199 resultados para Total column moisture


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Total syntheses of (±)-1,4-dimethoxy-6,6-dimethyl-B-norestra-1,3,5(10)-trien-17?-ol(11a), (±)-2,3-dimethoxy-6,6-dimethyl-B-norestra-1,3,5(10)-trien-17?-ol (11b), and (±)-3-methoxy-6,6-dimethyl-B-norestra-1,3,5(10)trien-17?-ol (11c), have been carried out starting from 4,7-dimethoxy-3,3-dimethylindan-1-one (1), 5,6-dimethoxy-3,3-dimethylindan-1-one (2), and 4?-methoxy-3-methylbut-2-enophenone (4), respectively. Generally, it is found that the intermediate 6,6-dimethyl-B-norestra-1,3,5(10),8-tetraen-17?-ols (10), on lithium�liquid ammonia reduction, yield a mixture of 8?,9?- and 8?,9?-trienols, (11) and (12) respectively, in the ratio 1 : 1. This is due to the comparable stabilities of these two isomers. However, the reduction carried out in presence of aniline affords a higher percentage of the 8?,9?-trienol (11). The assignment of configurations is made by chemical and 1H n.m.r. analysis. Catalytic hydrogenation of the tetraenols (10) is shown to proceed via initial isomerisation to the corresponding 6,6-dimethyl-B-norestra-1,3,5(10),9(11)-tetraen-17?-ols (26), followed by hydrogenation from the ?-side to give, exclusively, the 8?,9?-trienols (12).

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The enantiospecific total synthesis of two epimers of the sesquiterpene isocalamusenone has been accomplished starting from the readily available monoterpene (R)-limonene which of the natural product established the stereostructure and the absolute configuration (C) 2010 Elsevier Ltd All rights reserved

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A biomimetic total synthesis of bioactive tetracyclic natural product allomicrophyllone has been achieved in which a protective Diels-Alder reaction employing a disposable sacrificial 1,3-diene directs the regioselectivity of the subsequent Dials-Alder reaction. (C) 2010 Elsevier Ltd. All rights reserved.

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The stability characteristics of a conservatively loaded structure are expected to improve if additional supports are provided to the structure. The same, however, may not be said of a non-conservatively loaded structure; several factors, such as the location and stiffness of supports, type of structure and loading, have a significant influence on the stability characteristics. The influence of an arbitrarily located elastic support on the stability characteristics of a Leipholz column is examined.

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The impact of moisture anomalies on the circulation of the south-west Indian monsoon has been studied with a general circulation model. Newtonian relaxation is adopted to subject the model atmosphere under sustained moisture anomalies. The impact of negative anomalies of moisture was seen as a divergent circulation anomaly, while the positive anomaly was a stronger convergent anomaly. Although the humidity fields display a resilient behaviour, and relax back to normal patterns 1–2 days after the forcing terms in humidity are withdrawn, the circulation anomalies created by the moisture variation keeps growing. A feedback between positive moisture anomalies and low level convergence exists, which is terminated in the absence of external forcings.

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Observational studies indicate that the convective activity of the monsoon systems undergo intraseasonal variations with multi-week time scales. The zone of maximum monsoon convection exhibits substantial transient behavior with successive propagating from the North Indian Ocean to the heated continent. Over South Asia the zone achieves its maximum intensity. These propagations may extend over 3000 km in latitude and perhaps twice the distance in longitude and remain as coherent entities for periods greater than 2-3 weeks. Attempts to explain this phenomena using simple ocean-atmosphere models of the monsoon system had concluded that the interactive ground hydrology so modifies the total heating of the atmosphere that a steady state solution is not possible, thus promoting lateral propagation. That is, the ground hydrology forces the total heating of the atmosphere and the vertical velocity to be slightly out of phase, causing a migration of the convection towards the region of maximum heating. Whereas the lateral scale of the variations produced by the Webster (1983) model were essentially correct, they occurred at twice the frequency of the observed events and were formed near the coastal margin, rather than over the ocean. Webster's (1983) model used to pose the theories was deficient in a number of aspects. Particularly, both the ground moisture content and the thermal inertia of the model were severely underestimated. At the same time, the sea surface temperatures produced by the model between the equator and the model's land-sea boundary were far too cool. Both the atmosphere and the ocean model were modified to include a better hydrological cycle and ocean structure. The convective events produced by the modified model possessed the observed frequency and were generated well south of the coastline. The improved simulation of monsoon variability allowed the hydrological cycle feedback to be generalized. It was found that monsoon variability was constrained to lie within the bounds of a positive gradient of a convective intensity potential (I). The function depends primarily on the surface temperature, the availability of moisture and the stability of the lower atmosphere which varies very slowly on the time scale of months. The oscillations of the monsoon perturb the mean convective intensity potential causing local enhancements of the gradient. These perturbations are caused by the hydrological feedbacks, discussed above, or by the modification of the air-sea fluxes caused by variations of the low level wind during convective events. The final result is the slow northward propagation of convection within an even slower convective regime. The ECMWF analyses show very similar behavior of the convective intensity potential. Although it is considered premature to use the model to conduct simulations of the African monsoon system, the ECMWF analysis indicates similar behavior in the convective intensity potential suggesting, at least, that the same processes control the low frequency structure of the African monsoon. The implications of the hypotheses on numerical weather prediction of monsoon phenomenon are discussed.

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We consider the problem of minimizing the total completion time on a single batch processing machine. The set of jobs to be scheduled can be partitioned into a number of families, where all jobs in the same family have the same processing time. The machine can process at most B jobs simultaneously as a batch, and the processing time of a batch is equal to the processing time of the longest job in the batch. We analyze that properties of an optimal schedule and develop a dynamic programming algorithm of polynomial time complexity when the number of job families is fixed. The research is motivated by the problem of scheduling burn-in ovens in the semiconductor industry

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We study the problem of minimizing total completion time on single and parallel batch processing machines. A batch processing machine is one which can process up to B jobs simultaneously. The processing time of a batch is equal to the largest processing time among all jobs in the batch. This problem is motivated by burn-in operations in the final testing stage of semiconductor manufacturing and is expected to occur in other production environments. We provide an exact solution procedure for the single-machine problem and heuristic algorithms for both single and parallel machine problems. While the exact algorithms have limited applicability due to high computational requirements, extensive experiments show that the heuristics are capable of consistently obtaining near-optimal solutions in very reasonable CPU times.

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Intramolecular alkylation reaction of the bromoenone 12, obtained from S-carvone in three steps, furnished the bicyclo[2.2.2]octenone 13. Contrary to the anticipated radical annulation reaction, the bicyclic bromides 14 and 15, obtained from the enone 13, generated exclusively the cyclopropane product 18 via a 3-exo-trig radical cyclization on reaction with nBu3SnH and AIBN, even in the presence of a large excess of a radicophile. On the other hand, bromoenone 24, synthesized from R-carvone via S-naphthylcarvone 21, underwent radical annulation reaction in the presence of radicophiles to furnish the isotwistanes 25-28 in a regio- and stereospecific manner. Hydrogenation of the olefin 34, obtained from the diketone 27 via a regiospecific Wittig reaction, furnished the naphthyl-5-epipupukean-9-one 33, whereas stereoselective hydrogenation of the enone 36, prepared from the keto ester 25 via a Grignard reaction and dehydration sequence, generated the naphthylpupukeanone 32.

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The details of the first total synthesis of a natural thapsane lg containing three contiguous quaternary carbon atoms, starting from cyclogeraniol (9) '5 described. The Claisen rearrangement of 9 with methoxypropene in the presence of a catalytic amount of propionic acid produced ketone 10. Rhodium acetate-catalyzed intramolecular cyclopropanation of a-diazo-&keto ester 12, obtained from 10 via 8-keto ester 8, furnished cyclopropyl keto ester 7. Lithium in liquid ammonia reductive cleavage of cyclopropyl compound 7 gave a 1:l mixture of hydrindanone 6 and keto1 13. Wittig methylenation of 6 furnished ester 21. Epoxidation of 21, followed by BF3-OEt2-catalyzed rearrangement of epoxide 23 afforded hemiacetal 25. Treatment of hemiacetal 25 with triethylsilane in trifluoroacetic acid furnished lactone 22, a degradation product of various thapsanes. Finally, DIBAH reduction of lactone 22 generated the thapsane

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Acid catalyzed rearrangement of endo 1-methoxytricyclo[6.2.2.0(3,8)]dodec-2-en-10-ol 8c afforded the ketone 9 which has been transformed into (+/-)-norprezizanone 19 thus completing a formal synthesis of (+/-)-zizaene. A key step in this strategy is a stereospecific 1,4-addition of a methyl group

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Schmidt reaction of 5-methoxy or 7-methoxyindan-1-ones or their derivatives results exclusively in isocarbostyrils which are converted into 6-methoxy or 8-methoxyisoquinolines in good yields. This strategy has been extended to the total synthesis of illudinine methyl ester (1b) starting from methyl 8-methoxy-2,2-dimethyl-7-oxo-1,2,3,5,6,7-hexahydro-s-indacene-4-carboxylate (4).

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The formal total synthesis of (+)-didemniserinolipid B, a marine tunicate possessing a 6,8-dioxabicyclo3.2.1]octane framework, was accomplished starting from L-(+)-tartaric acid. The key transformations in the synthesis include the elaboration of a gamma-hydroxy-amide readily obtained by desymmetrization of tartaric acid bis-amide via the controlled addition of a Grignard reagent followed by stereoselective reduction of the resulting ketone. (C) 2010 Elsevier Ltd. All rights reserved.

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The stereoselective synthesis of synargentolide A, a polyhydroxy delta-lactone, has been accomplished from tartaric acid. The key steps in the synthesis involve Keck and Brown allylations and ring closing metathesis. (C) 2010 Elsevier Ltd. All rights reserved.

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A highly stereoselective synthesis of bakkenolide-A (fukinanolide. 1a) employing the radical mediated spirannulation methodology is described.