Network analysis is the examination of activities grouped together by estimated completion times and precedence. Program Evaluation Review Technique (PERT) determines a network's critical path. The critical path, or the longest path through the network, has no "slack" and is the earliest the project can be completed. Included in this stochastic analysis is the critical path's variance. By using the variance and assuming the normal distribution, the analyst can determine the probability for project completion on schedule. Without this confidence level adjustment, there is a 50% probability that the project will be completed on time. Critical Path Method (CPM), which is deterministic, uses the same definition for the critical path and emphasizes time/cost tradeoff. However, the two methods are not completely compatible. Since the 1950s textbook writers and software producers have attempted to combine these methods. The problem occurs when the PERT analysis projects a project out to a specified confidence level and then a project manager places the activities' times into a CPM network. Rather than the cost/time trade-off analysis incorporating calculations that provide a probability of completion at the desired confidence level, the probability of completion is reduced to the original 50%. This may explain why projects are not completed on time. Rather than reconciling the differences, current literature attempts to combine the two and states that there are no differences. This project consisted of the following: conducting a random 100 iteration network simulation, developing a heuristic that allocates expected times for each activity, validating the heuristic by testing 60 networks at 90, 95, and 97.5% confidence levels, and conducting a CPM analysis at 95%. Results using the heuristic revealed a successful allocation of projected activity times at 0.00 percent error. This significant research will assist engineers and managers in making more realistic project completion and cost projections. These findings have a potential for initiating changes in operations research/management science textbooks and in project management software.

Studies directed on the synthesis of the pyrrole containing marine natural products Rigidin and Rigidin E via vinylogous iminium salts are described. The successful strategy relies on the formation of a 2,4-disubstituted pyrrole from a vinamidinium salt followed by acylation at the 5-position of pyrrole. Halogenation and aminocarbonylation at the 3-position of pyrrole followed by hydrolysis of the ester group at C-2 and subsequent Curtius rearrangement generates the pyrrolopyrimidine skeleton. A final deprotection step completes the synthesis of Rigidin and Rigidin E.

A new and efficient relay synthesis of the marine natural products polycitone A and B is described. The new strategy relies on the formation of 2,4-disubstituted pyrroles from a vinamidinium salt followed by electrophilic substitution at the 5-position of the pyrrole and Suzuki coupling at the 4-position to produce the tetrasubstituted heterocycle efficiently and with complete control of regiochemistry.

Numerous novel pyrrole containing marine natural products have been shown to possess interesting biological properties. These compounds have been the synthetic targets of several research groups and we have previously reported synthetic methods which utilize vinylogous iminium salt derivatives as building blocks for analogous pyrrrole systems. We now report a novel and regiocontrolled synthesis of a known pyrrole synthetic precursor to the compounds Lukianol A and Lammelarin O dimethyl ether based on this synthetic methodology.

Reactions of 2,3-disubstituted chloropropeniminium salts and related synthons with ethyl glycinate, ethyl N-methylglycinate, and ethyl N-benzylglycinate have been studied tinder acidic, basic and neutral conditions. Such reactions have resulted in efficient and selective methodology for the synthesis of unsymmetrical 2,3,4-trisubstituted pyrrole systems. (C) 1998 Elsevier Science Ltd. All rights reserved.