Coupled sequences

The thioboration of terminal alkynes with 9-(alkylthio)-9-borabicyclo[3.3.1]-nonanes (9-RS-9-BBN) proceeds regio- and stereoselectively by catalysis of Pd(Ph,P)4 to produce the 9-[(Z)-2-(alkylthio)-l-alkeny)]-9-BBN derivative 667 in high yields. The protonation of the product 667 with MeOH affords the Markownikov adduct 668 of thiol to 1-alkyne. One-pot synthesis of alkenyl sulfide derivatives 669 via the Pd-catalyzed thioboration-cross-coupling sequence is also possible. Another preparative method for alkenyl sulfides is the Pd-catalyzed cross-coupling of 9-alkyl-9-BBN with l-bromo-l-phe-nylthioethene or 2-bromo-l-phenylthio-l-alkene[534]. 

Hydrometallation is catalyzed by Pd. Hydroboration of l-buten-2-methyl-3-yne (197) with catecholborane (198) gives the 1,4-adduct 199 with 84% selectivity. The ratio of Pd to phosphine (1 1.5) is important[l 10]. The vinyl sulfide 201 is prepared by a one-pot reaction of the thioalkyne 200 via a Pd-catalyzed hydroborution-coupling sequence using dppf as a ligand[l 11]. 

MeOH-H2O/50 °C Scheme 1-28 Diboration orSilylboration-Coupling Sequence... 

The utility of the stepwise, double-coupling procedure is demonstrated in the parallel synthesis of Tamoxifen derivatives on solid support [127] (Scheme 1-29). 1-Alkenylboronates thus obtained by a diboration-cross coupling sequence are further coupled with p-silyUodobenzene supported on polymer resin. Using this strategy, each position about the ethylene core is modified by the appropriate choice of alkyne, aryl halide, and cleavage conditions for the synthesis of a library of Tamoxifen derivatives. 

A tandem palladium-catalysed ort/io-alkylation/intramolecular Heck reaction coupling sequence was used effectively to access in fair yields the tetrahydro 1-benzoxepines 67 from the iodoaryl precursor 66 and the appropriate alkyl bromide. The norbornene plays a relay role in the proposed reaction cycle <06JOC4937>... 

We [43] and, more recently, Maleczka [44] have reported one-pot microwave-assisted hydrostannylations and Stille coupling sequences. Eq. (11.29) depicts one of Maleczka s reactions (see also Eq. 11.32). 

A new pyrrole ring synthesis developed by Arcadi involves the addition of ammonia or benzylamine to 4-pentynones, the latter of which are conveniently prepared via a palladium oxidative coupling sequence as shown below for the synthesis of 40 [39,40]. 

Grigg employed organozinc chemistry to construct 3-alkylidenedihydroindoles such as 91 via a tandem Pd-catalyzed cyclization-cross coupling sequence [112]. A similar route to such compounds was reported by Luo and Wang e.g., 92 to 93 [113]. 

Numerous stannanes have been coupled with halopyridines as electrophiles in the Stille coupling. One of the simplest of these is vinylstannane [82-84]. The Stille reaction of bromopyridine 95 with tributylvinyltin gave angustine (96) [84], an indolopyridine alkaloid. Bromopyridine 95 also took part in a three-component carbonylative-Stille coupling sequence to provide an entry to another indolopyridine alkaloid, naucletine (97) [84]. 

Thermally coupled sequences, for distillation, 22 300-301 Thermally stimulated conductivity (TSC), 19 586... 

An evaluation of numerous clays, including kaolins and bentonites of comparable particle size and distribution, revealed a wide variation in the properties of LDEE-clay composites prepared under identical conditions with similar loadings. This may be attributed to the interference with the radical reactions involved in the coupling sequence. This is confirmed, in part, by the finding that the most effective clays were those which were reported to have been treated with sodium polyphosphate to improve their dispersibility in water during papermaking processes. Solomon reported (1) that treatment of the clays which inhibited radical reactions with sodium polyphosphate reduced the inhibition. 

The first part of the analysis was conducted to detect the designs with minimum energy consumption for the integrated sequences. Once a validated design (tray structure) was obtained, an optimization procedure was carried out on the recycle streams for each of the three coupled sequences to detect the operating conditions under which each design was more energy efficient. 

The application of the SVD technique provides a measure of the controllability properties of a given d mamic system. More than a quantitative measure, SVD should provide a suitable basis for the comparison of the theoretical control properties among the thermally coupled sequences under consideration. To prepare the information needed for such test, each of the product streams of each of the thermally coupled systems was disturbed with a step change in product composition and the corresponding d3mamic responses were obtained. A transfer function matrix relating the product compositions to the intended manipulated variables was then constructed for each case. The transfer function matrix can be subjected to SVD ... 

FIGURE 27. The polar addition mechanism and electron transfer-radical coupling sequence in the addition of lithium pinacolone enolate to benzaldehyde. Reprinted with permission from Reference 28. Copyright 1997 American Chemical Society... 

Alkynones e.g. 51 are efficiently converted into chromones via the enaminoketones in a one-pot reaction offering an attractive route to the heterocycle from salicylic acids by way of a chlorination-Sonogashira coupling sequence which lends itself to combinatorial chemistry (Scheme 30) <99TL2469>. 

Scheme 20 Inter-intramolecular Heck coupling sequences with cyclizations leading to a macrocycle and to 9,10-dihydro-anthracene derivatives. " ...

Scheme 21 Rapid assembly of the mold alkaloid arcyriacyanin A 65 and the skeleton 68 of estrone 69 by inter-intramolecular Heck coupling sequences. ...

The 3-amino-4-phenylpyridine 284, a model unit found in the structure of the antibiotic streptonigrin, has been constructed via a DoM-cross coupling sequence (Scheme 84) [90JCS(P1)2611]. Thus, metalation of the... 

The synthesis of a peptide containing a single p-amino acid residue can be regarded as a simple task involving substituting an a-amino acid by a P-amino acid in the course of a standard peptide coupling sequence. Given the wealth of information available about peptide synthesis, it is inappropriate to consider this option in this section and hence, attention is confined to the incorporation of a p-amino acid into an a-peptide by the use of the Arndt-... 

Conversion of the carboxyl group to a more reactive group and coupling are key steps in peptide synthesis. The coupling reaction must occur readily and quantitatively, and with a minimum of racemization of the chiral centers in the molecule. This last criterion is the Achilles heel of many possible coupling sequences. The importance of nonracemization can best be appreciated by an example. Consider synthesis of a tripeptide from three protected... 

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