 13 0 OAc C d EE 14 11 a (a) NaH, THF, 0 "C, then BuLi; sorbic aldehyde, 0 to

-t-BuOH mixture is excellent for p-keto ester reductions. **NB-Enantrane gives 86%. Therefore *. Fig. 25. Optimum reagents for asymmetric reduction of representative ketones. It is noteworthy that with two exceptions, Bind-H and Terashima's reagent, all of the most favorable reagents are boron derivatives. ALLYL- AND CROTYLBORATION Simple organoboranes, such as triethylborane do not add to the carbonyl group. However, as was first pointed out by Mikhailov, allylboron derivatives undergo a fast addition, which proceeds with allylic rearrangement (Fig. 26, ref. 29). R

enzymatic hy- drolysis. Model experiments by using methyl P-keto- esters showed that P-ketoester linkages were stable un- der the conditions for the cellulase treatments. The enzy- matically-hydrolyzed residues were subjected to IR and GC analyses. Table I shows results of the cellulase treatments. The yield of the sheet 1 (7.0%) after the treatment was higher than for the sheet 2 (3.5%), because the residue of the sheet 1 contained fillers. AKD contents in the residues of the sheets 1 and 2 were 0.92 and 0.23%, respectively, when these values were determined