HTML table like special layout using bootstrap

HTML

<link rel="stylesheet" href="http://getbootstrap.com/2.3.2/assets/css/bootstrap.css">
<div class="box">
    <div class="row-fluid show-grid">
        <div class="span4">
            <div class="rowspan2">
                <span class="valign-helper"></span>
                a
            </div>
            <div class="rowspan2">
                <span class="valign-helper"></span>
                b
            </div>
        </div>
        <div class="span4">
            <div>c</div>
            <div>d</div>
            <div>e</div>
            <div>f</div>
        </div>
        <div class="span4">
            <div>g</div>
            <div>h</div>
            <div>i</div>
            <div>j</div>
        </div>
    </div>
</div>

CSS

body {
    margin: 50px;
}

.box {
    width: 400px;
    padding: 0 10px;
    background-color: #000;
}

.show-grid [class*="span"] div {
    margin-left: 0;
    margin-top: 10px;
    min-height: 40px;
    line-height: 40px;
    text-align: center;
    margin-bottom: 10px;
    background-color: #fff;
}

.show-grid [class*="span"] .rowspan2 {
    height: 90px;
    margin-bottom: 0;
}

.valign-helper {
    height: 100%;
    display: inline-block;
    vertical-align: middle;
}