Phase- vanishing halolactonization of neat substrates

• Nicole Windmon and
• Veljko Dragojlovic

Beilstein J. Org. Chem. 2008, 4, No. 29, doi:10.3762/bjoc.4.29

• -dibromopentanoate (4) (Scheme 2). Apparently, 4,5-dibromopentanoic acid underwent hydrogen bromide-catalyzed transesterification with ethyl acetate. In a control experiment, 4-pentenoic acid was transesterified by dissolving it in ethyl acetate and adding a catalytic amount of HBr in acetic acid. The best results

Stereoselective synthesis of (2S,3S,4Z)-4-fluoro- 1,3-dihydroxy- 2-(octadecanoylamino)octadec- 4-ene, [(Z)-4-fluoroceramide], and its phase behavior at the air/water interface

• Gergana S. Nikolova and
• Günter Haufe

Beilstein J. Org. Chem. 2008, 4, No. 12, doi:10.3762/bjoc.4.12

• provided the desired tert-butyl imino acid ester 5 as a mixture with the ethyl imino acid ester 6 (formed due to a partial transesterification of 4 with the titanium reagent) and four non-identified compounds (among them most likely diastereomers of the title compounds) in a ratio of 57:28:7:1:2:5

Unexpected degradation of the bisphosphonate P-C-P bridge under mild conditions

• Petri A. Turhanen and
• Jouko J. Vepsäläinen

Beilstein J. Org. Chem. 2008, 4, No. 7, doi:10.1186/1860-5397-4-7

• several times, but the result was always the same (formation of 1a was observed in all experiments), though in some experiments a transesterification of the acetyl group to C(O)OEt group was observed in yields of 0–13% as confirmed by the 1H and 31P NMR spectra. We were unable to provide any direct

• explanation for the variation in the transesterification proportion. Etidronic acid was also tested as a starting material to prepare a derivative such as 1a [C(O)OEt group instead of Ac group], but the reaction did not occur under the same conditions as those used in the preparation of 1a. Our subsequent

• ) partial transesterification of bisphosphonate 1a before degradation of P-C-P bridge, 2) partial esterification of phosphonate group after the carbonate groups (R3) decomposition from compound 1a (this is proposed to occur rapidly after the addition of 40% NaOH) and before the degradation of P-C-P bridge

Large- scale ruthenium- and enzyme- catalyzed dynamic kinetic resolution of (rac)-1-phenylethanol

• Krisztián Bogár,
• Belén Martín-Matute and
• Jan-E. Bäckvall

Beilstein J. Org. Chem. 2007, 3, No. 50, doi:10.1186/1860-5397-3-50

• -phenylethanol (2) is addressed. The immobilized lipase Candida antarctica lipase B (CALB) was employed for the resolution, which shows high enantioselectivity in the transesterification. The ruthenium catalyst used, (η 5-C5Ph5)RuCl(CO)2 1, was shown to possess very high reactivity in the "in situ" redox

• , Candida antarctica lipase B, catalyzes the transesterification with excellent selectivity in the presence of the homogeneous ruthenium racemization catalyst 1. Isopropenyl acetate seems to be an appropriate acyl donor, which makes the purification of the product acetate very easy via simple distillation

Investigation of acetyl migrations in furanosides

• O. P. Chevallier and
• M. E. Migaud

Beilstein J. Org. Chem. 2006, 2, No. 14, doi:10.1186/1860-5397-2-14

• and Table 4). The proportion of intermolecular transesterification and de-esterification products increased when anhydrous KF conditions were used instead of commercial TBAF in THF (Table 3, condition C). Similarly, longer reaction time of the fluoride-catalysed desilylation reactions resulted in an

• acetyl moieties. Such direct transesterification is intermolecular and while it has been observed in nucleoside-phosphoramidite and glycoside chemistry,[20][21][22][23] this alkoxide-promoted intermolecular acetyl migration process has been overlooked in furanosides. The isolated quantities of 1c and 1d

• decreased by a factor of two upon dilution (1:10) when 1 was reacted with TBAF, while 1b formation remained rapid with no detection of 1a formation. Similarly, complete transesterification took place when riboside 6 was treated with acetyl riboside 1 under basic conditions (Scheme 6). Acetyl migration in