Lifelong Machine Learning for Topic Modeling and Classification

Machine Learning (ML) has been successfully used as a prevalent approach for many computational tasks and applications. However, most ML algorithms are designed to address a specific problem using a single dataset. That is, given a dataset, an ML algorithm is run on the dataset to build a model. Although this one-shot learning is very important and useful, it can never make an AI system intelligent, and its accuracy is also limited. Lifelong Machine Learning (LML), on the other hand, aims to design and develop computational systems and algorithms that learn as humans do, i.e., retaining the results learned in the past, abstracting knowledge from them, and using the knowledge to help future learning and problem solving. The rationale is that when faced with a new situation, we humans use our previous experience and knowledge to help deal with and learn from the new situation. It is essential to incorporate such a capability into a computational system to make it more versatile, holistic, and intelligent. This thesis presents my Ph.D. research work on designing lifelong machine learning approaches for both unsupervised learning and supervised learning. For unsupervised learning, we focus on the area of topic modeling, which aims to discover coherent semantic topics from the documents. For supervised learning, we propose to improve the problem of classification with the integration of lifelong machine learning. Topic modeling has been widely used to uncover topics from document collections. Such topics are important in many text mining and machine learning tasks such as classification, retrieval, clustering and summarization. However, classic unsupervised topic models can generate many incoherent topics. To address them, we proposed several knowledge-based topic models (Chen et al., 2013d; Chen et al., 2013b; Chen et al., 2013c) which require the knowledge to be provided by domain experts. To further ameliorate the topic quality from topic models, in (Chen and Liu, 2014b; Chen and Liu, 2014a), we proposed to automatically extract, accumulate and filter knowledge with the idea of LML, i.e., lifelong machine learning. The experimental results shown in these papers demonstrate the effectiveness of the proposed LML approaches. We also apply LML for supervised learning, specifically classification. Classification is a widely studied machine learning task. The goal is to classify certain objects into a fixed set of categories. Deviated from traditional classification problem which focuses on a single domain, we proposed our Lifelong Sentiment Classification (LSC) model (Chen et al., 2015) which automatically extracts and accumulates sentiment oriented knowledge. Such knowledge is utilized using regularization under the Naive Bayesian optimization framework. The experimental results demonstrate that our proposed LSC model is able to accomplish better and better classification performance with knowledge accumulated from an increasing number of domains, which shows the advantages of having LML. Based on this thesis, we believe that the Lifelong Machine Learning (LML) capability can lead to more robust computational systems to overcome the dynamics and complexity of real-world problems to produce better predictability

DDQ-Mediated Oxidative Radical Cycloisomerization of 1,5-Diynols: Regioselective Synthesis of Benzo[<i>b</i>]fluorenones under Metal-Free Conditions

A regio- and chemoselective oxidative cycloisomerization reaction of acyclic 1,5-diynols has been developed. The reaction proceeds under metal-free reaction conditions with high efficiency and broad functional group tolerance, which offers a general and straightforward access to benzo­[<i>b</i>]­fluorenones under metal-free conditions. The preliminary mechanistic studies revealed the possible involvement of a Meyer–Schuster rearrangement combined with an oxidative radical cyclization

Transition-Metal-Catalyzed Hydrosulfoximination and Oxidation Reaction for the Synthesis of Sulfoximine Derivatives

We report herein a Au/Ag-cocatalyzed chemoselective hydrosulfoximination reaction of simple ynamides with free <i>N</i>H-sulfoximines, which produces the <i>N</i>-alkenylated sulfoximidoyl derivatives with quantitative atom efficiency and good to excellent yields. Further elaborations of the enamine isomers under Ru-catalyzed oxidative conditions to cleave the CC double bonds can selectively afford urea-type sulfoximines. The aforementioned catalytic reactions provide new opportunities for the convergent and straightforward access to sulfoximine derivatives

Silver Triflate and Palladium Acetate Co-catalyzed Reaction of <i>N</i>′-(2-Alkynylbenzylidene)hydrazide with <i>N</i>-Allyl Ynamide

A silver triflate and palladium acetate co-catalyzed reaction of <i>N</i>′-(2-alkynylbenzylidene)hydrazide with <i>N</i>-allyl ynamide is described, which generates 2-amino-<i>H</i>-pyrazolo[5,1-<i>a</i>]isoquinolines in good to excellent yield. The transformation proceeds with high efficiency through 6-<i>endo</i> cyclization, [3 + 2] cycloaddition, 3,3-sigmatropic rearrangement, and aromatization

Silver Triflate and Palladium Acetate Co-catalyzed Reaction of <i>N</i>′-(2-Alkynylbenzylidene)hydrazide with <i>N</i>-Allyl Ynamide

A silver triflate and palladium acetate co-catalyzed reaction of <i>N</i>′-(2-alkynylbenzylidene)hydrazide with <i>N</i>-allyl ynamide is described, which generates 2-amino-<i>H</i>-pyrazolo[5,1-<i>a</i>]isoquinolines in good to excellent yield. The transformation proceeds with high efficiency through 6-<i>endo</i> cyclization, [3 + 2] cycloaddition, 3,3-sigmatropic rearrangement, and aromatization

Silver Triflate and Palladium Acetate Co-catalyzed Reaction of <i>N</i>′-(2-Alkynylbenzylidene)hydrazide with <i>N</i>-Allyl Ynamide

A silver triflate and palladium acetate co-catalyzed reaction of <i>N</i>′-(2-alkynylbenzylidene)hydrazide with <i>N</i>-allyl ynamide is described, which generates 2-amino-<i>H</i>-pyrazolo[5,1-<i>a</i>]isoquinolines in good to excellent yield. The transformation proceeds with high efficiency through 6-<i>endo</i> cyclization, [3 + 2] cycloaddition, 3,3-sigmatropic rearrangement, and aromatization

Platinum-Catalyzed Tandem Cycloisomerization Reaction of Benzoendiynyl Esters: Regioselective Long-Range 1,5-Acyl Migration

A Pt^II-catalyzed intramolecular chemo- and regioselective pentannulation/long-range 1,5-acyl migration reaction is described. This cascade cycloisomerization protocol produces a wide variety of benzofulvene diketones in good to excellent yields with exclusively the <i>Z</i> configuration of the exocyclic double bond of the final product. The ¹⁸O isotope experiment together with ¹³C NMR, HRMS, and HMBC analyses confirmed an interesting long-range acyl rearrangement process in this transformation

Novel Silver Tetrafluoroborate Catalyzed Electrophilic Cascade Cyclization Reaction: A Facile Approach to the Synthesis of Halo-Substituted Benzo[<i>a</i>]fluorenols

A facile and novel silver tetrafluoroborate catalyzed electrophilic cascade cyclization reaction to generate halo-substituted benzo[<i>a</i>]fluorenols under mild conditions is disclosed. Good chemical selectivity and mild reaction conditions were involved in the transformation. The halide-containing benzo[<i>a</i>]fluorenols could be further elaborated via palladium-catalyzed cross-coupling reactions to introduce complexity

Copper-Catalyzed Diversity-Oriented Synthesis (DOS) of 4‑Amino‑2<i>H</i>‑chromen-2-imines: Application of Kemp Elimination toward O‑Heterocycles

We report herein a copper-catalyzed sequential multicomponent reaction of benzo­[<i>d</i>]­isoxazoles with terminal alkynes and sulfonyl azides, which produced divergent 4-amino-2<i>H</i>-chromen-2-imines with excellent chemical selectivity. The reaction tolerated a broad range of functional groups, and released only N₂ as the sole byproduct. The sulfonyl imino group could be removed to give biologically active free 4-amino-2<i>H</i>-chromenone in good yield

α‑Palladation of Imines as Entry to Dehydrogenative Heck Reaction: Aerobic Oxidative Cyclization of <i>N</i>‑Allylimines to Pyrroles

We report here a palladium(II)-catalyzed oxidative cyclization reaction of <i>N</i>-allylimines derived from methyl ketones, typically acetophenones, affording pyrrole derivatives at room temperature under oxygen atmosphere. The reaction likely proceeds through α-palladation of the imine followed by olefin migratory insertion and β-hydride elimination, thus representing a new example of aerobic dehydrogenative Heck cyclization