Можно сделать с помощью
grid так:
<div class="box">
<div class="box__box">1</div>
<div class="box__box">2</div>
<div class="box__box">3</div>
<div class="box__box">4</div>
<div class="box__box">5</div>
<div class="box__box">6</div>
</div>
.box {
background-color: brown;
display: grid;
gap: 5px;
padding: 20px;
}
.box__box {
height: 100px;
min-height: 100%;
box-sizing: border-box;
border: solid;
background-color: white;
}
.box__box:nth-child(1) {
grid-column: 1;
grid-row: 1;
grid-row-start: 1;
grid-row-end: 3;
}
.box__box:nth-child(6) {
grid-column: 2;
grid-row: 3;
grid-row-start: 3;
grid-row-end: 5;
}