Recently, new climate change mechanism after 2020 year has been accepted with the parties, and so government is pushing ahead the GHG reduction policies to achieve the effective results. Especially, it is essential to enhance the role of railroad in the public traffic system as well as to develop new cars with high energy efficiency for the GHG reduction of transportation sector. Thus, the calculation method of GHG emission of railroad should be established to manage the emission continuously. In this study, the calculation method of GHG emission of railroad was defined with Tier level considering its emission sources to refer to 2006 IPCC guideline for national GHG inventories. Also, the GHG emission of railroad at Tier 1 level was investigated using the activity data related to the amount of diesel and electricity consumption from 2008 to 2010. As a result, total GHG emission in 2010 was about 2,060 thousands ton CO2e, which have 73% of electricity and 27% of diesel. In future, the plans on the GHG reduction of railroad will be accomplished by the analysis of the detailed trends on the basis of the emission management of Tier 3 level under operating patterns. Therefore, it is important to develop the specific GHG emission factors of railroad in advance.

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Piperidine is one of the most common building blocks of alkaloids.1 For this reason, there have been great efforts to develop new synthetic methods for piperidine structures. Recently, we developed a unique approach to highly substituted piperidin-4-ones, using gold(I)-catalyzed cycloisomerization of mixed N,O-acetals derived from homopropargylic amines.3 In progress of applying this method to total synthesis of natural alkaloids, special attention was given to the bicyclic indolizidine and quinolizidine structures, which are frequently found in various bioactive alkaloids.4 For examples, swainsonine and homopumiliotoxin 223G are well known natural products that contain either indolizidine or quinolizidine core structures. As a consequence, we anticipated that the development of general synthetic routes for the construction of these core structures would assist the total synthesis of natural products bearing azabicyclic systems.As illustrated in Scheme 1, we expected that the indolizidine (n = 1) and quinolizidine (n = 2) bicyclic framework 1 could be easily synthesized from the cyclic enol ether 2, which could be accessed by the gold(I)-catalyzed cycloisomerization of mixed N,O-acetal precursor 3. We intended to prepare the precursor 3 from readily available 4.As depicted in Scheme 2, our initial efforts focused on the preparation of mixed N,O-acetal substrate 8 for the gold(I)-catalyzed cycloisomerization. Epoxidation of PMB ether 5 with m-CPBA followed by the addition of TMS-acetylide and the subsequent desilylation generated homopropargylic alcohol 6 in 36~45% yield over three steps. Transformation of this compound into the homopropargylic amine 7 went uneventfully using a three-step sequence shown in Scheme 2. Preparation of the key substrate 8 was accomplished by the Cbz protection of the amino group followed by the introduc- † This paper is dedicated to Professor Eun Lee on the occasion of his honourable retirement. 2868 Bull. Korean Chem. Soc. 2011, Vol. 32, No. 8 Communications to the Editor tion of MOM group under basic conditions in ~ 90% yield over 2 steps. With mixed N,O-acetal 8 in hand, gold(I)-catalyzed cycloisomerization was successfully carried out to give the vinyl methyl ethers 9 with excellent 86~98% yield.5 Hydration under acidic condition followed by the removal of PMB group generated the alcohol 10 in 64~79% yield (2 steps). The target piperidin-4-ones 11 were prepared using a twostep sequence involving PCC oxidation and the one-pot deprotection-intramolecular imine formation-reduction protocol in 50~69% yield (2 steps). 6,7,8,9 In summary, we studied a new synthetic route to afford indolizidine and quinolizidine core structures by using gold (I)-catalyzed cycloisomerization of mixed N,O-acetals as the key strategy. Total synthesis of structurally complex natural products using this method is currently ongoing in our laboratory.Acknowledgments. We are grateful for the financial support from National Research Foundation of Korea (NRF-331-2008-1-C00165 and NRF-2009-0073749).

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